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Inherited Differences in Weight and Conformation of Bronze Turkeys
Inherited Differences in Weight and Conformation of Bronze Turkeys V. S. ASMUNDSON Division of Poultry Husbandry, University of California, Davis (Received for publication March 29, 1948)
characters such QUANTITATIVE as body weight, width of breast,
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tween them. Weights and measurements for these two strains and strain 2, which length of shank and length of keel vary was intermediate between them, have considerably within strains and varieties. been given elsewhere (Asmundson 1944) Various strains of Bronze turkeys also dif- for the year 1941. Strain 3 was crossed fer significantly from each other in these with strain 2 and inherited differences in characters (Asmundson 1944). The dif- width of breast were found (Asmundson ferences between varieties and strains are 1945). Strain 3 is a medium sized Broad inherited (Knox and Marsden 1944, As- Breasted Bronze, while strain 1 is a relamundson 1945) and at least in the case of tively small, narrow breasted, inbred breast width there is some variation which strain of Bronze, which is descended from is independent of weight of bird, although Bronze turkeys used by producers in Calihere, as in the case of length of keel and fornia about twenty years ago. Birds of shank, there is correlation with weight strain 1 have not been particularly se(Asmundson 1944). For length of shank lected for size or conformation and have Jaap (1938) has estimated that 25.3 per- not been crossed with Broad Breasted cent of the male and 39.0 percent of fe- Bronze at any time, hence, carry no genes male variance is caused by heredity. from that strain or variety. Some data are The present series of experimental mat- also given for Broad Breasted Bronze ings was started to obtain data on the strains 4 and 5 and the progeny from mode of inheritance of weight and confor- crosses of these and other strains. mation by using strains of Bronze turkeys The birds were hatched at two week inthat differ widely in weight and width of tervals from the latter part of March breast. The data were also analyzed sta- through the early part of May. Each year tistically to obtain estimates of the influ- the poults from three to five hatches were ence of differences between the sexes on used. They were floor-brooded with elecweight and the measurements used and trically heated hovers. At eight weeks of of weight on the latter. The paper by age they were moved to dirt yards. El-Ibiary and Jull (1948) points to the imFeed and water were before the birds all portance of such studies in order than an the time. An attempt was made to feed explanation may be found for the appar- rations that should give equivalent reent differences between the various pub- sults in successive years. Owing to war lished reports. conditions this attempt was not entirely successful since lower weights were atMATERIALS AND METHODS tained on the average in. 1944 and 1945 Most of the data presented in this paper than in 1943 and 1946 (Table 1). The birds were weighed and measured are for strains 1 and 3 and crosses be-
TABLE 1.—Means at 24 weeks of age
Birds in group No.
Group
Weight of bird, kilos.
Length of shank, cm.
Length of keel, cm.
Width of breast at point above lower surface of keel shown,, cm. 1 cm.
2 cm.
3 cm.
17 9 9 32
Females- -1943 4.54 15.35 16.14 5.56 15.97 6.01 16.03 5.93
14.72 15.67 15.47 15.12
2.96 3.50 3.68 4.23
4.18 5.04 5.32 5.86
5.22 6.37 6.74 7.25
Strain 1 F, (Str. 3 9 9 X S t r . l d V ) Fi(Str. 1 9 9 X S t r . $
17 20 23 44
Males— -1943 18.98 6.74 19.96 8.82 19.60 8.78 19.77 8.10
17.04 18.62 18.52 17.56
2.94 3.27 3.38 3.78
3.99 4.69 4.79 5.42
4.94 5.97 6.11 6.86
11 19 13 9 14 . 27 47
Females--1944 3.83 14.67 15.49 4.42 15.80 5.06 15.53 4.87 15.32 4.61 15.87 5.16 16.02 4.94
14.28 14.58 15.09 14.80 14.39 14.58 14.16
2.88 3.15 3.37 3.43 3.49 3.96 3.95
4.01 4.41 5.00 4.94 4.91 5.63 5.54
5.05 5.51 6.22 6.08 6.04 6.86 6.74
Strain 1 Fi 9 9 XStr. lcTc? Fi(Str. 3 9 9 XStr. left?) Fi(Str. 1 9 9 XStr. S
7 17 3 10 15 15 21
Males—-1944 6.01 18.67 18.99 6.56 18.40 6.09 19.74 7.21 18.75 6.42 19.40 7.07 20.06 7.33
16.19 16.34 15.97 16.63 16.01 17.14 16.19
2.71 3.11 3.13 3.25 3.10 3.52 3.65
3.83 4.36 4.47 4.61 4.53 5.07 5.21
4.73 5.51 5.53 5.83 5.62 6.38 6.50
Strain 1 Fi (Str. 3 9 9 XStr. l d V ) Fi(Str. 1 9 9 XStr. 3
15 7 23 60 42 56
Females--1945 15.03 4.17 15.76 5.23 15.87 5.12 15.72 4.86 16.28 5.15 15.97 5.08
14.47 15.17 15.02 14.82 14.81 14.22
3.14 3.74 3.46 3.62 3.69 3.88
4.51 5.34 5.00 5.18 5.24 5.56
5.67 6.70 6.37 6.55 6.70 6.96
Strain 1 Fi(Str. 3 9 9 XStr. lefc?) F, (Str. 1 9 9 XStr. Z
12 8 14 43 42 45
Males—-1945 18.81 6.28 19.64 8.14 19.03 7.40 19.43 7.04 20.02 7.54 19.51 7.27
16.67 17.55 17.14 16.83 17.03 16.21
2.93 3.58 3.30 3.31 3.56 3.68
4.10 5.06 4.61 4.72 5.09 5.26
5.12 6.43 5.84 5.97 6.45 6.63
Strain 1 Fi 9 9 XStr. Fi (Str. 3 9 9 Fi(Str. 1 9 9 F2 F, 9 9 XStr. Strain 3
36 17 28 8 82 12 28
Females--1946 15.54 4.30 15.91 4.85 16.25 5.39 16.04 5.37 15.97 5.06 16.13 5.47 16.26 5.56
14.25 14.84 15.10 15.15 14.82 14.80 14.58
3.13 3.24 3.47 3.46 3.49 3.60 3.83
4.59 4.86 5.24 5.34 5.30 5.38 5.74
5.94 6.32 6.78 6.83 6.77 6.88 7.38
22 10 17 8 49 18 25
Males-—1946 18.86 5.99 19.79 7.56 20.51 8.86 20.05 8.29 19.79 7.27 20.22 8.10 20.14 8.04
16.20 17.25 17.64 17.91 16.65 16.89 16.77
2.90 3.14 3.46 3.36 3.32 3.50 3.61
4.14 4.48 5.20 4.84 4.86 5.16 5.30
5.27 5.71 6.78 6.12 6.27 6.63 6.76
Strain 1 Fi 9 9 X S t r . Fi (Str. 3 9 9 F,(Str. 1 9 9 F2 Fi 9 9 XStr. Strain 3
Strain 1 Fi 9 9 XStr. F, (Str. 3 9 9 Fj (Str. 1 9 9 F2 Fi 9 9 XStr. Strain 3
lrf>c? XStr. I t i V ) XStr. 3
lcTc? XStr. lcfc?) XStr. 3d 1 d") 3d"d 1
1
lcfd XStr. lcfc?) XStr. 3
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Strain 1 Fi (Str. 3 9 9 X S t r . lcfc?) Fi (Str. 1 9 9 XStr. 3o'er 1 ) Strain 3
GENETICS OF WEIGHT AND CONFORMATION IN TURKEYS
at 24 weeks as described before (Asmundson 1944). RESULTS OF CROSSING STRAINS 1 AND 3
breast increase after the birds are 24 weeks old. In general, the length of shank varied with body weight but there were minor exceptions; such minor exceptions also occurred in the data for crosses between Bronze strains 2 and 3 (Asmundson 1945). The Fi progeny tended to have shorter shanks that the birds of strain 3. Out of the 16 Fi groups, four had longer shanks than the strain 3 birds. Three of these four (see males 1943, 1945, 1946) were larger than corresponding strain 3 birds, while the one group of females in 1943, which were smaller than the corresponding strain 3 birds, did not have significantly longer shanks, since the difference was 0.11 +0.15 and therefore less than its standard error. The F2 progeny and those obtained by backcrossing on strain 1 males had shanks that were in most cases shorter than those of all others except strain 1. These facts again suggest that autosomal genes determine length of shank, that longer is dominant to shorter shank length and that while general size factors largely determine the length of shank, other genes may also have an effect. It may be pointed out in this connection that the "short" gene in turkeys, an autosomal recessive, also reduced body weight (Asmundson 1944a). Other evidence presented below also shows that special size factors probably play a very minor role in determining length of shank. Length of the keel of the sternum. The keels of the birds of strain 1 were not consistently shorter or longer than those of strain 3. The Fi progeny had, with the exception of the one small group of males in 1944, consistently longer keels than the parental strains. The progeny of back crosses on the parental strains also had consistently longer keels on the average than the parental strains. The F 2 progeny,
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The averages at 24 weeks are presented in Table 1. The birds of strain 1 were consistency smaller than those of strain 3, and differed from the latter in all measurements, except length of keel. The analyses of variance of the data (Table 2) shows that there were in each case statistically significant differences. Weight of bird. The Fi progeny frequently equalled or exceeded the average weight of the larger (strain 3) parent. The Fi from reciprocal matings did not differ consistently, hence weight is here determined by autosomal genes. If weight at 24 wee.ks were determined by sexlinked genes, the female progeny of strain 1 females X strain 3 males should outweigh those from the reciprocal cross, while this was only so in one of the four years. The progeny of the backcross on strain 3 males weighed slightly more than the birds of strain 3 except in the case of the females in 1946. None of the differences were statistically significant. On the other hand the progeny of the backcross on strain 1 males were (with one doubtful exception of 3 Fi males in 1944) intermediate in weight between the Fi and strain 1. The F 2 progeny also weighed less than the Fx progeny. These data show, beyond reasonable doubt, that large size, as measured by weight, is dominant to small size in this cross. Length of shank. The smaller birds of strain 1 had uniformly shorter shanks (tarsometatarsi) on the average than those of strain 3. Since the tarsometatarsal bones stop growing at about 20 weeks (Kodinetz, 1940; Asmundson and Lerner, 1942) the length of shank is about the same as that of the mature bird, while body weight, length of keel, and width of
697
698
V. S. ASMUNDSON TABLE 2.—Mean squares—for 24 week old birds. All values of F are significant (see footnotes)
Source of variance
Degrees of freedom No.
