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Evaluation of a major gene affecting carcass composition of sheep
Abstract
Nine Dorset rams expressing an extreme heavy muscled phenotype, callipyge (CLPG), exposed to 255 Romanov ewes with normal phenotypes, comprised the grandparent generation of a resource flock developed to estimate chromosomal position, test gene action, and quantify allelic effects of genotypes at the CLPG locus on carcass traits. The parent generation consisted of eight F$\sb1$ sires and 138 F$\sb1$ dams inter se mated for two replicate seasons to produce 432 F$\sb2$ progeny. Carcass data were obtained from 355 F$\sb2$ lambs serially slaughtered in six groups at 3-wk intervals starting at 23 wk of age to estimate accretion rates of carcass tissues. A linkage group was constructed for ovine chromosome 18 and consisted of 22 marker loci spanning 86.3 centimorgans (cM). Probabilities for each genotype at the CLPG locus were calculated at intervals of 1 cM (0-106). Contrasts of genotypic probabilities produced coefficients to evaluate alternative models for gene action. Statistical models developed fit effects of sex, year, sires, and contrast-specific linear and quadratic regressions on the appropriate covariable. Various genetic models tested included additive, maternal dominance, and paternally derived polar overdominance (PO) effects. Lack of fit F tests (3 df) indicated PO (Aa - (AA + aA + aa)), where 'A' = CLPG allele, was the only significant contrast. A 3-df F test of PO from an analysis of fat-free soft tissue regressed on fat was maximum at position 91 cM (F = 43.3; $P<.0001$). Residual standard deviation units for PO at position 91 cM and 215 d age were for carcass: weight,.20; dress percentage, 1.35; rib fat, -.94; thoracic fat, -.63; length, -.82; loin area, 2.07; leg score, 3.16; marbling score, -1.66; shear force, 1.91; protein, 1.13; water, 1.03; fat, -1.26; and ash, -.03, respectively. These results, based on analysis of genotypic probabilities and quantitative trait data, confirm the assignment of the CLPG locus to the telomeric region of chromosome 18 and support the polar overdominance model of gene action.
Subject Area
Genetics|Livestock
Recommended Citation
Freking, Brad Allen, "Evaluation of a major gene affecting carcass composition of sheep" (1997). ETD collection for University of Nebraska-Lincoln. AAI9725121.
https://digitalcommons.unl.edu/dissertations/AAI9725121