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The Relationship Between Color Phenotypes and the Presence of Black Melanin in the Abdomen of Broiler Chickens: Study 2
The Relationship Between Color Phenotypes and the Presence of Black Melanin in the Abdomen of Broiler Chickens: Study 2 C. M. HUNTSMAN, F. N. JEROME AND E. S. SNYDER Poultry Department, Ontario Agricultural College, Guelph, Ontario, Canada (Received for publication October 9, 1959)
I
ens in addition to the phenotypes classified in the first study. The major consideration in arranging the matings of the breeding stock was to obtain progeny in which a segregation of eight phenotypes occurred with the same expected frequency within each phenotype. The eight desired phenotypes were: IEB, IEb, IeB, Ieb, iEB, iEb, ieB and ieb. In order to obtain this segregation, a male heterozygous for dominant white and exhibiting black flecks on the body and a ghost barring pattern, was crossed with Columbian Rock females. From the progeny produced, a number of males with a pattern similar to their sire, was selected and mated to unrelated Columbian Rock females to produce the progeny from which the data were gathered. The selection of these particular males gave assurance that the genotypic mating was, Ii Ee Bb $ $ X ii ee b- 9 9 The frequencies occurring in the segregated phenotypes verified the genotypes listed above. In addition, it should be mentioned that the genotype of the paternal grandsire was verified to be Ii Ee Bb Ss. As a result of this genotype a certain frequency of the s gene carried through to the final progeny. Before presenting the data, it may be advisable to describe how the classification for plumage color phenotype was carried out. The iEB and iEb phenotypes are easily recognized at hatching time. Most of the ie phenotypes are distinguished at hatching time by the fact that there are
882
Downloaded from http://ps.oxfordjournals.org/ at Simon Fraser University on May 29, 2015
N THEIR original study (Huntsman, Jerome and Snyder, 1959) the authors reported on the relationship of four color phenotypes to the deposition of black melanin in the abdomen of broiler chickens. The four phenotypes classified were, extended black, barred (EB); extended black, non-barred (Eb); restricted black, barred (eB); and restricted black, nonbarred (eb). It was found that the combination of extended black and barring tended to decrease the incidence of melanin deposition in the abdomen below the average for all phenotypes. In contrast to this, the combination of restricted black and barring tended to increase the frequency of this deposition above the average for all phenotypes. The deposition of melanin was found to occur more than twice as frequently in females as in males. These results substantiated those reported by Jaap (1955) and again by Jaap (1958). The data presented by Huntsman et al. showed that in some comparisons extreme interactions occurred between sex and genotype as measured by the incidence of deposition of melanin. For example, when the phenotype was restricted black there was a great variation in frequency between the sexes. When the phenotype was extended black the variation between the sexes was greatly reduced. The study to be reported here was carried out in order to investigate the effect of dominant white on the deposition of melanin in the abdomen of broiler chick-
m
ABDOMINAL BLACK
TABLE 1.—Prevalence and degree of abdominal melanin deposition in relation to sex
Sex
9 9
No. of birds 669 612
Degree of pigmentation and percentages None
Trace
Distinct
69.4 30.7
13.7 18.0
16.9 51.3
of gold or silver could be assessed accurately only in certain combinations. These combinations occurred only in the female progeny and were genotypically ii ee b-, ii ee B- or ii Ee b-. In the last mentioned genotype the females carrying gold had gold lacing on the neck, those carrying silver had silver lacing on the neck. A total progeny of 1281 individuals, produced from four weekly hatches, were reared to approximately 11 weeks of age, at which time they were killed and examined for the presence and degree of melanin deposition. In Table 1, data are presented to show the relative incidence of the character within the sexes. The data presented above agree well with those from former work and add further evidence to show that females carry a higher frequency of abdominal melanin deposition. One of the main objectives of this study was to observe the effect of dominant white on the incidence of this character. The data pertinent to this phase of the study are presented in Table 2. From the data presented in Table 2 it
TABLE 2.—Prevalence and degree of abdominal melanin deposition in relation to dominant white and its allele within sex Degree of pigmentation and percentages Sex
Genotype
1
d'c?