Body weight, kilos
Length of shank, cm.
Width of breast at point above lower surface of keel shown, cm.
Length of keel, cm.
1 cm.
2 cm.
3 cm.
66 3 63
Females—1943 .65 0.39 7.91 5.32 .30 0.15 26. 34.42
0.47 2.06 0.40 5.15
0.93 6.18 0.68 9.07
0.74 10.56 0.27 38.55
1.05 15.46 0.37 42.33
Total Between means of groups Within groups
103 3 100
Males—1943 1.33 0.55 17.44 3.40 .85 0.46 20.58 7.34
1.11 12.29 0.77 15.90
0.21 3.31 0.12 28.03
0.49 9.03 0.23 39.34
1.03 15.83 0.59 26.95
Total Between means of groups Within groups F2
139 6 133
0.68 1.19 0.62 3.08
0.47 3.30 0.34 9.71
0.62 6.61 0.35 18.89
0.76 8.05 0.44 18.30
Total Betwen means of groups Within groups F2
87 6 81
0.75 2.15 0.64 3.35
0.19 1.16 0.12 9.77 .
0.39 2.58 0.23 11.28
0.61 4.18 0.35 11.92
Total Between means of groups Within groups F3
202 5 197
Total Between means of groups Within groups F3
163 5 158
Total Between means of groups Within groups
210 6 204
148 6 142
Females—1944 .57 0.49 3.16 3.39 .45 0.36 7.05 9.42 Males—1944 1.67 0.96 1.06 4.27 .10 0.71 10.42 5.99 Females—1945 .33 0.35 2.69 3.92 .27 0.26 9.95 15.08
1 2 3 4
Significant Significant Significant Significant
values of F:P=.05, values of F : P = . 05, values of F : P = . 05, values of F:P=.05,
0.18 1.56 0.15 10.40
0.39 3.02 0.32 9.44
0.36 4.40 0.26 16.92
0.75 4.76 0.63 7.56
0.14 1.48 0.10 14.80
0.27 3.53 0.17 20.76
0.44 5.89 0.26 22.65
Females—1946 .38 0.25 5.68 1.92 .23 0.20 24.89 9.60
0.43 2.51 0.37 6.78
0.10 1.47 0.06 24.50
0.29 4.03 0.19 21.21
0.39 6.17 0.22 28.05
Males—1946 1.50 0.66 17.20 5.65 .84 0.45 20.47 12.56
1.03 5.43 0.84 6.46
0.11 1.22 0.06 20.33
0.28 3.58 0.14 25.57
0.47 6.28 0.23 27.30
.74 4.68 .61 7.65
p-4
Total Between means of groups Within groups F4
0.49 3.73 0.41 9.10
9 9 9 9
9 9 9 9
Males—1945 0.66 4.06 0.56 7.25
-2.75, -2.17, -2.26, -2.14,
9 9 9 9
9 9 9 9
-4.11, -2.94, -3.11, -2.89,
cfc? d'c? cfc? cTc?
-3.98. -3.04. -3.14. -2.93.
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Total Between means of groups Within groups
GENETICS OF WEIGHT AND CONFORMATION IN TURKEYS
These results are in good agreement with those obtained before (Asmundson 1945) when crosses were made between strains 3 and 2, the latter an improved strain selected for good conformation but without any admixture of Broad Breasted Bronze in its ancestry. RESULTS WITH OTHER BROAD BREASTED BRONZE The question might well be asked as to whether the results obtained when strain 3 is crossed with strain 1 are typical of those which would be obtained if other broad breasted strains were used. Data obtained in 1946 are available on this point for two additional strains (Table 3). Of the two, strain 4 are straight Broad Breasted Bronze, while strain 5 are of mixed origin, but the birds conform approximately to the broad breast standard by having a width of about 3§ inches at If inches above the keel. There were statistically significant differences between the various groups (see Table 5 below), particularly strain 4 and 5. The male birds in strain 4 weighed about the same as those in strain 3 while the females of strain 4 were slightly heavier. Strain 5 birds were smaller, had shorter shanks and a shorter keel than the birds in strains 3 and 4. The birds of strains 3 and 5 did not differ significantly in width of breast, while both had narrower breasts than those in strain 4. Thus, for the females of strains 3 and 4 the difference in width of breast at 1 cm. above the keel of 0.30 cm. is statistically highly significant (t = 3.00, p = <01). The data in Table 3 show that when males from strain 4 were crossed with hens of strains 1 and 5, the progeny were wider breasted than the progeny obtained from strain 3 males mated to strain 1 and 5 females. The progeny from strain 5 females X strain 3 or 4 males were wider
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however, did not consistently have longer or shorter keels than the parental strains. With one exception (males 1944) the F 2 progeny had shorter keels than the corresponding Fi progeny. These differences cannot be attributed to differences in weight, since, for example, the Fx progeny did not in all cases weigh on the average more than the birds of the parental strains. The data for length of keel suggest that the parental strains had different dominant genes for length of keel and that these act like complementary genes in such a way as to produce longer keels in the Fi progeny (AaBb>AAbb or aaBB). The recombinations obtained in the F2 again produced shorter keels but not quite so short as those of the parental strains. These results suggest the dominance of genes for long keel over those for short keels. There is no indication of sexlinked genes but in view of the absence of consistent differences between the parental strains, the evidence on this point is not conclusive. Width of breast. The two strains differed significantly in width of breast with the birds of strain 3 having wider breasts that those of strain 1. The Fi progeny were in all cases intermediate between the parental strains and there were no consistent differences between the Fi progeny from reciprocal crosses, hence the differences in breast width are determined by autosomal genes. There is no indication of dominance. While width of breast obviously varies to some extent with weight of bird, there is considerable independent variation, otherwise width of breast would follow differences in weight more closely. It is also apparent that more than one pair of genes is involved, since the backcross progeny were intermediate between the ¥1 progeny and the parents.
699
700
V. S. ASMUNDSON
TABLE 3.-—Averages for 24-week-old Bronze turkeys in 1946. Comparisons of strains 3 and 4 Weight,
Description of group
No.
Strain 4 Strain 5 Hens* X Strain 3 cfc?1 Hens* X Strain 4c?
23 41 22 24 18 40 28
Females 5.68 4.83 5.42 5.67 5.52 5.77 5.67
Strain 4 Strain S Hens* X Strain 3 d V Hens* X Strain 4c? cf HenstXStrain3cTcr HenstXStrah^cTc? Str. 3 9 9 X Str. 4c? d"
21 32 23 13 19 37 21
8.07 6.65 7.91 8.31 8.32 7.97 8.62
Length of shank, cm.
Length of keel, cm.
Width of breast 1 cm. above keel, cm.
16.33 15.88 16.22 16.23 16.09 16.28 16.50
14.86 13.77 14.84 15.08 14.72 14.65 14.73
4.13 3.76 3.65 3.85 3.72 4.02 3,97
20.08 19.36 20.16 20.20 20.21 20.10 20.42
16.86 15.45 16.81 17.15 17.22 16.88 16.73
3.91 3.58 3.46 3.67 . 3.55 3.66 3.88
Males
breasted than those from strain 1 females mated to strain 3 or 4 males (details not shown in Table 3, but compare line 5 under females and under males in Table 3 with line 4 under "females-1946" and "males-1946" in Table 1). The width of breast of the progeny thus varies according to the width of breast of the parents as one might expect, since there is no dominance of wide over narrow breast (see above). The data further show that strain 4 males, when crossed with other strains, not only produced wider breasted progeny than strain 3 males, but also larger progeny at 24 weeks. These results indicate that the width of breast of the progeny of any two different strains of turkeys may be expected to vary according to the width of breast of the parental strains. On the other hand, weight of bird cannot be accurately predicted from the weights of the strains crossed, which agrees with results reported before when different varieties were crossed (Asmundson 1942) although in most cases the progeny approached or exceeded the weight of the larger parents
at 24 weeks of age. However, when Knox and Marsden (1944) crossed a small variety (Beltsville Small White) with large Broad Breasted Bronze, the progeny were intermediate. GENETIC VARIATION WITHIN THE BROAD BREASTED BRONZE
The data for strains 3 and 4 were further analyzed as shown in Table 4. The data for all male and female progeny were first separately totaled and averaged. From the averages a correction factor was calculated. The data for each male were then recalculated as follows: weight divided by 1.47; length of shank divided by 1.24; length of keel divided by 1.14; width of breast at 1 cm. above the keel multiplied by 1.05. The number of progeny from each of the 21 dams varied from 2 to 14 and there were two or three dams (mates) to each of the eight sires. The differences between the means of full sib families (dams) were statistically highly significant, while those between sires were not.
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* Hens out of strains 1 and 3—Fis or backcrosses on strain 3. f Hens of strains 1 and strain 5.
