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Association of Dominant Marker Traits and Metric Traits in Chickens
Association of Dominant Marker Traits and Metric Traits in Chickens R. N. SHOFFNER and J. S. OTIS Department of Animal Science, University of Minnesota, St. Paul, Minnesota 55108 V. A. GARWOOD
ABSTRACT This study was initiated to determine whether an allelic substitution of a dominant marker gene would identify a region close to a locus affecting expression in a metric trait. The rationale for the experiment was to utilize disequilibrium between a multiple recessive randombred Rhode Island Red (RRc) stock previously selected for quantitative trait performance and an unimproved dominant marker stock (MDM). The reporter genes in the MDM were: barring (B), silver (S), creeper (Cp), rose comb (R), double uropygial gland (U), crest (Cr), dominant white (I), frizzle (F), duplex comb (D), multiple spurs (M), Polydactyly (Po), blue egg (O), pea comb (P), naked neck (Na), extended black (£), white skin (W+), muffs and beard (Mb), and feathered shanks (Fsh). Appropriate reciprocal crosses of MDM with RRc and Fa to RRc produced segregating full sibs that were evaluated for association with reporter traits. Carriers of Cr, I, and F were significantly later in sexual maturity than their recessive full sibs. The pleiotropic effects of F are believed to account for the later maturity. None of the marker traits had a significant association with egg numbers or egg weight. Birds expressing £ were distinctly heavier at 8 and 32 wk. There is no obvious explanation for the significant larger size for the E phenotype. The CR-I-F phenotypes were significantly smaller at 32 wk than noncarrier full sibs. (Key words: linkage, pleiotropy, reporter genes, metric traits, sexual maturity) 1993 Poultry Science 72:1405-1410
Merat (1990). A trait used as a marker may have a pleiotropic effect on a metric trait Poultry breeders have speculated about conferring either a reduced or elevated the existence of reporter genes or blocks of expression. Gene to gene interaction or genes that may have a measurable associa- gene-environmental interactions may also tion with expression in economic traits. influence the degree of apparent associaThis study was initiated to determine tion between a marker trait and metric whether an allelic substitution of a domi- expression. nant marker gene would identify a region The linkage covariance of a metric trait close to a locus or loci affecting expression with a marker locus is related to the in a metric trait. Clearcut differentiation proximity of the marker locus to genes between pleiotropic and linkage effects is that affect the metric trait and the amount not distinguished easily, as discussed by of genetic variation in the metric trait. Correlation between marker loci and metric trait genes depends upon intrachromosomal distribution. Estimates for Received for publication September 28, 1992. association can be derived from crossing a Accepted for publication March 26, 1993. INTRODUCTION
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Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on May 24, 2015
USDA, Agricultural Research Service, Poultry Research Laboratory, Georgetown, Delaware 19947
1406
SHOFFNER ET AL.
The Minnesota dominant marker (MDM) stock is a synthetic population with 20 dominant single locus traits secured from exotic stocks with no history of intensive selection for metric traits. Breed and varieties included were: Egyptian Fayoumi, Japanese Bantam, Blue Andalusian, Crested Polish, White Leghorn, Barred Plymouth Rocks, and other miscellaneous stocks carrying desired dominant traits. Eight generations of selection were directed toward attaining a gene frequency of .5 for each trait in all individuals. The creeper (Cp) trait was an exception, as it was introduced in the last two generations prior to homozygous line formation. Because of its lethality in homozygotes and some deliberate limitation, the frequency was about .05 in the pure line and less than .0125 in the backcross. Nine lines were established from this heterozygous population, each homozygous for presumed linkage groups and single gene traits (Hutt, 1949; Somes, 1988). The inheritance and original investigator references are given by Hutt (1949). Line BS included the sex chromosome loci barring (B) and silver (S); Line Cp-R-U was composed of creeper {Cp), rose comb (R), and double uropygial gland (U); Line Cr-I-F included crest (O), dominant white (I), and
Experimental Design The rationale for the experiment was to utilize disequilibrium between the RRc stock selected for quantitative trait performance and the unimproved MDM stock. Reciprocal matings with 32 males and 64 females were made between RRc and MDM lines, thereby minimizing sex-linked and maternal effects in the Fx progeny. Matings were made in small trapnest-equipped floor pens. The Fa progeny were maintained at the University of Minnesota. The Fj males and females were selected for backcrossing to recessive RRc to produce segregating backcross progeny. Reciprocal backcross matings involving 64 males and 128 females (Table 1) were made in trapnest pens. Eggs were pedigreed and saved for two hatches (each with a 14-day collection period) and shipped to the USDA Regional Laboratory at Purdue University. Hatching, rearing, descriptive sorting, and layer housing were carried out at this location. Males were excluded from the experiment at hatching time for economic reasons, assuming that female body weights would provide adequate information for discrimination. Females were brooded in floor pens to 8 wk and transferred to growing sheds until 20 wk.
Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on May 24, 2015
stock selected for one or more metric traits frizzle (F); Line D-M-Po had duplex comb to an unselected marker trait line, making (D), multiple spurs (M), and Polydactyly the appropriate backcrosses, and observ- (Po); Line O-P-Na consisted of blue egg (O), ing segregation progenies. The feasibility pea comb (P), and naked neck (Na); Line E, of this scheme was demonstrated by extended black (E); Line W, white skin (W+); Thoday (1961) in Drosophila melanogaster.Line Mb, muffs and beard (Mb); and Line There is considerable literature on the Fsh, feathered shanks (Fsh). Periodic inchicken concerning association between troductions of homozygotes from the MDM marker traits, recognizable by phenotype, segregating population were made into and expression of metric traits. These have each line to minimize inbreeding and been largely summarized by Hutt (1949), genetic drift. Smyth (1969, 1990), and Merat (1990). The A multiple recessive population of majority of associations indicate Rhode Island Reds (RRc) was developed as pleiotropic effects rather than linkage. This a random breeding control by combining study attempted to determine whether four intensively selected commercial Rhode any genes for metric traits in the chicken Island Red egg production strains at the could be linked or associated with major USDA North Central Regional Poultry linkage groups or with traits not assigned Breeding Laboratory, formerly located at to a linkage group. Purdue University, West Lafayette, IN 47907 (Kinney and Lowe, 1968). This population was in the sixth generation of relaxed MATERIALS AND METHODS selection at the beginning of the experiment. Genetic Stocks
ASSOCIATION OF PHENOTYPIC AND METRIC TRAITS IN CHICKENS
1407
TABLE 1. Sets with one male and two females used in backcross matings to produce segregating progeny1 Mating group
Male parent
Female parent
I ffl H IV
16 16 16 16
32 32 32 32
(MDM
RRc (MDM 3 x RRc 9 9) RRc (RRc <$ x MDM 9 9)
] MDM = the Minnesota Dominant Marker population; RRc = the randombred Rhode Island Red control population.
and 32-wk body weights were recorded in grams. Statistical Analysis
The analysis of variance linear model (SAS Institute, 1982) was used to discriminate between segregates. The model included the following variables: Pyk = n + Yj + Rj + H k + m + YHjk + RHjk + YRHijk + si + ejjki, where P = phenotype; the fixed Identification of Segregating variables are Y = year, H = hatches, and the Full Sibs interactions YR, YH, RH, and YRH; s = segregates, a random variable; and e = At 20 wk of age phenotypic descriptions error. Least squares means and SE for each were taken on females for classification as trait were extracted for full-sib comparieither marker (M) or recessive (m). At least sons. one and wherever possible two full sibs of each segregating phenotype were ranRESULTS AND DISCUSSION domly placed in individual cages for performance records. Expression of all marker The effects of allelic substitution were traits except for W+ was modified some- estimated by comparing the level of exwhat in the heterozygotes but was readily pression of metric traits in sets of segregatclassifiable. Those with M traits carried a ing full sibs. Differences occurred between portion of chromosome around the locus as line backcrosses for almost all traits, well as other nonrecombinant portions of reflecting in part the genetic background the M trait chromosome. When sorted for of parent lines and chance differences in VV+, E, Mb, and Fsh there were only M and m founder parents. There were also differfull sibs. In the case of linked genes such as ences between years and other variables, Cr-I-F, those individuals carrying Cr-I-F, as might be expected from data collected Cr-F, Cr, I, and F were classified as M. The over a 4-yr replication period. The results same procedure was followed for other are given in Table 2. All traits except W+ incomplete dominance, resulting in presumed linked loci, including Cp-R-U, D- have attenuated expression in the backcross M-Po, and O-P-Na. heterozygote (Mm). This expression may very well extend to altered pleiotropic effects on metric traits. If only linkage is Metric Traits Measured involved, the heterozygous marker gene Age at first egg was recorded in weeks identifies associated loci affecting the metfrom date of hatching to date first egg was ric trait. laid. Egg production was measured as number of eggs laid per hen housed until 496 days of age. Egg weight in grams was Age at First Egg taken from an average of 10 eggs collected Carriers of Cr, I, and F were significantly from each hen starting at 32 wk of age. Eight later in sexual maturity than their recessive
Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on May 24, 2015
Dietary requirements (NRC, 1984) for starting, growing, and laying periods were formulated at each location. Both feed and water were available for ad libitum consumption. The only light control was the institution of continuous 14 h light/10 h dark 1 wk after housing (21 wk of age). The mating scheme and sibling comparisons were followed for 4 consecutive yr.