Ii ii
9 9
Ii ii
No . of birds None
Trace
Disl inct
308 361
82.1 58.4
14.0 13.6
3.9 28.0
313 299
40.2 20.7
21.1 14.7
38.7 64.6
Downloaded from http://ps.oxfordjournals.org/ at Simon Fraser University on May 29, 2015
no black flecks on the body but black pigment is present in the primary wing quills. Any mistakes originating through the nonappearance of black in the quills can be corrected when the birds grow tail and wing feathers. Barring and non-barring can also be recognized at this time in these particular birds. The IE and Ie phenotypes can be distinguished at hatching time by the fact that although both types lack black pigment in the primary wing quills, the IE phenotype will almost invariably exhibit at least a few strands of black down somewhere on the body while the Ie phenotype will not. The chief difficulty encountered was in the classification of barring and non-barring in the presence of dominant white. Certain individuals carried almost pure white plumage and could not be classified for the presence or absence of barring. However, many of the dominant white phenotypes exhibited a creamish or brownish shade of color at 9 weeks of age and it served as a suitable background for the barred and non-barred characters. In the IE phenotypes there were sufficient black areas on the feathers of certain individuals, to denote whether barring was present or absent. All classifications involving barring and non-barring in the presence of dominant white were carried out independently by two of the authors. The few birds on which there was disagreement or doubt were classed as unidentified. The presence
884
C. M. HUNTSMAN, F. N. JEROME AND E. S. SNYDER TABLE 3.-
-Prevalence and degree of dominant white and
melanin deposition in relation to combinations of black and their alleles within sex Degree of pigmentation and percentages
Sex
Genotype
9 9
No. of birds None
Trace
Distinct
Ii Ii ii ii
Ee ee Ee ee
147 161 191 170
83.0 81.4 45.6 72.9
15.0 13.0 11.0 16.5
2.0 5.6 43.4 10.6
Ii Ii ii ii
Ee ee Ee ee
159 154 143 156
52.8 27.3 32.9 9.6
27.7 14.3 22.4 7.7
19.5 58.4 44.7 82.7
dominant white in combination with extended black greatly reduced the incidence of the character. Its effect on those males carrying restricted black was not so extensive. In females dominant white greatly suppressed the incidence of the character in combination with both extended and restricted black. In Table 4 the data from the still more refined genotypes are presented. In this table the barring and non-barring genotypes are included in addition to those presented in Table 3. The data from only the birds in which classification was definite for barring and non-barring are included.
TABLE 4.—Prevalence and degree of abdominal melanin in relation to combinations of dominant white, extended black, barring and their alleles within sex Degree of pigmentation and percentages Sex
Genotype
No. of birds
Ii Ee Bb Ii Ee bb Iiee Bb Ii ee bb ii Ee Bb ii E e b b ii ee Bb ii ee bb
9 9
Ii Ii Ii Ii ii ii ii ii
Ee BEe bee Bee bEe BEe bee Bee b-
None
Trace
Distinct
62 76 73 44 76 115 80 90
98.4 69.7 74.0 86.4 97.4 11.3 63.7 81.1
1.6 26.3 20.5 6.8 2.6 16.5 21.3 12.2
0.0 4.0 5.5 6.8 0.0 72.2 15.0 6.7
33 88 34 50 84 59 80 75
75.8 39.8 2.9 46.0 56.0 0.0 0.0 20.0
15.1 32.9 2.9 22.0 38.1 0.0 0.0 16.0
9.1 27.3 94.2 32.0 5.9 100.0 100.0 64.0
Downloaded from http://ps.oxfordjournals.org/ at Simon Fraser University on May 29, 2015
is readily apparent that within each sex the over-all effect of dominant white is to greatly reduce the incidence of the character. This is in accord with the findings of Jaap in the papers referred to earlier. However, as will be shown later, dominant white exerts a more intense suppressing effect in combination with certain plumage genes than with others. In Table 3 more refined genotypes are assessed in order to show the effect of dominant white in combination with extended black and with restricted black. Many comparisons could be made from the data presented in Table 3. In males
885
ABDOMINAL BLACK
greater effect on the restricted black, nonbarred genotype. In general the reduction in abdominal melanin deposition due to the presence of dominant white was not as pronounced in the presence of restricted black as in the presence of extended black. As has been stated previously, gold and silver could be assessed with total accuracy in three genotypes of the females. Two of these genotypes, ii Ee b- and ii ee B-, carried distinct abdominal melanin deposition in all individuals. Therefore the classification of silver and gold in combination with these genotypes contributed no information as regards the effect of either gold or silver on the frequency of deposition. However, in these females which carried the ii ee fagenotype this was not the case and the data arising from these birds are presented in Table 5. The data presented in Table 5 indicate that in combination with the ii ee b- genotype the gene for gold promoted the deposition of melanin to a greater extent than did its allele, silver. DISCUSSION