GENETICS OF WEIGHT AND CONFORMATION IN TURKEYS
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TABLE 4.—Mean squares/or 24-week-old Broad Breasted Bronze turkeys in 1947. Combined data, with those for males corrected to those for females
Source of variation
Degrees of freedom
Weight
Length of shank
142 7 135 13 122
0.509 1.539 0.456 1.581 0.336 0.972 4.720
0.260 0.957 0.224 0.896 0.153 1.068 ,5.874
Total Between sires Within sires Between dams Between full sibs F* value for sires F* value for dams
Length of keel 0.540 2.014 0.463 2.170 0.282 0.928 7.710
Width of breast at 1 cm. above the keel 0.105 0.531 0.083 0.393 0.050 1.351 7.892
' The 5 % value of F is, for sires 2.85, for dams 1.81; the 1% value of F is, for sires 4.46, for dams 2.36 portant since they point to the need for constant selection to maintain whatever standards are adopted. Moreover, the data show the importance of careful selection of dams as well as sires. Such a conclusion of course, also comes from the finding that the characters dealt with are determined by autosomal genes. RELATION OF CONFORMATION TO SEX A very high percentage of the total
TABLE 5.—Mean squares. Upper part (A) based on data for 24-week-old males and females in 1946 {Table 1); lower part (B) based on 1946 data used in Table 3, plus those in the same year for Strain 3 {means in Table 1) Source of variation
Degrees of freedom
Total Between sexes Within sexes Between groups Within groups F (between sexes) F (between groups)
359 1 358 12 346
Total Between sexes Within sexes Between groups Within groups F (between sexes) F (between groups)
414 1 413 15 398
Percentage of total' variation accounted for by differences between Sexes A Sexes B Groups A Groups B
Length of keel
Width of breast 1 cm. above keel
4.08 1,312.73 0.42 3.78 0.30 347.28 12.60
1.76 389.98 0.68 3.97 0.57 98.23 6.96
0.11 1.23 0.10 1.35 0.06 0.91 22.50
4.07 1,516.77 0.41 102.87 0.35 14.74 293.91
1.93 424.80 0.90 34.65 0.69 12.26 50.21
0.14 4.73 0.13 0.88 0.11 5.38 8.00
89.71 89.93 2.94 1.47
61.36 53.37 6.25 10.88
9.09 7.14 36.36 14.29
Weight
Length of shank
Part A 2.38 552.72 0.85 11.36 0.48 48.65 23.67 PartB 2.38 589.08 0.96 45.44 0.76 12.96 59.79
64.29 59.66 15.55 8.40
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The highly significant differences between dams (Table 4) show that there is genetic heterogeneity within Broad Breasted Bronze supposedly free from admixture with other varieties. The fact that the differences are between full sib (sister-brother) families has no special significance. A larger sampling with males selected at random undoubtedly would reveal statistically significant differences between sire families. The results are im-
702
. V. S. ASMTJNDSON
recommended by Bird (1945). Apparently the fact that the measurements would thereby be taken at a greater distance above the keel in males than in females did not eliminate the difference between the sexes observed when the measurements are made at a fixed point above the keel (see Tables 1 and 3). Sex differences have also been observed in the growth of bones and muscles of younger birds (Asmundson and Lerner 1940). RELATION OF MEASUREMENTS TO WEIGHT
Length of shank, length of keel and width of breast at 1 and 5 centimeters above the keel are known to be positively correlated with weight of bird (Asmundson 1944). As a first step to determine relationships for the birds in strains 1 and 3 and their crosses, the zero order correlations were calculated for the largest series available, the 24 week-old females in 1946, and the males in that same year (Table 6). All of the coefficients of correlation based on the total variation and the variation within groups were statistically significant except between length of shank and width of breast for within groups. Most of the coefficients between means of groups for females and for males were not significant. It has been pointed out above that males are larger—that is, weigh more, have ionger shanks and longer keels— than females of the same age and similar ancestry. The males also have deeper bodies, Asmundson (1944), Bird (1945). From this it would be expected that combined uncorrected data for males and females might give a negative correlation for length of shank, length of keel and even weight with width of breast. The sex differences would make any conclusion drawn from correlation coefficients based on the total variation in such data for
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variation (Table 5) in weight, length of shank, and length of keel, or about 60, 90 and 60 percent respectively is accounted for by differences in sex. The figures for length of shank are in good agreement with the 91 percent reported by Jaap (1938a). Sex differences account for less than 10 percent of the variation in breast width, while differences between groups account for a higher percentage but less than variation within groups. The percentage of the total variation accounted for by differences between groups and within groups is in each case less for weight and length of keel than for width of breast, while it is least for length of shank. The differences between the sexes were, with the exception of width of breast (in Part A of Table 5), highly significant. These, differences in weight, length of shank, and length of keel of 24-week-old males and females have long been recognized, while little attention has been paid to the difference in width of breast. Nevertheless, an examination of tables 1 and 3 shows that the difference in width of breast is as consistently expressed as the other differences—the males being narrower than the females. Since the difference between sexes in width of breast was not statistically significant for one of the two groups in Table 5, it seemed advisable to further analyze the data in Table 1. For each group the average difference was calculated for width of breast at 1 cm. above the keel by subtracting the width of breast of the males form that of the corresponding group of females. The average difference thus obtained between the 24 pairs of groups was .2025, which, using the method of Fisher (1932) proved to be statistically highly significant (t = 8.33, p = <.01). This agrees with El-Ibiary and Jull (1948) who measured width of breast at a point above the keel one fifth of the depth as
703
GENETICS OF WEIGHT AND CONFORMATION IN TURKEYS TABLE 6.—Coefficients
of correlation and regression 24-week-old males and females, 1946 Weight and
Degrees Length of shank of freedom Regression
Length of shank and Width of breast a t 1 cm. above the keel
Length of keel Regression
Length of keel
sion
Width of breast at 1 cm. above keel
Length of keel a n d width of breast at 1 cm. above keel Regression
Regression
Regres- sion
Total Between groups Within groups
210 6 204
.650 .981 .424
.47 .57 .40
. 703 .680* .754
.75 .45 .96
.633 .906 .431
Females .33 I .440 .46 .709 .23 | .378
.58 .91 .51
.345 .863 .127
.43 .75 .33
.238 .366 .204
.12 .28 .08
Total Between groups Within groups
.48 6 142
.793 .982 .674
.53 .56 .49
.785 .832 .805
.65 .47 .81
.644 .827 .485
Males .17 ) .606 .22 .743 .13 I .564
.76 .73 .77
.468 .906 .174
.19 .42 .06
.352 .462 .319
.11 .22 .08
Total Between sexes Between groups Within groups
359 1 12 346
.900 1.000 .985 .585
.909 .998 .802 .780
Males and females .852 1.000 .732 .491
.211 .997 .820 .435
038 -.997 .409 .255
.050 .997 .085 .550
males and females useless, hence the last part of Table 7 was not calculated until after the paper by El-Ibiary and Jull (1948) appeared. The correlation between means of sexes has no significance since n - 2 = 0 (Fisher 1932). It will be observed, however, that the correlation between means of sexes for width of breast with weight, length of shank and length of keel is in each case negative while the other coefficients are positive. All of the coefficients for between groups and within groups are positive and all of the latter are statistically significant.
Sampling might account for some of the differences in the coefficients of correlation based on total variation, in Table 6, from those reported by El-Ibiary and Jull (1948). Accordingly correlations were calculated (Table 7) for three groups of Broad Breasted Bronze in 1946. One of these three groups comprised strain 3 which was also included in the data, used to calculate Table 6. Since there were three groups, only the coefficients based on the total variation are shown in Table 7 for the females and for the males but for the combined data the same coeffi-
TABLE 7.—Coefficients of correlation based on body weiglits and measurements of 24-week-old Broad Breasted Bronze only ' Source of variation
Degrees of freedom
Weight and Weight and Weight and W * Length of Length of shank and shank and keel and length of length of width of length of width of width of shank keel breast* keel breast breast
Total
78
.571
Females .805
.430
.599
.090
.338
Total
66
.723
Males .733
.447
.543
.168
.155
145 1 4 140
.980 1.000 .923 .659
Males and females .915 -.016 1.000 -1.000 -.158 .462 .783 .426
.861 1.000 -.069 .581
-.219 -1.000 .304 .116
-.679 -.999 .719 .235
Total Between sexes Between groups Within groups
' Italics indicate significant values at p = .(ji.
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Italics indicate significant values at £ = . 0 1 (Fisher, 1932).