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SHOFFNER ET AL.
TABLE 2. Comparison of least squares means ± SE of quantitative traits between sibs segregating for the dominant marker1 Age at first egg
Line B-S Cp-R-U Cr-I-F D-M-Po
E W Mb Fsh
(wk) 24.1 ± .30 24.1 ± .20 25.4 ± .20 25.0 ± .20 24.3 ± .17** 23.6 ± .18 24.3 ± .22 24.9 ± .24 23.8 ± .21 24.5 ± .22 24.5 ± .10 24.6 ± .10 23.6 ± .16 23.8 ± ,10 25.3 ± .20 24.8 ± .20 25.6 ± .20 25.3 ± .20
(no.) 173 ± 4 173 ± 3 158 ± 3 169 ± 3 164 ± 3 168 ± 3 172 ± 3 168 ± 3 161 ± 3 167 ± 3 162 ± 3 159 ± 3 172 ± 3 171 ± 3 168 ± 3 167 ± 3 160 ± 3 165 ± 3
Egg weight
Body weight 8 wk
32 wk
/~\ 50 50 49 49 50 50 51 51 51 51 50 50 50 50 51 51 52 51
± .4 ± .4 ± .3 ± .3 ± .3 ± .3 ±.3 ± .3 ± .3 ± .3 ± .2 ± .2 ± .2 ± .2 ± .3 ± .3 ± .3 ± .3
y&
702 ± 9 703 ± 8 634 ± 6 645 ± 6 681 ± 5 700 ± 6 711 ± 6 700 ± 7 702 ± 7 699 ± 7 712 ± 6*** 679 ± 6 668 ± 5 675 ± 5 706 ± 5 700 ± 5 710 ± 6 710 ±7
2,233 ± 29 2,225 ± 24 2,188 ± 19 2,210 ± 19 2,243 ± 18** 2,318 ± 19 2,275 ± 21 2,245 ± 23 2,191 ± 23 2,267 ± 23 2,301 ± 19** 2,250 ± 19 2,134 ± 17 2,145 ± 17 2,312 ± 20 2,290 ± 19 2,301 ± 21 2,295 ± 21
1
The number of full-sib comparisons for each phenotypic class ranged from 304 to 613 for age at first egg, 304 to 613 for egg production, 303 to 537 for egg weight, 312 to 629 for 8-wk weight, and 306 to 614 for 32-wk weight. The total number of observations varied between 3,928 and 4,511. 2 M indicates marker, m indicates nonmarker progeny. "Comparison of marker with nonmarker progeny (P > .01). •"Comparison of marker with nonmarker progeny (P > .001).
full sibs (Table 2). Gene F is suspected as would require very tight linkage of a having the major influence, as neither Cr marker trait with major loci or alternatively nor I phenotypes have been found to have pleiotropic effects. later onset of lay. The defective feather structure alters insulating capability so Egg Weight at Thirty-Two birds are more susceptible to fluctuating Weeks of Age ambient temperatures. Hutt (1949) reported There were no differences between fulllater sexual maturity for frizzled birds. Under tropical conditions with higher am- sib segregates for egg size at 32 wk of age bient temperatures, F may be beneficial (Table 2). (Horst, 1987). Eight-Week Weight Egg Production to Fifty Weeks of Age
Birds expressing £ were distinctly heavier at 8 wk of age compared with non-E full sibs (Table 2). Comparisons cited by Smyth None of the marker traits showed a (1969) indicate variable expression for body significant association with egg numbers, size of E carriers. The RRc parent line although there was a difference of 11 eggs ranged from 50 to 100 g heavier than the E in favor of recessive full sibs versus Cp-R-U parent line at 8 wk of age. In view of this carriers that approached the 5% level of parental difference and the mating system significance (Table 2). Considering the low used to produce segregates, no contribution heritability of egg production, association from RRc additive genetic source is evident.
Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on May 24, 2015
O-P-Na
M* m M m M m M m M m M m M m M m M m
Egg production
ASSOCIATION OF PHENOTYPIC AND METRIC TRAITS IN CHICKENS
Adult Body Weight at Thirty-Two Weeks of Age
ing hypervariable DNA regions such as microsatellite polymorphisms that are nonexpressing and promise to be efficient markers for identifying regions associated with variable expression in metric traits. ACKNOWLEDGMENTS
The authors express appreciation to Phillip Lowe, Bernard Wienland, James Bitgood, and Robert Smyth for their assistance and advice. This study was made in cooperation with the North Central Regional Poultry Breeding Project 168 and is a publication of the Minnesota Agricultural Experiment Station, Scientific Journal Series Article Number 20072. REFERENCES Carefoot, W. C, 1990. Test for linkage between the eumelanin dilution blue (B/), the extended black (E) allele at the E locus and the linked pea comb (P) and eumelanin extension (Ml) genes in the domestic fowl. Br. Poult. Sci. 31:465-472. Horst, P., 1987. Animal genetic resources and potential resource development in the tropics with special references to Malaysia. Malays. Appl. Biol. 16:13-22. Horst, P., and H. W. Rauen, 1986. Significance of the naked neck gene (Na-gene) in poultry breeding in the tropics. Pages 191-195 in: Proceedings of the 7th European Poultry Conference, Vol. 1, Paris, France. Hurt, F. B., 1949. Genetics of the Fowl. McGraw-Hill Book Co. Inc., New York, NY. Kinney, T. B., Jr., and P. C. Lowe, 1968. Genetic and phenotypic variation in the Regional Red Control over nine years. Poultry Sci. 47:1105-1110. Merat, P., 1990. Pleiotropic and associated effects of major genes. Ch. 20. Pages 429-467 in: Poultry Breeding and Genetics. R. D. Crawford, ed. Elsevier, Amsterdam, The Netherlands. National Research Council, 1984. Nutrient Requirements of Poultry. 8th rev. ed. National Academy Press, Washington, DC SAS Institute, 1982. SAS® User's Guide: Statistics. 1982 ed. SAS Institute Inc., Cary, NC. Shaw, E. M., R. N. Shoffner, D. N. Foster, and K. S. Guise, 1991. Mapping of the growth hormone gene by in situ hybridization to chromosome 1. J. Hered. 82:505-508. Smyth, J. R., Jr., 1969. Relationship between genes affecting melanin pigmentation and other traits in the fowl. World's Poult. Sci. J. 25:6-14. Smyth, J. R., Jr., 1990. Genetics of plumage, skin and eye pigmentation in chickens. Ch. 5. Pages 109-167 in: Poultry Breeding and Genetics. R. D. Crawford, ed. Elsevier, Amsterdam, The Netherlands. Smyth, J. R., Jr., and F. A. Ponce de Leon, 1992.
Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on May 24, 2015
The E genotype was significantly heavier at adult size than non-E segregates (Table 2). On the basis of size differential at 8 wk of age, this advantage could be extended to adult body size for the E genotype. The Cr-I-F phenotypes were significantly smaller at 32 wk of age, compared with their full-sib segregates. This was not unexpected, as both I and F carriers have been found to be at a weight disadvantage in numerous comparisons (Smyth, 1969, 1990; M6rat, 1990). The Cr-I-F chicks were 19 g lighter than segregating sibs at 8 wk of age. Although this was not a significant difference at this age, it was predictive of body size difference at adult age. The fact that pleiotropic effects were expressed as expected gives credence to the validity of the design for discrimination between E and non-E phenotypes. The traits J and F were associated with pleiotropic effects as previously reported. Trait No. did not have pronounced pleiotropic effects (Horst and Rauen, 1986), evidently because of moderate temperatures as well as considerable recovery of body feathering in the backcross. The homozygous Na line had greatly reduced feathering in the pterylae and apteria body area and greatly reduced hatchability. The frequency of Cp was so low that it had little impact on variable expression for the Cp-R-U linkage group. The linkage or positive pleiotropic effect of E appears to be real and merits further exploration. Recently, Carefoot (1990) and Smyth and Ponce de Leon (1992) provided evidence that the locus for E was linked to P on Chromosome 1. Pea comb is located on the p arm and the growth hormone (GH) gene is located approximately in the G band region lg4 on the opposite arm (Shaw et al, 1991). Whether the E and GH loci are sufficiently close together for the apparent effects of E on growth to result from the GH locus is unknown, but because of chromosomal distance and high recombination rate it does not seem likely. Genetic modifications of morphological traits are generally not very efficient markers, especially when there are few. There are now available techniques for recogniz-
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Research note: Linkage between the pea comb (P) and extended black loci of the chicken. Poultry Sci. 71:208-210. Somes, R. G., Jr., 1988. International Registry of
Poultry Genetic Stocks. Storrs Agricultural Experiment Station Bulletin 476, Storrs, CT. Thoday, J. M., 1961. Location of polygenes. Nature 191:368-370.
Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on May 24, 2015
ABSTRACT This study was initiated to determine whether an allelic substitution of a dominant marker gene would identify a region close to a locus affecting expression in a metric trait. The rationale for the experiment was to utilize disequilibrium between a multiple recessive randombred Rhode Island Red (RRc) stock previously selected for quantitative trait performance and an unimproved dominant marker stock (MDM). The reporter genes in the MDM were: barring (B), silver (S), creeper (Cp), rose comb (R), double uropygial gland (U), crest (Cr), dominant white (I), frizzle (F), duplex comb (D), multiple spurs (M), Polydactyly (Po), blue egg (O), pea comb (P), naked neck (Na), extended black (£), white skin (W+), muffs and beard (Mb), and feathered shanks (Fsh). Appropriate reciprocal crosses of MDM with RRc and Fa to RRc produced segregating full sibs that were evaluated for association with reporter traits. Carriers of Cr, I, and F were significantly later in sexual maturity than their recessive full sibs. The pleiotropic effects of F are believed to account for the later maturity. None of the marker traits had a significant association with egg numbers or egg weight. Birds expressing £ were distinctly heavier at 8 and 32 wk. There is no obvious explanation for the significant larger size for the E phenotype. The CR-I-F phenotypes were significantly smaller at 32 wk than noncarrier full sibs. (Key words: linkage, pleiotropy, reporter genes, metric traits, sexual maturity) 1993 Poultry Science 72:1405-1410
Merat (1990). A trait used as a marker may have a pleiotropic effect on a metric trait Poultry breeders have speculated about conferring either a reduced or elevated the existence of reporter genes or blocks of expression. Gene to gene interaction or genes that may have a measurable associa- gene-environmental interactions may also tion with expression in economic traits. influence the degree of apparent associaThis study was initiated to determine tion between a marker trait and metric whether an allelic substitution of a domi- expression. nant marker gene would identify a region The linkage covariance of a metric trait close to a locus or loci affecting expression with a marker locus is related to the in a metric trait. Clearcut differentiation proximity of the marker locus to genes between pleiotropic and linkage effects is that affect the metric trait and the amount not distinguished easily, as discussed by of genetic variation in the metric trait. Correlation between marker loci and metric trait genes depends upon intrachromosomal distribution. Estimates for Received for publication September 28, 1992. association can be derived from crossing a Accepted for publication March 26, 1993. INTRODUCTION
1405
Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on May 24, 2015
USDA, Agricultural Research Service, Poultry Research Laboratory, Georgetown, Delaware 19947
1406
SHOFFNER ET AL.
The Minnesota dominant marker (MDM) stock is a synthetic population with 20 dominant single locus traits secured from exotic stocks with no history of intensive selection for metric traits. Breed and varieties included were: Egyptian Fayoumi, Japanese Bantam, Blue Andalusian, Crested Polish, White Leghorn, Barred Plymouth Rocks, and other miscellaneous stocks carrying desired dominant traits. Eight generations of selection were directed toward attaining a gene frequency of .5 for each trait in all individuals. The creeper (Cp) trait was an exception, as it was introduced in the last two generations prior to homozygous line formation. Because of its lethality in homozygotes and some deliberate limitation, the frequency was about .05 in the pure line and less than .0125 in the backcross. Nine lines were established from this heterozygous population, each homozygous for presumed linkage groups and single gene traits (Hutt, 1949; Somes, 1988). The inheritance and original investigator references are given by Hutt (1949). Line BS included the sex chromosome loci barring (B) and silver (S); Line Cp-R-U was composed of creeper {Cp), rose comb (R), and double uropygial gland (U); Line Cr-I-F included crest (O), dominant white (I), and
Experimental Design The rationale for the experiment was to utilize disequilibrium between the RRc stock selected for quantitative trait performance and the unimproved MDM stock. Reciprocal matings with 32 males and 64 females were made between RRc and MDM lines, thereby minimizing sex-linked and maternal effects in the Fx progeny. Matings were made in small trapnest-equipped floor pens. The Fa progeny were maintained at the University of Minnesota. The Fj males and females were selected for backcrossing to recessive RRc to produce segregating backcross progeny. Reciprocal backcross matings involving 64 males and 128 females (Table 1) were made in trapnest pens. Eggs were pedigreed and saved for two hatches (each with a 14-day collection period) and shipped to the USDA Regional Laboratory at Purdue University. Hatching, rearing, descriptive sorting, and layer housing were carried out at this location. Males were excluded from the experiment at hatching time for economic reasons, assuming that female body weights would provide adequate information for discrimination. Females were brooded in floor pens to 8 wk and transferred to growing sheds until 20 wk.
Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on May 24, 2015
stock selected for one or more metric traits frizzle (F); Line D-M-Po had duplex comb to an unselected marker trait line, making (D), multiple spurs (M), and Polydactyly the appropriate backcrosses, and observ- (Po); Line O-P-Na consisted of blue egg (O), ing segregation progenies. The feasibility pea comb (P), and naked neck (Na); Line E, of this scheme was demonstrated by extended black (E); Line W, white skin (W+); Thoday (1961) in Drosophila melanogaster.Line Mb, muffs and beard (Mb); and Line There is considerable literature on the Fsh, feathered shanks (Fsh). Periodic inchicken concerning association between troductions of homozygotes from the MDM marker traits, recognizable by phenotype, segregating population were made into and expression of metric traits. These have each line to minimize inbreeding and been largely summarized by Hutt (1949), genetic drift. Smyth (1969, 1990), and Merat (1990). The A multiple recessive population of majority of associations indicate Rhode Island Reds (RRc) was developed as pleiotropic effects rather than linkage. This a random breeding control by combining study attempted to determine whether four intensively selected commercial Rhode any genes for metric traits in the chicken Island Red egg production strains at the could be linked or associated with major USDA North Central Regional Poultry linkage groups or with traits not assigned Breeding Laboratory, formerly located at to a linkage group. Purdue University, West Lafayette, IN 47907 (Kinney and Lowe, 1968). This population was in the sixth generation of relaxed MATERIALS AND METHODS selection at the beginning of the experiment. Genetic Stocks
ASSOCIATION OF PHENOTYPIC AND METRIC TRAITS IN CHICKENS
1407
TABLE 1. Sets with one male and two females used in backcross matings to produce segregating progeny1 Mating group
Male parent
Female parent
I ffl H IV
16 16 16 16
32 32 32 32
(MDM
RRc (MDM 3 x RRc 9 9) RRc (RRc <$ x MDM 9 9)
] MDM = the Minnesota Dominant Marker population; RRc = the randombred Rhode Island Red control population.
and 32-wk body weights were recorded in grams. Statistical Analysis
The analysis of variance linear model (SAS Institute, 1982) was used to discriminate between segregates. The model included the following variables: Pyk = n + Yj + Rj + H k + m + YHjk + RHjk + YRHijk + si + ejjki, where P = phenotype; the fixed Identification of Segregating variables are Y = year, H = hatches, and the Full Sibs interactions YR, YH, RH, and YRH; s = segregates, a random variable; and e = At 20 wk of age phenotypic descriptions error. Least squares means and SE for each were taken on females for classification as trait were extracted for full-sib comparieither marker (M) or recessive (m). At least sons. one and wherever possible two full sibs of each segregating phenotype were ranRESULTS AND DISCUSSION domly placed in individual cages for performance records. Expression of all marker The effects of allelic substitution were traits except for W+ was modified some- estimated by comparing the level of exwhat in the heterozygotes but was readily pression of metric traits in sets of segregatclassifiable. Those with M traits carried a ing full sibs. Differences occurred between portion of chromosome around the locus as line backcrosses for almost all traits, well as other nonrecombinant portions of reflecting in part the genetic background the M trait chromosome. When sorted for of parent lines and chance differences in VV+, E, Mb, and Fsh there were only M and m founder parents. There were also differfull sibs. In the case of linked genes such as ences between years and other variables, Cr-I-F, those individuals carrying Cr-I-F, as might be expected from data collected Cr-F, Cr, I, and F were classified as M. The over a 4-yr replication period. The results same procedure was followed for other are given in Table 2. All traits except W+ incomplete dominance, resulting in presumed linked loci, including Cp-R-U, D- have attenuated expression in the backcross M-Po, and O-P-Na. heterozygote (Mm). This expression may very well extend to altered pleiotropic effects on metric traits. If only linkage is Metric Traits Measured involved, the heterozygous marker gene Age at first egg was recorded in weeks identifies associated loci affecting the metfrom date of hatching to date first egg was ric trait. laid. Egg production was measured as number of eggs laid per hen housed until 496 days of age. Egg weight in grams was Age at First Egg taken from an average of 10 eggs collected Carriers of Cr, I, and F were significantly from each hen starting at 32 wk of age. Eight later in sexual maturity than their recessive
Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on May 24, 2015
Dietary requirements (NRC, 1984) for starting, growing, and laying periods were formulated at each location. Both feed and water were available for ad libitum consumption. The only light control was the institution of continuous 14 h light/10 h dark 1 wk after housing (21 wk of age). The mating scheme and sibling comparisons were followed for 4 consecutive yr.