Most of the specific results have already been discussed as the data were presented. In general, however, the data furnish additional evidence to show the pleiotropic effects of certain genes normally associated only with plumage color. Probably the most important aspect of these data and those presented by Jaap is to furnish good evidence in poultry that for certain characters the gene combination or gene complex is as much a factor in the expression
TABLE 5.—Prevalence and degree of abdominal melanin deposition in relation to the presence of silver or gold in the genotype Degree of pigmentation and percentages Sex 9 9 9 9
Genotype ii ee b- Sii ee b- s-
No. of birds 46 29
None
Trace
Distinct
26.1 10.3
17.4 13.8
56.5 75.9
Downloaded from http://ps.oxfordjournals.org/ at Simon Fraser University on May 29, 2015
With the large number of genotypic combinations listed in Table 4 the assessment of the data becomes quite complicated. However, some of the more pertinent observations can be listed. If we start with male birds of the genotype ii Ee bb we find the incidence of abdominal melanin deposition is very high. However, the substitution of either gene I or gene B into this genotype, thus changing it to Ii Ee bb or ii Ee Bb, will greatly reduce the incidence of the character. In these cases it would seem that dominant white and barring had somewhat duplicatory effects since the presence of both genes in the genotype does not greatly enhance the suppression of the character over a genotype which only carries one of the genes. This is particularly true if the single gene combined with extended black is barring. It appears to be a slightly more powerful gene in the presence of extended black than is dominant white. If we start with males and females of the genotypes ii ee bb and ii ee b- respectively, we find a great contrast to the foregoing situation. In combinations with restricted black the addition of the B gene increases rather than decreases the incidence of the character. In the males dominant white reduced the incidence in both the restricted barred and restricted nonbarred genotypes but exerted a more pronounced effect on the restricted black barred genotype. In the females dominant white reduced the incidence of the character in combination with the same genotypes. However, in this sex it exerted
886
C. M. HUNTSMAN, F. N. JEROME AND E. S. SNYDER
of a character as any specific gene itself. This gene complex effect appears to stem from interaction between alleles normally considered to be independent in their effects. The gene interactions described in this paper were further complicated by the fact that sex and gene combinations also interacted as judged by the deposition of abdominal melanin.
REFERENCES Jaap, R. G., 1955. Shank color and barred plumage in columbian-colored chickens. Poultry Sci. 34: 389-395. Jaap, R. G., 1958. Black abdomen—a pleiotropic effect of plumage color genes in broiler chickens. Poultry Sci. 37: 112-116. Huntsman, C. M., F. N. Jerome and E. S. Snyder, 1959. The relationship between plumage color phenotypes and the presence of black melanin in the abdomen of broiler chickens: Study 1. Poultry Sci. 38: 878-881.
The Effect of Pre-incubation Treatments on the Hatchability of Chicken Eggs J. D. MCCONACHIE, F. N. JEROME AND W. F. PEPPER Department of Poultry Husbandry, Ontario Agricultural College, Guelph, Canada (Received for publication October 9, 1959)
R
ECENT publications on the subject of pre-incubation treatments for hatching eggs have indicated that (1) holding eggs at room temperature or (2) heating eggs at incubator temperatures for short periods may be beneficial to hatchability. Hutt and Pilkey (1930) suggest that incubating eggs four to five hours directly after laying could result in the devel-
opment of the embryos beyond the critical stage associated with pre-gastrulation. Hays and Nicolaides (1934) reported that eggs from hens with high hatchability contained more advanced embryos than eggs from low hatching hens, while Taylor and Gunns (193S) reported no correlation between the size of the embryo in the unincubated egg and hatchability. An increase
Downloaded from http://ps.oxfordjournals.org/ at Simon Fraser University on May 29, 2015
SUMMARY 1. The character, black melanin in the abdomen, occurs more frequently in females than in males. 2. Chickens of both sexes of the iEb phenotype carry a high incidence of the character. However, substitution of either dominant white or barring into this phenotype, thus changing it to IEb, or iEB, greatly reduces the incidence of the character. 3. It appears that the I gene and the B gene have duplicatory effects on the incidence of the character since the presence of both genes in an individual does not greatly reduce the incidence of the character over that reduction caused by either gene alone.
4. In chickens which carry the ieb phenotype the males exhibit a low incidence of the character, the females a high incidence. 5. In females which carry the ieb phenotype the sex-linked gene for gold increases the incidence of the character. 6. In addition to demonstrating the pleiotropic effect of a number of plumage color genes, the data show that the expression of the abdominal melanin character depends on the genotypic combination in addition to the specific genes involved. In addition to genotypic interactions, they show that genotype-sex interactions also exist to decrease or increase the incidence of the character.