704
V . S. ASMUNDSON TABLE 8.—Coefficients of partial correlation with variation in body weight eliminated. Based on data in Table 6 Measurements correlated
Total
Shank and keel Shank and width Keel and width
-.030 -.112 -.376
Shank and keel Shank and width Keel and width
-.044 -.092 -.324
Between means of groups Females .279 -.314 -.806 Males -.706 .884 -.725
Within groups
.098 -.068 -.204 -.049 -.238 -.138
significant and between groups, where it is positive. For both males and females, the coefficient based on the total variation for length of keel with width of breast is negative and statistically significant. These results are consistent with those previously obtained (Asmundson 1944) in showing that, when variation in weight is eliminated, there is no consistent statistically significant relation between the length of shank and the length of keel nor between the length of shank and width of breast, while length of keel and width of breast are negatively correlated. Moreover, they lend no support to the conclusion of El-Ibiary and Jull (1948) that for good breast conformation birds should be selected for relatively short shank and long keel. For the 24-week-old males and females in 1946 (Table 1) the regression of the three measurements (length of shank, length of keel, and width of breast) on weight was calculated (Table 6). The regression coefficients based on variation within groups were then used to calculate corrected measurements for each of the 211 females and 149 males by using the difference in weight between the individual and the mean weight of the entire population of females and of males respectively. The analyses of the data so obtained are in Table 9. These data show that when the shank length was corrected
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cients are presented as in Table 6. Here the coefficients between means of sexes again are negative for width correlated with weight, length of shank or length of keel. These same coefficients based on total variation are also negative but only the last (length of keel correlated with width of breast) is statistically significant. Again the coefficients based on variation within groups are all positive, although two (width with length of shank and with length of keel are not statistically significant. The data in these tables show fairly conclusively that the correlation between weight, length of shank, length of keel, and width within sexes is positive. These coefficients of correlation are usually statistically significantly except between length of shank and width of breast and in some cases (Table 7) length of keel and width of breast. The negative correlation between length of shank and width of breast obtained by Ibiary and Jull apparently stems basically from lumping together the data for the larger, narrower breasted males with those for the females. A further statistical analysis of the data was made in order to obtain evidence about (1) the extent to which length of shank, length of keel, and width of breast are correlated independent of weight and (2) to find out whether significant differences would remain between groups after these measurements were corrected for differences in the weight of the birds. From the values of r in Table 6, the coefficients of partial correlation were calculated, with the effects of differences in weight eliminated (Table 8). The coefficients of partial correlation for length of shank with length of keel were not significant. This was also true for length of shank with width of breast except in the case of the males for within groups, where the coefficient is negative and statistically
GENETICS OF WEIGHT AND CONFOKMATION IN TURKEYS TABLE 9.—Analyses of variance for 24-week-old females and males in 1946, based on measurements corrected for regression on weight
210
Between means of groups Within groups F
6 204
Total
148
Between means of groups Within groups F
142
Females 0.17 0.26 0.24 0.16 1.50
Width of breast 1 cm. above keel 0.06
3.03 0.18 16:83 Males 0.30 0.48
0.53 0.05 10.60
0.34 0.29 1.1
0.51 0.04 12.75
8.37 0.15 55.61
0.64
for regression on weight, there was no longer a statistically significant difference in the length of shank of the various groups. The implication is clear that the differences in the length of shank of the two strains (1 and 3) and the progeny obtained by crossing them are due primarily to differences in weight. On the other hand significant differences in length of keel and width of breast remain after thus correcting for differences in weight. These results indicate that it would be difficult to select for change in length of shank without changing weight of bird, or vice versa. This indeed was what Lerner (1943) found with White Leghorn chickens. Length of keel and width of breast should respond to selection and corresponding changes in weight should not necessarily follow. DISCUSSION
The data in this paper on inheritance of body weight and width of breast are in good agreement with earlier results for Bronze (Asmundson 1945) in that large size as measured by body weight at 24 weeks of age is dominant to small size, while there is no dominance of wide over
narrow breast, the Fi progeny being intermediate. When other varieties were crossed (Asmundson 1942) the results for the most part agreed with those for crosses between different strains of Bronze, the Fi progeny weighing about as much as the larger parent, or more than either parent. Knox and Marsden (1944) reported different results for a cross between Bronze and Beltsville Small White, the Fi progeny being intermediate and closer to the smaller parent, thus indicating dominance of genes for small size. They also reported that the length of shank of the Fi progeny was intermediate and closer to the small parent which would be expected in view of the fact that length of shank appears to be determined largely by general size factors. The results reported in this paper indicate that for both shank and keel, long is dominant to short. Our results indicate that weight and conformation are determined by autosomal genes. In general, our results for inheritance of body weight and length of shank appear to agree well with the conclusion of Knox and Marsden that they are typical of quantitative characters. The results in this paper for length of keel and width of breast cannot be compared with these of Knox and Marsden for breast type. Regardless of differences in dominance, the evidence available indicates that weight and conformation are inherited and therefore subject to change by selection. The question still remains as to the relation between weight and depth of body, length of shank (tarsometatarsus) or other long bones of the extremities, length of keel and width of breast. In general the heavier birds have longer shanks, but the bones are shorter per unit of weight in larger than in smaller birds, as pointed out by Asmundson and Lerner 1942. (Bird (1945) has reported an exception—the larger Broad Breasted
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Total
Length of keel, cm -
70S
706
V. S. ASMTJNDSON
the coefficients been calculated separately for each sex, it is to be expected that such results would not have been obtained. Our results (Tables 6 and 7) clearly indicate that when data for males and females are combined, the sample used will also determine the size of the coefficient and whether it is positive or negative. The facts stated above; namely, that males are larger and have narrower breasts than females clearly imply that when the uncorrected data for males and females are combined, some (but not all) samples of populations may be expected to show significant negative correlation between width of breast and any measure of size such as weight, depth of body, length of shank and length of keel. The implications of the various relationships mentioned above indicate that when birds are selected for breeding purposes, length of shank may be ignored or considered, with body weight as a measure of size. For example, selection for shorter shank and heavier body weight would cancel each other and is therefore impractical. On the other hand, there is apparently sufficient variation in length of keel and in width of breast independent of variation in weight to permit of changing the relationships between these through selection. Normally, however, an increase in width of breast or in length of keel will result in an increase in body weight; also selection for a wider breast without an increase in weight will normally result in a shorter keeled bird and vice versa. Some selection for moderate length of keel would therefore seem advisable when birds are selected for width of breast but the statement of El-Ibiary and Jull (1948) that selecting birds for long keels would result in birds otherwise "excelling in roundness of breast" does not appear to be justified by the available facts. Rather the facts suggest that the
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Bronze had shorter tibias than the Standard Bronze males). This is well illustrated by the data in Tables 1 and 3. The females have shorter shanks than the males but a simple calculation will show that per unit of body weight the males have shorter shanks than the females. It is obvious that the average differences in length of shank of the males or of the females considered separately are less than the differences in their weights. This indicates that the term, relatively short shank, which is based on the length of the shank in terms of weight, is meaningless. Thus the Broad Breasted Bronze birds of strain 3 have a longer shank than the narrower breasted birds of strain 3 (Table 1) but, being heavier, the former may be said to have relatively shorter shanks. No harm would be done by the use of this phrase if it were not inferred that there was some causal relation between width of breast and relative length of shank. Such a relationship has been inferred from weights and measurements by Jaap (1938) and Bird (1945). When these inferences are subjected to statistical analysis, it is found that the various measurements are positively correlated with weight and with each other. However, when the effect of weight is eliminated by use of the coefficient of partial correlation, it is found that length of shank is not usually correlated with length of keel nor with width of breast. On the other hand there is a low but significant negative correlation between length of shank and width of breast. These results and the conclusions drawn from them are diametrically opposed to those of El-Ibiary and Jull (1948). The negative correlation obtained by them for length of shank and width of breast is apparently primarily due to basing the calculation of the coefficient of correlation on the combined, uncorrected measurements for both males and females. Had
GENETICS OF WEIGHT AND CONFORMATION IN TURKEYS
selection should be simply for width or roundness of breast, if greater width or roundness is the objective. Whether such selection would result in any change in the length of the bones should perhaps be considered an open question in view of the data published by Bird, but all other evidence argues against such a result. SUMMARY
tween the parental strains in width of breast; there was no difference in the width of breast of the progeny from reciprocal matings. The progeny from backcrosses were in each case intermediate between the Fis and the parental strain. Width of breast is thus determined by nondominant autosomal genes. The progeny of strain 4 and strain 3 males, both broad breasted, were compared. Strain 4 birds had wider breasts than those in strain 3. The breast width of the progeny varied with the width of breast of the parents, while body weights did not. Significant differences in weight, length of shank, length of keel, and width of breast were found between full sib families of Broad Breasted Bronze. Significant sex differences were observed with the males being larger (as measured by body weight, length of shank, length of keel) and narrower breasted. The percentage of the total variation accounted for by differences in sex accounted for nearly 90 percent for length of shank, about 60 percent for weight and for length of keel, and less than 10 percent for width of breast. The coefficients of correlation for two partly overlapping populations of 24week-old males and females in 1946 were calculated. The length of the bones and width of breast were positively correlated with weight. When the influence of weight was eliminated there was no correlation (based on the coefficient of partial correlation) between length of shank and length of keel, nor was there any consistent correlation between length of shank and width of breast, while length of keel and width of breast were negatively correlated. When the measurements were corrected for weight by using the regression coefficient for within groups, the difference between means of groups was insignificant
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Two strains of Bronze (Nos. 1 and 3) which differed in weight and width of breast were crossed. Fis, F2S, and the progeny of backcrosses to the males of the parental strains were raised. All birds were weighed and measured (length of left shank, length of keel, width of breast) at 24 weeks of age. The Fi progeny equalled or exceeded the larger Broad Breasted Bronze parent and there was no difference in the progeny from reciprocal matings. The F2 progeny weighed less than the Fis; the progeny .from the backcross on the larger parent equalled the parental weight, while those from the other backcross were intermediate between the Fis and the smaller parental strain. These results show that heavy (large) is dominant to light and that weight here is determined by autosomal genes. The results for length of shank were, in general, similar to those for weight although some apparent differences occurred. The two strains did not differ consistently in length of keel, while the Fi and backcross progeny had, with one doubtful exception, longer keels than the parental strains. The F2s had shorter keels than the Fis but they did not have consistently longer keels than the parental strains. These results suggest that the parental strains had different dominant complementary genes. The Fi progeny were intermediate be-
707
708
V. S. ASMUNDSON
for length of shank but remained statistically highly significant for length of keel and for width of breast. I t is concluded from these results that selection for change in length of shank would result in a change in weight, whereas such would not necessarily be the case when length of keel or width of breast are changed by selection. REFERENCES
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Asmundson, V. S., 1942. Crossbreeding and heterosis in turkeys. Poultry Sci. 21: 311-316. Asmundson, V. S., 1944. Measuring strain differences in the conformation of turkeys. Poultry Sci. 23:21-29. Asmundson, V. S., 1944a. Inherited shortening of the long bones in the turkey. Jour. Heredity 35: 295-299. Asmundson, V. S., 1945. Inheritance of breast width in turkeys. Poultry Sci. 24: 150-154. Asmundson, V. S., and I. M. Lerner, 1940. Growth of turkeys. I. Influence of strain, sex, and ration. Poultry Sci. 19:49-54. Asmundson, V. S., and I. M. Lerner, 1942. Growth
of turkeys. II. Relative growth of the Tarsometatarsus. Poultry Sci. 21: 505-510. Bird, S., 1945. Determination of fleshing characteristics in market poultry. II. Turkeys. Scientific Agric. 24: 481-488. El-Ibiary, H. M., and M. A. Jull. 1948. Criteria and genetic variation of live body conformation in turkeys. Poultry Sci. 27: 40-52. Fisher, R. A., 1932. Statistical methods for research workers. 4th edit. Oliver and Boyd, Edinburgh. Jaap, R. G., 1938. Estimating the influence of heredity on the tarso-metatarsal length of the domestic turkey. Proc. Oklahoma Acad. Sci. 19: Jaap, R. G., 1938a. Body conformation of the live market turkey. Poultry Sci. 17: 120-125. Knox, C. W., and S. J. Marsden, 1944. The inheritance of some quantitative characteristics in turkeys. Jour. Hered. 35: 89-97. Kodinetz, G., 1940. Beitrag zur Kenntnis der Rasse und der Entwicklung des Zagioraner Truthuhnes (Meleagris gallopavo). Zeitschr. f. Tierzucht. u. Zucht.-biol. 47:140-165. Lerner, I. M., 1943. The failure of selection to modify shank growth ratios of the domestic fowl. Genetics 28: 80-81.