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SHOFFNER ET AL.
TABLE 2. Comparison of least squares means ± SE of quantitative traits between sibs segregating for the dominant marker1 Age at first egg
Line B-S Cp-R-U Cr-I-F D-M-Po
E W Mb Fsh
(wk) 24.1 ± .30 24.1 ± .20 25.4 ± .20 25.0 ± .20 24.3 ± .17** 23.6 ± .18 24.3 ± .22 24.9 ± .24 23.8 ± .21 24.5 ± .22 24.5 ± .10 24.6 ± .10 23.6 ± .16 23.8 ± ,10 25.3 ± .20 24.8 ± .20 25.6 ± .20 25.3 ± .20
(no.) 173 ± 4 173 ± 3 158 ± 3 169 ± 3 164 ± 3 168 ± 3 172 ± 3 168 ± 3 161 ± 3 167 ± 3 162 ± 3 159 ± 3 172 ± 3 171 ± 3 168 ± 3 167 ± 3 160 ± 3 165 ± 3
Egg weight
Body weight 8 wk
32 wk
/~\ 50 50 49 49 50 50 51 51 51 51 50 50 50 50 51 51 52 51
± .4 ± .4 ± .3 ± .3 ± .3 ± .3 ±.3 ± .3 ± .3 ± .3 ± .2 ± .2 ± .2 ± .2 ± .3 ± .3 ± .3 ± .3
y&
702 ± 9 703 ± 8 634 ± 6 645 ± 6 681 ± 5 700 ± 6 711 ± 6 700 ± 7 702 ± 7 699 ± 7 712 ± 6*** 679 ± 6 668 ± 5 675 ± 5 706 ± 5 700 ± 5 710 ± 6 710 ±7
2,233 ± 29 2,225 ± 24 2,188 ± 19 2,210 ± 19 2,243 ± 18** 2,318 ± 19 2,275 ± 21 2,245 ± 23 2,191 ± 23 2,267 ± 23 2,301 ± 19** 2,250 ± 19 2,134 ± 17 2,145 ± 17 2,312 ± 20 2,290 ± 19 2,301 ± 21 2,295 ± 21
1
The number of full-sib comparisons for each phenotypic class ranged from 304 to 613 for age at first egg, 304 to 613 for egg production, 303 to 537 for egg weight, 312 to 629 for 8-wk weight, and 306 to 614 for 32-wk weight. The total number of observations varied between 3,928 and 4,511. 2 M indicates marker, m indicates nonmarker progeny. "Comparison of marker with nonmarker progeny (P > .01). •"Comparison of marker with nonmarker progeny (P > .001).
full sibs (Table 2). Gene F is suspected as would require very tight linkage of a having the major influence, as neither Cr marker trait with major loci or alternatively nor I phenotypes have been found to have pleiotropic effects. later onset of lay. The defective feather structure alters insulating capability so Egg Weight at Thirty-Two birds are more susceptible to fluctuating Weeks of Age ambient temperatures. Hutt (1949) reported There were no differences between fulllater sexual maturity for frizzled birds. Under tropical conditions with higher am- sib segregates for egg size at 32 wk of age bient temperatures, F may be beneficial (Table 2). (Horst, 1987). Eight-Week Weight Egg Production to Fifty Weeks of Age
Birds expressing £ were distinctly heavier at 8 wk of age compared with non-E full sibs (Table 2). Comparisons cited by Smyth None of the marker traits showed a (1969) indicate variable expression for body significant association with egg numbers, size of E carriers. The RRc parent line although there was a difference of 11 eggs ranged from 50 to 100 g heavier than the E in favor of recessive full sibs versus Cp-R-U parent line at 8 wk of age. In view of this carriers that approached the 5% level of parental difference and the mating system significance (Table 2). Considering the low used to produce segregates, no contribution heritability of egg production, association from RRc additive genetic source is evident.