I
ens in addition to the phenotypes classified in the first study. The major consideration in arranging the matings of the breeding stock was to obtain progeny in which a segregation of eight phenotypes occurred with the same expected frequency within each phenotype. The eight desired phenotypes were: IEB, IEb, IeB, Ieb, iEB, iEb, ieB and ieb. In order to obtain this segregation, a male heterozygous for dominant white and exhibiting black flecks on the body and a ghost barring pattern, was crossed with Columbian Rock females. From the progeny produced, a number of males with a pattern similar to their sire, was selected and mated to unrelated Columbian Rock females to produce the progeny from which the data were gathered. The selection of these particular males gave assurance that the genotypic mating was, Ii Ee Bb $ $ X ii ee b- 9 9 The frequencies occurring in the segregated phenotypes verified the genotypes listed above. In addition, it should be mentioned that the genotype of the paternal grandsire was verified to be Ii Ee Bb Ss. As a result of this genotype a certain frequency of the s gene carried through to the final progeny. Before presenting the data, it may be advisable to describe how the classification for plumage color phenotype was carried out. The iEB and iEb phenotypes are easily recognized at hatching time. Most of the ie phenotypes are distinguished at hatching time by the fact that there are
882
Downloaded from http://ps.oxfordjournals.org/ at Simon Fraser University on May 29, 2015
N THEIR original study (Huntsman, Jerome and Snyder, 1959) the authors reported on the relationship of four color phenotypes to the deposition of black melanin in the abdomen of broiler chickens. The four phenotypes classified were, extended black, barred (EB); extended black, non-barred (Eb); restricted black, barred (eB); and restricted black, nonbarred (eb). It was found that the combination of extended black and barring tended to decrease the incidence of melanin deposition in the abdomen below the average for all phenotypes. In contrast to this, the combination of restricted black and barring tended to increase the frequency of this deposition above the average for all phenotypes. The deposition of melanin was found to occur more than twice as frequently in females as in males. These results substantiated those reported by Jaap (1955) and again by Jaap (1958). The data presented by Huntsman et al. showed that in some comparisons extreme interactions occurred between sex and genotype as measured by the incidence of deposition of melanin. For example, when the phenotype was restricted black there was a great variation in frequency between the sexes. When the phenotype was extended black the variation between the sexes was greatly reduced. The study to be reported here was carried out in order to investigate the effect of dominant white on the deposition of melanin in the abdomen of broiler chick-
m
ABDOMINAL BLACK
TABLE 1.—Prevalence and degree of abdominal melanin deposition in relation to sex
Sex
9 9
No. of birds 669 612
Degree of pigmentation and percentages None
Trace
Distinct
69.4 30.7
13.7 18.0
16.9 51.3
of gold or silver could be assessed accurately only in certain combinations. These combinations occurred only in the female progeny and were genotypically ii ee b-, ii ee B- or ii Ee b-. In the last mentioned genotype the females carrying gold had gold lacing on the neck, those carrying silver had silver lacing on the neck. A total progeny of 1281 individuals, produced from four weekly hatches, were reared to approximately 11 weeks of age, at which time they were killed and examined for the presence and degree of melanin deposition. In Table 1, data are presented to show the relative incidence of the character within the sexes. The data presented above agree well with those from former work and add further evidence to show that females carry a higher frequency of abdominal melanin deposition. One of the main objectives of this study was to observe the effect of dominant white on the incidence of this character. The data pertinent to this phase of the study are presented in Table 2. From the data presented in Table 2 it
TABLE 2.—Prevalence and degree of abdominal melanin deposition in relation to dominant white and its allele within sex Degree of pigmentation and percentages Sex
Genotype
1
d'c?