characters such QUANTITATIVE as body weight, width of breast,
695
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tween them. Weights and measurements for these two strains and strain 2, which length of shank and length of keel vary was intermediate between them, have considerably within strains and varieties. been given elsewhere (Asmundson 1944) Various strains of Bronze turkeys also dif- for the year 1941. Strain 3 was crossed fer significantly from each other in these with strain 2 and inherited differences in characters (Asmundson 1944). The dif- width of breast were found (Asmundson ferences between varieties and strains are 1945). Strain 3 is a medium sized Broad inherited (Knox and Marsden 1944, As- Breasted Bronze, while strain 1 is a relamundson 1945) and at least in the case of tively small, narrow breasted, inbred breast width there is some variation which strain of Bronze, which is descended from is independent of weight of bird, although Bronze turkeys used by producers in Calihere, as in the case of length of keel and fornia about twenty years ago. Birds of shank, there is correlation with weight strain 1 have not been particularly se(Asmundson 1944). For length of shank lected for size or conformation and have Jaap (1938) has estimated that 25.3 per- not been crossed with Broad Breasted cent of the male and 39.0 percent of fe- Bronze at any time, hence, carry no genes male variance is caused by heredity. from that strain or variety. Some data are The present series of experimental mat- also given for Broad Breasted Bronze ings was started to obtain data on the strains 4 and 5 and the progeny from mode of inheritance of weight and confor- crosses of these and other strains. mation by using strains of Bronze turkeys The birds were hatched at two week inthat differ widely in weight and width of tervals from the latter part of March breast. The data were also analyzed sta- through the early part of May. Each year tistically to obtain estimates of the influ- the poults from three to five hatches were ence of differences between the sexes on used. They were floor-brooded with elecweight and the measurements used and trically heated hovers. At eight weeks of of weight on the latter. The paper by age they were moved to dirt yards. El-Ibiary and Jull (1948) points to the imFeed and water were before the birds all portance of such studies in order than an the time. An attempt was made to feed explanation may be found for the appar- rations that should give equivalent reent differences between the various pub- sults in successive years. Owing to war lished reports. conditions this attempt was not entirely successful since lower weights were atMATERIALS AND METHODS tained on the average in. 1944 and 1945 Most of the data presented in this paper than in 1943 and 1946 (Table 1). The birds were weighed and measured are for strains 1 and 3 and crosses be-
TABLE 1.—Means at 24 weeks of age
Birds in group No.
Group
Weight of bird, kilos.
Length of shank, cm.
Length of keel, cm.
Width of breast at point above lower surface of keel shown,, cm. 1 cm.
2 cm.
3 cm.
17 9 9 32
Females- -1943 4.54 15.35 16.14 5.56 15.97 6.01 16.03 5.93
14.72 15.67 15.47 15.12
2.96 3.50 3.68 4.23
4.18 5.04 5.32 5.86
5.22 6.37 6.74 7.25
Strain 1 F, (Str. 3 9 9 X S t r . l d V ) Fi(Str. 1 9 9 X S t r . $
17 20 23 44
Males— -1943 18.98 6.74 19.96 8.82 19.60 8.78 19.77 8.10
17.04 18.62 18.52 17.56
2.94 3.27 3.38 3.78
3.99 4.69 4.79 5.42
4.94 5.97 6.11 6.86
11 19 13 9 14 . 27 47
Females--1944 3.83 14.67 15.49 4.42 15.80 5.06 15.53 4.87 15.32 4.61 15.87 5.16 16.02 4.94
14.28 14.58 15.09 14.80 14.39 14.58 14.16
2.88 3.15 3.37 3.43 3.49 3.96 3.95
4.01 4.41 5.00 4.94 4.91 5.63 5.54
5.05 5.51 6.22 6.08 6.04 6.86 6.74
Strain 1 Fi 9 9 XStr. lcTc? Fi(Str. 3 9 9 XStr. left?) Fi(Str. 1 9 9 XStr. S
7 17 3 10 15 15 21
Males—-1944 6.01 18.67 18.99 6.56 18.40 6.09 19.74 7.21 18.75 6.42 19.40 7.07 20.06 7.33
16.19 16.34 15.97 16.63 16.01 17.14 16.19
2.71 3.11 3.13 3.25 3.10 3.52 3.65
3.83 4.36 4.47 4.61 4.53 5.07 5.21
4.73 5.51 5.53 5.83 5.62 6.38 6.50
Strain 1 Fi (Str. 3 9 9 XStr. l d V ) Fi(Str. 1 9 9 XStr. 3
15 7 23 60 42 56
Females--1945 15.03 4.17 15.76 5.23 15.87 5.12 15.72 4.86 16.28 5.15 15.97 5.08
14.47 15.17 15.02 14.82 14.81 14.22
3.14 3.74 3.46 3.62 3.69 3.88
4.51 5.34 5.00 5.18 5.24 5.56
5.67 6.70 6.37 6.55 6.70 6.96
Strain 1 Fi(Str. 3 9 9 XStr. lefc?) F, (Str. 1 9 9 XStr. Z
12 8 14 43 42 45
Males—-1945 18.81 6.28 19.64 8.14 19.03 7.40 19.43 7.04 20.02 7.54 19.51 7.27
16.67 17.55 17.14 16.83 17.03 16.21
2.93 3.58 3.30 3.31 3.56 3.68
4.10 5.06 4.61 4.72 5.09 5.26
5.12 6.43 5.84 5.97 6.45 6.63
Strain 1 Fi 9 9 XStr. Fi (Str. 3 9 9 Fi(Str. 1 9 9 F2 F, 9 9 XStr. Strain 3
36 17 28 8 82 12 28
Females--1946 15.54 4.30 15.91 4.85 16.25 5.39 16.04 5.37 15.97 5.06 16.13 5.47 16.26 5.56
14.25 14.84 15.10 15.15 14.82 14.80 14.58
3.13 3.24 3.47 3.46 3.49 3.60 3.83
4.59 4.86 5.24 5.34 5.30 5.38 5.74
5.94 6.32 6.78 6.83 6.77 6.88 7.38
22 10 17 8 49 18 25
Males-—1946 18.86 5.99 19.79 7.56 20.51 8.86 20.05 8.29 19.79 7.27 20.22 8.10 20.14 8.04
16.20 17.25 17.64 17.91 16.65 16.89 16.77
2.90 3.14 3.46 3.36 3.32 3.50 3.61
4.14 4.48 5.20 4.84 4.86 5.16 5.30
5.27 5.71 6.78 6.12 6.27 6.63 6.76
Strain 1 Fi 9 9 X S t r . Fi (Str. 3 9 9 F,(Str. 1 9 9 F2 Fi 9 9 XStr. Strain 3
Strain 1 Fi 9 9 XStr. F, (Str. 3 9 9 Fj (Str. 1 9 9 F2 Fi 9 9 XStr. Strain 3
lrf>c? XStr. I t i V ) XStr. 3
lcTc? XStr. lcfc?) XStr. 3d 1 d") 3d"d 1
1
lcfd XStr. lcfc?) XStr. 3
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Strain 1 Fi (Str. 3 9 9 X S t r . lcfc?) Fi (Str. 1 9 9 XStr. 3o'er 1 ) Strain 3
GENETICS OF WEIGHT AND CONFORMATION IN TURKEYS
at 24 weeks as described before (Asmundson 1944). RESULTS OF CROSSING STRAINS 1 AND 3
breast increase after the birds are 24 weeks old. In general, the length of shank varied with body weight but there were minor exceptions; such minor exceptions also occurred in the data for crosses between Bronze strains 2 and 3 (Asmundson 1945). The Fi progeny tended to have shorter shanks that the birds of strain 3. Out of the 16 Fi groups, four had longer shanks than the strain 3 birds. Three of these four (see males 1943, 1945, 1946) were larger than corresponding strain 3 birds, while the one group of females in 1943, which were smaller than the corresponding strain 3 birds, did not have significantly longer shanks, since the difference was 0.11 +0.15 and therefore less than its standard error. The F2 progeny and those obtained by backcrossing on strain 1 males had shanks that were in most cases shorter than those of all others except strain 1. These facts again suggest that autosomal genes determine length of shank, that longer is dominant to shorter shank length and that while general size factors largely determine the length of shank, other genes may also have an effect. It may be pointed out in this connection that the "short" gene in turkeys, an autosomal recessive, also reduced body weight (Asmundson 1944a). Other evidence presented below also shows that special size factors probably play a very minor role in determining length of shank. Length of the keel of the sternum. The keels of the birds of strain 1 were not consistently shorter or longer than those of strain 3. The Fi progeny had, with the exception of the one small group of males in 1944, consistently longer keels than the parental strains. The progeny of back crosses on the parental strains also had consistently longer keels on the average than the parental strains. The F 2 progeny,
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The averages at 24 weeks are presented in Table 1. The birds of strain 1 were consistency smaller than those of strain 3, and differed from the latter in all measurements, except length of keel. The analyses of variance of the data (Table 2) shows that there were in each case statistically significant differences. Weight of bird. The Fi progeny frequently equalled or exceeded the average weight of the larger (strain 3) parent. The Fi from reciprocal matings did not differ consistently, hence weight is here determined by autosomal genes. If weight at 24 wee.ks were determined by sexlinked genes, the female progeny of strain 1 females X strain 3 males should outweigh those from the reciprocal cross, while this was only so in one of the four years. The progeny of the backcross on strain 3 males weighed slightly more than the birds of strain 3 except in the case of the females in 1946. None of the differences were statistically significant. On the other hand the progeny of the backcross on strain 1 males were (with one doubtful exception of 3 Fi males in 1944) intermediate in weight between the Fi and strain 1. The F 2 progeny also weighed less than the Fx progeny. These data show, beyond reasonable doubt, that large size, as measured by weight, is dominant to small size in this cross. Length of shank. The smaller birds of strain 1 had uniformly shorter shanks (tarsometatarsi) on the average than those of strain 3. Since the tarsometatarsal bones stop growing at about 20 weeks (Kodinetz, 1940; Asmundson and Lerner, 1942) the length of shank is about the same as that of the mature bird, while body weight, length of keel, and width of
697
698
V. S. ASMUNDSON TABLE 2.—Mean squares—for 24 week old birds. All values of F are significant (see footnotes)
Source of variance
Degrees of freedom No.