Downloaded from http://ps.oxfordjournals.org/ at North Dakota State University on May 24, 2015
O-P-Na
M* m M m M m M m M m M m M m M m M m
Egg production
ASSOCIATION OF PHENOTYPIC AND METRIC TRAITS IN CHICKENS
Adult Body Weight at Thirty-Two Weeks of Age
ing hypervariable DNA regions such as microsatellite polymorphisms that are nonexpressing and promise to be efficient markers for identifying regions associated with variable expression in metric traits. ACKNOWLEDGMENTS
The authors express appreciation to Phillip Lowe, Bernard Wienland, James Bitgood, and Robert Smyth for their assistance and advice. This study was made in cooperation with the North Central Regional Poultry Breeding Project 168 and is a publication of the Minnesota Agricultural Experiment Station, Scientific Journal Series Article Number 20072. REFERENCES Carefoot, W. C, 1990. Test for linkage between the eumelanin dilution blue (B/), the extended black (E) allele at the E locus and the linked pea comb (P) and eumelanin extension (Ml) genes in the domestic fowl. Br. Poult. Sci. 31:465-472. Horst, P., 1987. Animal genetic resources and potential resource development in the tropics with special references to Malaysia. Malays. Appl. Biol. 16:13-22. Horst, P., and H. W. Rauen, 1986. Significance of the naked neck gene (Na-gene) in poultry breeding in the tropics. Pages 191-195 in: Proceedings of the 7th European Poultry Conference, Vol. 1, Paris, France. Hurt, F. B., 1949. Genetics of the Fowl. McGraw-Hill Book Co. Inc., New York, NY. Kinney, T. B., Jr., and P. C. Lowe, 1968. Genetic and phenotypic variation in the Regional Red Control over nine years. Poultry Sci. 47:1105-1110. Merat, P., 1990. Pleiotropic and associated effects of major genes. Ch. 20. Pages 429-467 in: Poultry Breeding and Genetics. R. D. Crawford, ed. Elsevier, Amsterdam, The Netherlands. National Research Council, 1984. Nutrient Requirements of Poultry. 8th rev. ed. National Academy Press, Washington, DC SAS Institute, 1982. SAS® User's Guide: Statistics. 1982 ed. SAS Institute Inc., Cary, NC. Shaw, E. M., R. N. Shoffner, D. N. Foster, and K. S. Guise, 1991. Mapping of the growth hormone gene by in situ hybridization to chromosome 1. J. Hered. 82:505-508. Smyth, J. R., Jr., 1969. Relationship between genes affecting melanin pigmentation and other traits in the fowl. World's Poult. Sci. J. 25:6-14. Smyth, J. R., Jr., 1990. Genetics of plumage, skin and eye pigmentation in chickens. Ch. 5. Pages 109-167 in: Poultry Breeding and Genetics. R. D. Crawford, ed. Elsevier, Amsterdam, The Netherlands. Smyth, J. R., Jr., and F. A. Ponce de Leon, 1992.
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The E genotype was significantly heavier at adult size than non-E segregates (Table 2). On the basis of size differential at 8 wk of age, this advantage could be extended to adult body size for the E genotype. The Cr-I-F phenotypes were significantly smaller at 32 wk of age, compared with their full-sib segregates. This was not unexpected, as both I and F carriers have been found to be at a weight disadvantage in numerous comparisons (Smyth, 1969, 1990; M6rat, 1990). The Cr-I-F chicks were 19 g lighter than segregating sibs at 8 wk of age. Although this was not a significant difference at this age, it was predictive of body size difference at adult age. The fact that pleiotropic effects were expressed as expected gives credence to the validity of the design for discrimination between E and non-E phenotypes. The traits J and F were associated with pleiotropic effects as previously reported. Trait No. did not have pronounced pleiotropic effects (Horst and Rauen, 1986), evidently because of moderate temperatures as well as considerable recovery of body feathering in the backcross. The homozygous Na line had greatly reduced feathering in the pterylae and apteria body area and greatly reduced hatchability. The frequency of Cp was so low that it had little impact on variable expression for the Cp-R-U linkage group. The linkage or positive pleiotropic effect of E appears to be real and merits further exploration. Recently, Carefoot (1990) and Smyth and Ponce de Leon (1992) provided evidence that the locus for E was linked to P on Chromosome 1. Pea comb is located on the p arm and the growth hormone (GH) gene is located approximately in the G band region lg4 on the opposite arm (Shaw et al, 1991). Whether the E and GH loci are sufficiently close together for the apparent effects of E on growth to result from the GH locus is unknown, but because of chromosomal distance and high recombination rate it does not seem likely. Genetic modifications of morphological traits are generally not very efficient markers, especially when there are few. There are now available techniques for recogniz-
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Research note: Linkage between the pea comb (P) and extended black loci of the chicken. Poultry Sci. 71:208-210. Somes, R. G., Jr., 1988. International Registry of
Poultry Genetic Stocks. Storrs Agricultural Experiment Station Bulletin 476, Storrs, CT. Thoday, J. M., 1961. Location of polygenes. Nature 191:368-370.
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