Ii ii
9 9
Ii ii
No . of birds None
Trace
Disl inct
308 361
82.1 58.4
14.0 13.6
3.9 28.0
313 299
40.2 20.7
21.1 14.7
38.7 64.6
Downloaded from http://ps.oxfordjournals.org/ at Simon Fraser University on May 29, 2015
no black flecks on the body but black pigment is present in the primary wing quills. Any mistakes originating through the nonappearance of black in the quills can be corrected when the birds grow tail and wing feathers. Barring and non-barring can also be recognized at this time in these particular birds. The IE and Ie phenotypes can be distinguished at hatching time by the fact that although both types lack black pigment in the primary wing quills, the IE phenotype will almost invariably exhibit at least a few strands of black down somewhere on the body while the Ie phenotype will not. The chief difficulty encountered was in the classification of barring and non-barring in the presence of dominant white. Certain individuals carried almost pure white plumage and could not be classified for the presence or absence of barring. However, many of the dominant white phenotypes exhibited a creamish or brownish shade of color at 9 weeks of age and it served as a suitable background for the barred and non-barred characters. In the IE phenotypes there were sufficient black areas on the feathers of certain individuals, to denote whether barring was present or absent. All classifications involving barring and non-barring in the presence of dominant white were carried out independently by two of the authors. The few birds on which there was disagreement or doubt were classed as unidentified. The presence
884
C. M. HUNTSMAN, F. N. JEROME AND E. S. SNYDER TABLE 3.-
-Prevalence and degree of dominant white and
melanin deposition in relation to combinations of black and their alleles within sex Degree of pigmentation and percentages
Sex
Genotype
9 9
No. of birds None
Trace
Distinct
Ii Ii ii ii
Ee ee Ee ee
147 161 191 170
83.0 81.4 45.6 72.9
15.0 13.0 11.0 16.5
2.0 5.6 43.4 10.6
Ii Ii ii ii
Ee ee Ee ee
159 154 143 156
52.8 27.3 32.9 9.6
27.7 14.3 22.4 7.7
19.5 58.4 44.7 82.7
dominant white in combination with extended black greatly reduced the incidence of the character. Its effect on those males carrying restricted black was not so extensive. In females dominant white greatly suppressed the incidence of the character in combination with both extended and restricted black. In Table 4 the data from the still more refined genotypes are presented. In this table the barring and non-barring genotypes are included in addition to those presented in Table 3. The data from only the birds in which classification was definite for barring and non-barring are included.
TABLE 4.—Prevalence and degree of abdominal melanin in relation to combinations of dominant white, extended black, barring and their alleles within sex Degree of pigmentation and percentages Sex
Genotype
No. of birds
Ii Ee Bb Ii Ee bb Iiee Bb Ii ee bb ii Ee Bb ii E e b b ii ee Bb ii ee bb
9 9
Ii Ii Ii Ii ii ii ii ii
Ee BEe bee Bee bEe BEe bee Bee b-
None
Trace
Distinct
62 76 73 44 76 115 80 90
98.4 69.7 74.0 86.4 97.4 11.3 63.7 81.1
1.6 26.3 20.5 6.8 2.6 16.5 21.3 12.2
0.0 4.0 5.5 6.8 0.0 72.2 15.0 6.7
33 88 34 50 84 59 80 75
75.8 39.8 2.9 46.0 56.0 0.0 0.0 20.0
15.1 32.9 2.9 22.0 38.1 0.0 0.0 16.0
9.1 27.3 94.2 32.0 5.9 100.0 100.0 64.0
Downloaded from http://ps.oxfordjournals.org/ at Simon Fraser University on May 29, 2015
is readily apparent that within each sex the over-all effect of dominant white is to greatly reduce the incidence of the character. This is in accord with the findings of Jaap in the papers referred to earlier. However, as will be shown later, dominant white exerts a more intense suppressing effect in combination with certain plumage genes than with others. In Table 3 more refined genotypes are assessed in order to show the effect of dominant white in combination with extended black and with restricted black. Many comparisons could be made from the data presented in Table 3. In males
885
ABDOMINAL BLACK
greater effect on the restricted black, nonbarred genotype. In general the reduction in abdominal melanin deposition due to the presence of dominant white was not as pronounced in the presence of restricted black as in the presence of extended black. As has been stated previously, gold and silver could be assessed with total accuracy in three genotypes of the females. Two of these genotypes, ii Ee b- and ii ee B-, carried distinct abdominal melanin deposition in all individuals. Therefore the classification of silver and gold in combination with these genotypes contributed no information as regards the effect of either gold or silver on the frequency of deposition. However, in these females which carried the ii ee fagenotype this was not the case and the data arising from these birds are presented in Table 5. The data presented in Table 5 indicate that in combination with the ii ee b- genotype the gene for gold promoted the deposition of melanin to a greater extent than did its allele, silver. DISCUSSION