Body weight, kilos
Length of shank, cm.
Width of breast at point above lower surface of keel shown, cm.
Length of keel, cm.
1 cm.
2 cm.
3 cm.
66 3 63
Females—1943 .65 0.39 7.91 5.32 .30 0.15 26. 34.42
0.47 2.06 0.40 5.15
0.93 6.18 0.68 9.07
0.74 10.56 0.27 38.55
1.05 15.46 0.37 42.33
Total Between means of groups Within groups
103 3 100
Males—1943 1.33 0.55 17.44 3.40 .85 0.46 20.58 7.34
1.11 12.29 0.77 15.90
0.21 3.31 0.12 28.03
0.49 9.03 0.23 39.34
1.03 15.83 0.59 26.95
Total Between means of groups Within groups F2
139 6 133
0.68 1.19 0.62 3.08
0.47 3.30 0.34 9.71
0.62 6.61 0.35 18.89
0.76 8.05 0.44 18.30
Total Betwen means of groups Within groups F2
87 6 81
0.75 2.15 0.64 3.35
0.19 1.16 0.12 9.77 .
0.39 2.58 0.23 11.28
0.61 4.18 0.35 11.92
Total Between means of groups Within groups F3
202 5 197
Total Between means of groups Within groups F3
163 5 158
Total Between means of groups Within groups
210 6 204
148 6 142
Females—1944 .57 0.49 3.16 3.39 .45 0.36 7.05 9.42 Males—1944 1.67 0.96 1.06 4.27 .10 0.71 10.42 5.99 Females—1945 .33 0.35 2.69 3.92 .27 0.26 9.95 15.08
1 2 3 4
Significant Significant Significant Significant
values of F:P=.05, values of F : P = . 05, values of F : P = . 05, values of F:P=.05,
0.18 1.56 0.15 10.40
0.39 3.02 0.32 9.44
0.36 4.40 0.26 16.92
0.75 4.76 0.63 7.56
0.14 1.48 0.10 14.80
0.27 3.53 0.17 20.76
0.44 5.89 0.26 22.65
Females—1946 .38 0.25 5.68 1.92 .23 0.20 24.89 9.60
0.43 2.51 0.37 6.78
0.10 1.47 0.06 24.50
0.29 4.03 0.19 21.21
0.39 6.17 0.22 28.05
Males—1946 1.50 0.66 17.20 5.65 .84 0.45 20.47 12.56
1.03 5.43 0.84 6.46
0.11 1.22 0.06 20.33
0.28 3.58 0.14 25.57
0.47 6.28 0.23 27.30
.74 4.68 .61 7.65
p-4
Total Between means of groups Within groups F4
0.49 3.73 0.41 9.10
9 9 9 9
9 9 9 9
Males—1945 0.66 4.06 0.56 7.25
-2.75, -2.17, -2.26, -2.14,
9 9 9 9
9 9 9 9
-4.11, -2.94, -3.11, -2.89,
cfc? d'c? cfc? cTc?
-3.98. -3.04. -3.14. -2.93.
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Total Between means of groups Within groups
GENETICS OF WEIGHT AND CONFORMATION IN TURKEYS
These results are in good agreement with those obtained before (Asmundson 1945) when crosses were made between strains 3 and 2, the latter an improved strain selected for good conformation but without any admixture of Broad Breasted Bronze in its ancestry. RESULTS WITH OTHER BROAD BREASTED BRONZE The question might well be asked as to whether the results obtained when strain 3 is crossed with strain 1 are typical of those which would be obtained if other broad breasted strains were used. Data obtained in 1946 are available on this point for two additional strains (Table 3). Of the two, strain 4 are straight Broad Breasted Bronze, while strain 5 are of mixed origin, but the birds conform approximately to the broad breast standard by having a width of about 3§ inches at If inches above the keel. There were statistically significant differences between the various groups (see Table 5 below), particularly strain 4 and 5. The male birds in strain 4 weighed about the same as those in strain 3 while the females of strain 4 were slightly heavier. Strain 5 birds were smaller, had shorter shanks and a shorter keel than the birds in strains 3 and 4. The birds of strains 3 and 5 did not differ significantly in width of breast, while both had narrower breasts than those in strain 4. Thus, for the females of strains 3 and 4 the difference in width of breast at 1 cm. above the keel of 0.30 cm. is statistically highly significant (t = 3.00, p = <01). The data in Table 3 show that when males from strain 4 were crossed with hens of strains 1 and 5, the progeny were wider breasted than the progeny obtained from strain 3 males mated to strain 1 and 5 females. The progeny from strain 5 females X strain 3 or 4 males were wider
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however, did not consistently have longer or shorter keels than the parental strains. With one exception (males 1944) the F 2 progeny had shorter keels than the corresponding Fi progeny. These differences cannot be attributed to differences in weight, since, for example, the Fx progeny did not in all cases weigh on the average more than the birds of the parental strains. The data for length of keel suggest that the parental strains had different dominant genes for length of keel and that these act like complementary genes in such a way as to produce longer keels in the Fi progeny (AaBb>AAbb or aaBB). The recombinations obtained in the F2 again produced shorter keels but not quite so short as those of the parental strains. These results suggest the dominance of genes for long keel over those for short keels. There is no indication of sexlinked genes but in view of the absence of consistent differences between the parental strains, the evidence on this point is not conclusive. Width of breast. The two strains differed significantly in width of breast with the birds of strain 3 having wider breasts that those of strain 1. The Fi progeny were in all cases intermediate between the parental strains and there were no consistent differences between the Fi progeny from reciprocal crosses, hence the differences in breast width are determined by autosomal genes. There is no indication of dominance. While width of breast obviously varies to some extent with weight of bird, there is considerable independent variation, otherwise width of breast would follow differences in weight more closely. It is also apparent that more than one pair of genes is involved, since the backcross progeny were intermediate between the ¥1 progeny and the parents.
699
700
V. S. ASMUNDSON
TABLE 3.-—Averages for 24-week-old Bronze turkeys in 1946. Comparisons of strains 3 and 4 Weight,
Description of group
No.
Strain 4 Strain 5 Hens* X Strain 3 cfc?1 Hens* X Strain 4c?
23 41 22 24 18 40 28
Females 5.68 4.83 5.42 5.67 5.52 5.77 5.67
Strain 4 Strain S Hens* X Strain 3 d V Hens* X Strain 4c? cf HenstXStrain3cTcr HenstXStrah^cTc? Str. 3 9 9 X Str. 4c? d"
21 32 23 13 19 37 21
8.07 6.65 7.91 8.31 8.32 7.97 8.62
Length of shank, cm.
Length of keel, cm.
Width of breast 1 cm. above keel, cm.
16.33 15.88 16.22 16.23 16.09 16.28 16.50
14.86 13.77 14.84 15.08 14.72 14.65 14.73
4.13 3.76 3.65 3.85 3.72 4.02 3,97
20.08 19.36 20.16 20.20 20.21 20.10 20.42
16.86 15.45 16.81 17.15 17.22 16.88 16.73
3.91 3.58 3.46 3.67 . 3.55 3.66 3.88
Males
breasted than those from strain 1 females mated to strain 3 or 4 males (details not shown in Table 3, but compare line 5 under females and under males in Table 3 with line 4 under "females-1946" and "males-1946" in Table 1). The width of breast of the progeny thus varies according to the width of breast of the parents as one might expect, since there is no dominance of wide over narrow breast (see above). The data further show that strain 4 males, when crossed with other strains, not only produced wider breasted progeny than strain 3 males, but also larger progeny at 24 weeks. These results indicate that the width of breast of the progeny of any two different strains of turkeys may be expected to vary according to the width of breast of the parental strains. On the other hand, weight of bird cannot be accurately predicted from the weights of the strains crossed, which agrees with results reported before when different varieties were crossed (Asmundson 1942) although in most cases the progeny approached or exceeded the weight of the larger parents
at 24 weeks of age. However, when Knox and Marsden (1944) crossed a small variety (Beltsville Small White) with large Broad Breasted Bronze, the progeny were intermediate. GENETIC VARIATION WITHIN THE BROAD BREASTED BRONZE
The data for strains 3 and 4 were further analyzed as shown in Table 4. The data for all male and female progeny were first separately totaled and averaged. From the averages a correction factor was calculated. The data for each male were then recalculated as follows: weight divided by 1.47; length of shank divided by 1.24; length of keel divided by 1.14; width of breast at 1 cm. above the keel multiplied by 1.05. The number of progeny from each of the 21 dams varied from 2 to 14 and there were two or three dams (mates) to each of the eight sires. The differences between the means of full sib families (dams) were statistically highly significant, while those between sires were not.
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* Hens out of strains 1 and 3—Fis or backcrosses on strain 3. f Hens of strains 1 and strain 5.