Most of the specific results have already been discussed as the data were presented. In general, however, the data furnish additional evidence to show the pleiotropic effects of certain genes normally associated only with plumage color. Probably the most important aspect of these data and those presented by Jaap is to furnish good evidence in poultry that for certain characters the gene combination or gene complex is as much a factor in the expression
TABLE 5.—Prevalence and degree of abdominal melanin deposition in relation to the presence of silver or gold in the genotype Degree of pigmentation and percentages Sex 9 9 9 9
Genotype ii ee b- Sii ee b- s-
No. of birds 46 29
None
Trace
Distinct
26.1 10.3
17.4 13.8
56.5 75.9
Downloaded from http://ps.oxfordjournals.org/ at Simon Fraser University on May 29, 2015
With the large number of genotypic combinations listed in Table 4 the assessment of the data becomes quite complicated. However, some of the more pertinent observations can be listed. If we start with male birds of the genotype ii Ee bb we find the incidence of abdominal melanin deposition is very high. However, the substitution of either gene I or gene B into this genotype, thus changing it to Ii Ee bb or ii Ee Bb, will greatly reduce the incidence of the character. In these cases it would seem that dominant white and barring had somewhat duplicatory effects since the presence of both genes in the genotype does not greatly enhance the suppression of the character over a genotype which only carries one of the genes. This is particularly true if the single gene combined with extended black is barring. It appears to be a slightly more powerful gene in the presence of extended black than is dominant white. If we start with males and females of the genotypes ii ee bb and ii ee b- respectively, we find a great contrast to the foregoing situation. In combinations with restricted black the addition of the B gene increases rather than decreases the incidence of the character. In the males dominant white reduced the incidence in both the restricted barred and restricted nonbarred genotypes but exerted a more pronounced effect on the restricted black barred genotype. In the females dominant white reduced the incidence of the character in combination with the same genotypes. However, in this sex it exerted
886
C. M. HUNTSMAN, F. N. JEROME AND E. S. SNYDER
of a character as any specific gene itself. This gene complex effect appears to stem from interaction between alleles normally considered to be independent in their effects. The gene interactions described in this paper were further complicated by the fact that sex and gene combinations also interacted as judged by the deposition of abdominal melanin.
REFERENCES Jaap, R. G., 1955. Shank color and barred plumage in columbian-colored chickens. Poultry Sci. 34: 389-395. Jaap, R. G., 1958. Black abdomen—a pleiotropic effect of plumage color genes in broiler chickens. Poultry Sci. 37: 112-116. Huntsman, C. M., F. N. Jerome and E. S. Snyder, 1959. The relationship between plumage color phenotypes and the presence of black melanin in the abdomen of broiler chickens: Study 1. Poultry Sci. 38: 878-881.
The Effect of Pre-incubation Treatments on the Hatchability of Chicken Eggs J. D. MCCONACHIE, F. N. JEROME AND W. F. PEPPER Department of Poultry Husbandry, Ontario Agricultural College, Guelph, Canada (Received for publication October 9, 1959)
R
ECENT publications on the subject of pre-incubation treatments for hatching eggs have indicated that (1) holding eggs at room temperature or (2) heating eggs at incubator temperatures for short periods may be beneficial to hatchability. Hutt and Pilkey (1930) suggest that incubating eggs four to five hours directly after laying could result in the devel-
opment of the embryos beyond the critical stage associated with pre-gastrulation. Hays and Nicolaides (1934) reported that eggs from hens with high hatchability contained more advanced embryos than eggs from low hatching hens, while Taylor and Gunns (193S) reported no correlation between the size of the embryo in the unincubated egg and hatchability. An increase
Downloaded from http://ps.oxfordjournals.org/ at Simon Fraser University on May 29, 2015
SUMMARY 1. The character, black melanin in the abdomen, occurs more frequently in females than in males. 2. Chickens of both sexes of the iEb phenotype carry a high incidence of the character. However, substitution of either dominant white or barring into this phenotype, thus changing it to IEb, or iEB, greatly reduces the incidence of the character. 3. It appears that the I gene and the B gene have duplicatory effects on the incidence of the character since the presence of both genes in an individual does not greatly reduce the incidence of the character over that reduction caused by either gene alone.
4. In chickens which carry the ieb phenotype the males exhibit a low incidence of the character, the females a high incidence. 5. In females which carry the ieb phenotype the sex-linked gene for gold increases the incidence of the character. 6. In addition to demonstrating the pleiotropic effect of a number of plumage color genes, the data show that the expression of the abdominal melanin character depends on the genotypic combination in addition to the specific genes involved. In addition to genotypic interactions, they show that genotype-sex interactions also exist to decrease or increase the incidence of the character.