GENETICS OF WEIGHT AND CONFORMATION IN TURKEYS
701
TABLE 4.—Mean squares/or 24-week-old Broad Breasted Bronze turkeys in 1947. Combined data, with those for males corrected to those for females
Source of variation
Degrees of freedom
Weight
Length of shank
142 7 135 13 122
0.509 1.539 0.456 1.581 0.336 0.972 4.720
0.260 0.957 0.224 0.896 0.153 1.068 ,5.874
Total Between sires Within sires Between dams Between full sibs F* value for sires F* value for dams
Length of keel 0.540 2.014 0.463 2.170 0.282 0.928 7.710
Width of breast at 1 cm. above the keel 0.105 0.531 0.083 0.393 0.050 1.351 7.892
' The 5 % value of F is, for sires 2.85, for dams 1.81; the 1% value of F is, for sires 4.46, for dams 2.36 portant since they point to the need for constant selection to maintain whatever standards are adopted. Moreover, the data show the importance of careful selection of dams as well as sires. Such a conclusion of course, also comes from the finding that the characters dealt with are determined by autosomal genes. RELATION OF CONFORMATION TO SEX A very high percentage of the total
TABLE 5.—Mean squares. Upper part (A) based on data for 24-week-old males and females in 1946 {Table 1); lower part (B) based on 1946 data used in Table 3, plus those in the same year for Strain 3 {means in Table 1) Source of variation
Degrees of freedom
Total Between sexes Within sexes Between groups Within groups F (between sexes) F (between groups)
359 1 358 12 346
Total Between sexes Within sexes Between groups Within groups F (between sexes) F (between groups)
414 1 413 15 398
Percentage of total' variation accounted for by differences between Sexes A Sexes B Groups A Groups B
Length of keel
Width of breast 1 cm. above keel
4.08 1,312.73 0.42 3.78 0.30 347.28 12.60
1.76 389.98 0.68 3.97 0.57 98.23 6.96
0.11 1.23 0.10 1.35 0.06 0.91 22.50
4.07 1,516.77 0.41 102.87 0.35 14.74 293.91
1.93 424.80 0.90 34.65 0.69 12.26 50.21
0.14 4.73 0.13 0.88 0.11 5.38 8.00
89.71 89.93 2.94 1.47
61.36 53.37 6.25 10.88
9.09 7.14 36.36 14.29
Weight
Length of shank
Part A 2.38 552.72 0.85 11.36 0.48 48.65 23.67 PartB 2.38 589.08 0.96 45.44 0.76 12.96 59.79
64.29 59.66 15.55 8.40
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The highly significant differences between dams (Table 4) show that there is genetic heterogeneity within Broad Breasted Bronze supposedly free from admixture with other varieties. The fact that the differences are between full sib (sister-brother) families has no special significance. A larger sampling with males selected at random undoubtedly would reveal statistically significant differences between sire families. The results are im-
702
. V. S. ASMTJNDSON
recommended by Bird (1945). Apparently the fact that the measurements would thereby be taken at a greater distance above the keel in males than in females did not eliminate the difference between the sexes observed when the measurements are made at a fixed point above the keel (see Tables 1 and 3). Sex differences have also been observed in the growth of bones and muscles of younger birds (Asmundson and Lerner 1940). RELATION OF MEASUREMENTS TO WEIGHT
Length of shank, length of keel and width of breast at 1 and 5 centimeters above the keel are known to be positively correlated with weight of bird (Asmundson 1944). As a first step to determine relationships for the birds in strains 1 and 3 and their crosses, the zero order correlations were calculated for the largest series available, the 24 week-old females in 1946, and the males in that same year (Table 6). All of the coefficients of correlation based on the total variation and the variation within groups were statistically significant except between length of shank and width of breast for within groups. Most of the coefficients between means of groups for females and for males were not significant. It has been pointed out above that males are larger—that is, weigh more, have ionger shanks and longer keels— than females of the same age and similar ancestry. The males also have deeper bodies, Asmundson (1944), Bird (1945). From this it would be expected that combined uncorrected data for males and females might give a negative correlation for length of shank, length of keel and even weight with width of breast. The sex differences would make any conclusion drawn from correlation coefficients based on the total variation in such data for
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variation (Table 5) in weight, length of shank, and length of keel, or about 60, 90 and 60 percent respectively is accounted for by differences in sex. The figures for length of shank are in good agreement with the 91 percent reported by Jaap (1938a). Sex differences account for less than 10 percent of the variation in breast width, while differences between groups account for a higher percentage but less than variation within groups. The percentage of the total variation accounted for by differences between groups and within groups is in each case less for weight and length of keel than for width of breast, while it is least for length of shank. The differences between the sexes were, with the exception of width of breast (in Part A of Table 5), highly significant. These, differences in weight, length of shank, and length of keel of 24-week-old males and females have long been recognized, while little attention has been paid to the difference in width of breast. Nevertheless, an examination of tables 1 and 3 shows that the difference in width of breast is as consistently expressed as the other differences—the males being narrower than the females. Since the difference between sexes in width of breast was not statistically significant for one of the two groups in Table 5, it seemed advisable to further analyze the data in Table 1. For each group the average difference was calculated for width of breast at 1 cm. above the keel by subtracting the width of breast of the males form that of the corresponding group of females. The average difference thus obtained between the 24 pairs of groups was .2025, which, using the method of Fisher (1932) proved to be statistically highly significant (t = 8.33, p = <.01). This agrees with El-Ibiary and Jull (1948) who measured width of breast at a point above the keel one fifth of the depth as
703
GENETICS OF WEIGHT AND CONFORMATION IN TURKEYS TABLE 6.—Coefficients
of correlation and regression 24-week-old males and females, 1946 Weight and
Degrees Length of shank of freedom Regression
Length of shank and Width of breast a t 1 cm. above the keel
Length of keel Regression
Length of keel
sion
Width of breast at 1 cm. above keel
Length of keel a n d width of breast at 1 cm. above keel Regression
Regression
Regres- sion
Total Between groups Within groups
210 6 204
.650 .981 .424
.47 .57 .40
. 703 .680* .754
.75 .45 .96
.633 .906 .431
Females .33 I .440 .46 .709 .23 | .378
.58 .91 .51
.345 .863 .127
.43 .75 .33
.238 .366 .204
.12 .28 .08
Total Between groups Within groups
.48 6 142
.793 .982 .674
.53 .56 .49
.785 .832 .805
.65 .47 .81
.644 .827 .485
Males .17 ) .606 .22 .743 .13 I .564
.76 .73 .77
.468 .906 .174
.19 .42 .06
.352 .462 .319
.11 .22 .08
Total Between sexes Between groups Within groups
359 1 12 346
.900 1.000 .985 .585
.909 .998 .802 .780
Males and females .852 1.000 .732 .491
.211 .997 .820 .435
038 -.997 .409 .255
.050 .997 .085 .550
males and females useless, hence the last part of Table 7 was not calculated until after the paper by El-Ibiary and Jull (1948) appeared. The correlation between means of sexes has no significance since n - 2 = 0 (Fisher 1932). It will be observed, however, that the correlation between means of sexes for width of breast with weight, length of shank and length of keel is in each case negative while the other coefficients are positive. All of the coefficients for between groups and within groups are positive and all of the latter are statistically significant.
Sampling might account for some of the differences in the coefficients of correlation based on total variation, in Table 6, from those reported by El-Ibiary and Jull (1948). Accordingly correlations were calculated (Table 7) for three groups of Broad Breasted Bronze in 1946. One of these three groups comprised strain 3 which was also included in the data, used to calculate Table 6. Since there were three groups, only the coefficients based on the total variation are shown in Table 7 for the females and for the males but for the combined data the same coeffi-
TABLE 7.—Coefficients of correlation based on body weiglits and measurements of 24-week-old Broad Breasted Bronze only ' Source of variation
Degrees of freedom
Weight and Weight and Weight and W * Length of Length of shank and shank and keel and length of length of width of length of width of width of shank keel breast* keel breast breast
Total
78
.571
Females .805
.430
.599
.090
.338
Total
66
.723
Males .733
.447
.543
.168
.155
145 1 4 140
.980 1.000 .923 .659
Males and females .915 -.016 1.000 -1.000 -.158 .462 .783 .426
.861 1.000 -.069 .581
-.219 -1.000 .304 .116
-.679 -.999 .719 .235
Total Between sexes Between groups Within groups
' Italics indicate significant values at p = .(ji.
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Italics indicate significant values at £ = . 0 1 (Fisher, 1932).
704
V . S. ASMUNDSON TABLE 8.—Coefficients of partial correlation with variation in body weight eliminated. Based on data in Table 6 Measurements correlated
Total
Shank and keel Shank and width Keel and width
-.030 -.112 -.376
Shank and keel Shank and width Keel and width
-.044 -.092 -.324
Between means of groups Females .279 -.314 -.806 Males -.706 .884 -.725
Within groups
.098 -.068 -.204 -.049 -.238 -.138
significant and between groups, where it is positive. For both males and females, the coefficient based on the total variation for length of keel with width of breast is negative and statistically significant. These results are consistent with those previously obtained (Asmundson 1944) in showing that, when variation in weight is eliminated, there is no consistent statistically significant relation between the length of shank and the length of keel nor between the length of shank and width of breast, while length of keel and width of breast are negatively correlated. Moreover, they lend no support to the conclusion of El-Ibiary and Jull (1948) that for good breast conformation birds should be selected for relatively short shank and long keel. For the 24-week-old males and females in 1946 (Table 1) the regression of the three measurements (length of shank, length of keel, and width of breast) on weight was calculated (Table 6). The regression coefficients based on variation within groups were then used to calculate corrected measurements for each of the 211 females and 149 males by using the difference in weight between the individual and the mean weight of the entire population of females and of males respectively. The analyses of the data so obtained are in Table 9. These data show that when the shank length was corrected
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cients are presented as in Table 6. Here the coefficients between means of sexes again are negative for width correlated with weight, length of shank or length of keel. These same coefficients based on total variation are also negative but only the last (length of keel correlated with width of breast) is statistically significant. Again the coefficients based on variation within groups are all positive, although two (width with length of shank and with length of keel are not statistically significant. The data in these tables show fairly conclusively that the correlation between weight, length of shank, length of keel, and width within sexes is positive. These coefficients of correlation are usually statistically significantly except between length of shank and width of breast and in some cases (Table 7) length of keel and width of breast. The negative correlation between length of shank and width of breast obtained by Ibiary and Jull apparently stems basically from lumping together the data for the larger, narrower breasted males with those for the females. A further statistical analysis of the data was made in order to obtain evidence about (1) the extent to which length of shank, length of keel, and width of breast are correlated independent of weight and (2) to find out whether significant differences would remain between groups after these measurements were corrected for differences in the weight of the birds. From the values of r in Table 6, the coefficients of partial correlation were calculated, with the effects of differences in weight eliminated (Table 8). The coefficients of partial correlation for length of shank with length of keel were not significant. This was also true for length of shank with width of breast except in the case of the males for within groups, where the coefficient is negative and statistically
GENETICS OF WEIGHT AND CONFOKMATION IN TURKEYS TABLE 9.—Analyses of variance for 24-week-old females and males in 1946, based on measurements corrected for regression on weight
210
Between means of groups Within groups F
6 204
Total
148
Between means of groups Within groups F
142
Females 0.17 0.26 0.24 0.16 1.50
Width of breast 1 cm. above keel 0.06
3.03 0.18 16:83 Males 0.30 0.48
0.53 0.05 10.60
0.34 0.29 1.1
0.51 0.04 12.75
8.37 0.15 55.61
0.64
for regression on weight, there was no longer a statistically significant difference in the length of shank of the various groups. The implication is clear that the differences in the length of shank of the two strains (1 and 3) and the progeny obtained by crossing them are due primarily to differences in weight. On the other hand significant differences in length of keel and width of breast remain after thus correcting for differences in weight. These results indicate that it would be difficult to select for change in length of shank without changing weight of bird, or vice versa. This indeed was what Lerner (1943) found with White Leghorn chickens. Length of keel and width of breast should respond to selection and corresponding changes in weight should not necessarily follow. DISCUSSION
The data in this paper on inheritance of body weight and width of breast are in good agreement with earlier results for Bronze (Asmundson 1945) in that large size as measured by body weight at 24 weeks of age is dominant to small size, while there is no dominance of wide over
narrow breast, the Fi progeny being intermediate. When other varieties were crossed (Asmundson 1942) the results for the most part agreed with those for crosses between different strains of Bronze, the Fi progeny weighing about as much as the larger parent, or more than either parent. Knox and Marsden (1944) reported different results for a cross between Bronze and Beltsville Small White, the Fi progeny being intermediate and closer to the smaller parent, thus indicating dominance of genes for small size. They also reported that the length of shank of the Fi progeny was intermediate and closer to the small parent which would be expected in view of the fact that length of shank appears to be determined largely by general size factors. The results reported in this paper indicate that for both shank and keel, long is dominant to short. Our results indicate that weight and conformation are determined by autosomal genes. In general, our results for inheritance of body weight and length of shank appear to agree well with the conclusion of Knox and Marsden that they are typical of quantitative characters. The results in this paper for length of keel and width of breast cannot be compared with these of Knox and Marsden for breast type. Regardless of differences in dominance, the evidence available indicates that weight and conformation are inherited and therefore subject to change by selection. The question still remains as to the relation between weight and depth of body, length of shank (tarsometatarsus) or other long bones of the extremities, length of keel and width of breast. In general the heavier birds have longer shanks, but the bones are shorter per unit of weight in larger than in smaller birds, as pointed out by Asmundson and Lerner 1942. (Bird (1945) has reported an exception—the larger Broad Breasted
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Total
Length of keel, cm -
70S
706
V. S. ASMTJNDSON
the coefficients been calculated separately for each sex, it is to be expected that such results would not have been obtained. Our results (Tables 6 and 7) clearly indicate that when data for males and females are combined, the sample used will also determine the size of the coefficient and whether it is positive or negative. The facts stated above; namely, that males are larger and have narrower breasts than females clearly imply that when the uncorrected data for males and females are combined, some (but not all) samples of populations may be expected to show significant negative correlation between width of breast and any measure of size such as weight, depth of body, length of shank and length of keel. The implications of the various relationships mentioned above indicate that when birds are selected for breeding purposes, length of shank may be ignored or considered, with body weight as a measure of size. For example, selection for shorter shank and heavier body weight would cancel each other and is therefore impractical. On the other hand, there is apparently sufficient variation in length of keel and in width of breast independent of variation in weight to permit of changing the relationships between these through selection. Normally, however, an increase in width of breast or in length of keel will result in an increase in body weight; also selection for a wider breast without an increase in weight will normally result in a shorter keeled bird and vice versa. Some selection for moderate length of keel would therefore seem advisable when birds are selected for width of breast but the statement of El-Ibiary and Jull (1948) that selecting birds for long keels would result in birds otherwise "excelling in roundness of breast" does not appear to be justified by the available facts. Rather the facts suggest that the
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Bronze had shorter tibias than the Standard Bronze males). This is well illustrated by the data in Tables 1 and 3. The females have shorter shanks than the males but a simple calculation will show that per unit of body weight the males have shorter shanks than the females. It is obvious that the average differences in length of shank of the males or of the females considered separately are less than the differences in their weights. This indicates that the term, relatively short shank, which is based on the length of the shank in terms of weight, is meaningless. Thus the Broad Breasted Bronze birds of strain 3 have a longer shank than the narrower breasted birds of strain 3 (Table 1) but, being heavier, the former may be said to have relatively shorter shanks. No harm would be done by the use of this phrase if it were not inferred that there was some causal relation between width of breast and relative length of shank. Such a relationship has been inferred from weights and measurements by Jaap (1938) and Bird (1945). When these inferences are subjected to statistical analysis, it is found that the various measurements are positively correlated with weight and with each other. However, when the effect of weight is eliminated by use of the coefficient of partial correlation, it is found that length of shank is not usually correlated with length of keel nor with width of breast. On the other hand there is a low but significant negative correlation between length of shank and width of breast. These results and the conclusions drawn from them are diametrically opposed to those of El-Ibiary and Jull (1948). The negative correlation obtained by them for length of shank and width of breast is apparently primarily due to basing the calculation of the coefficient of correlation on the combined, uncorrected measurements for both males and females. Had
GENETICS OF WEIGHT AND CONFORMATION IN TURKEYS
selection should be simply for width or roundness of breast, if greater width or roundness is the objective. Whether such selection would result in any change in the length of the bones should perhaps be considered an open question in view of the data published by Bird, but all other evidence argues against such a result. SUMMARY
tween the parental strains in width of breast; there was no difference in the width of breast of the progeny from reciprocal matings. The progeny from backcrosses were in each case intermediate between the Fis and the parental strain. Width of breast is thus determined by nondominant autosomal genes. The progeny of strain 4 and strain 3 males, both broad breasted, were compared. Strain 4 birds had wider breasts than those in strain 3. The breast width of the progeny varied with the width of breast of the parents, while body weights did not. Significant differences in weight, length of shank, length of keel, and width of breast were found between full sib families of Broad Breasted Bronze. Significant sex differences were observed with the males being larger (as measured by body weight, length of shank, length of keel) and narrower breasted. The percentage of the total variation accounted for by differences in sex accounted for nearly 90 percent for length of shank, about 60 percent for weight and for length of keel, and less than 10 percent for width of breast. The coefficients of correlation for two partly overlapping populations of 24week-old males and females in 1946 were calculated. The length of the bones and width of breast were positively correlated with weight. When the influence of weight was eliminated there was no correlation (based on the coefficient of partial correlation) between length of shank and length of keel, nor was there any consistent correlation between length of shank and width of breast, while length of keel and width of breast were negatively correlated. When the measurements were corrected for weight by using the regression coefficient for within groups, the difference between means of groups was insignificant
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Two strains of Bronze (Nos. 1 and 3) which differed in weight and width of breast were crossed. Fis, F2S, and the progeny of backcrosses to the males of the parental strains were raised. All birds were weighed and measured (length of left shank, length of keel, width of breast) at 24 weeks of age. The Fi progeny equalled or exceeded the larger Broad Breasted Bronze parent and there was no difference in the progeny from reciprocal matings. The F2 progeny weighed less than the Fis; the progeny .from the backcross on the larger parent equalled the parental weight, while those from the other backcross were intermediate between the Fis and the smaller parental strain. These results show that heavy (large) is dominant to light and that weight here is determined by autosomal genes. The results for length of shank were, in general, similar to those for weight although some apparent differences occurred. The two strains did not differ consistently in length of keel, while the Fi and backcross progeny had, with one doubtful exception, longer keels than the parental strains. The F2s had shorter keels than the Fis but they did not have consistently longer keels than the parental strains. These results suggest that the parental strains had different dominant complementary genes. The Fi progeny were intermediate be-
707
708
V. S. ASMUNDSON
for length of shank but remained statistically highly significant for length of keel and for width of breast. I t is concluded from these results that selection for change in length of shank would result in a change in weight, whereas such would not necessarily be the case when length of keel or width of breast are changed by selection. REFERENCES
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Asmundson, V. S., 1942. Crossbreeding and heterosis in turkeys. Poultry Sci. 21: 311-316. Asmundson, V. S., 1944. Measuring strain differences in the conformation of turkeys. Poultry Sci. 23:21-29. Asmundson, V. S., 1944a. Inherited shortening of the long bones in the turkey. Jour. Heredity 35: 295-299. Asmundson, V. S., 1945. Inheritance of breast width in turkeys. Poultry Sci. 24: 150-154. Asmundson, V. S., and I. M. Lerner, 1940. Growth of turkeys. I. Influence of strain, sex, and ration. Poultry Sci. 19:49-54. Asmundson, V. S., and I. M. Lerner, 1942. Growth
of turkeys. II. Relative growth of the Tarsometatarsus. Poultry Sci. 21: 505-510. Bird, S., 1945. Determination of fleshing characteristics in market poultry. II. Turkeys. Scientific Agric. 24: 481-488. El-Ibiary, H. M., and M. A. Jull. 1948. Criteria and genetic variation of live body conformation in turkeys. Poultry Sci. 27: 40-52. Fisher, R. A., 1932. Statistical methods for research workers. 4th edit. Oliver and Boyd, Edinburgh. Jaap, R. G., 1938. Estimating the influence of heredity on the tarso-metatarsal length of the domestic turkey. Proc. Oklahoma Acad. Sci. 19: Jaap, R. G., 1938a. Body conformation of the live market turkey. Poultry Sci. 17: 120-125. Knox, C. W., and S. J. Marsden, 1944. The inheritance of some quantitative characteristics in turkeys. Jour. Hered. 35: 89-97. Kodinetz, G., 1940. Beitrag zur Kenntnis der Rasse und der Entwicklung des Zagioraner Truthuhnes (Meleagris gallopavo). Zeitschr. f. Tierzucht. u. Zucht.-biol. 47:140-165. Lerner, I. M., 1943. The failure of selection to modify shank growth ratios of the domestic fowl. Genetics 28: 80-81.