Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: April 24, 1997
Publication Date: N/A
Nine Dorset rams of CLPG phenotype and 114 Romanov ewes were used to develop a resource flock of 355 F2 lambs segregating for the CLPG allele to provide genotypic and phenotypic data to estimate chromosomal position, test gene action, and quantify allelic effects of genotypes on carcass traits. The parent generation consisted of matings of eight F1 sires and 138 F1 dams. Lambs were serial slaughtered in six groups at 3-wk interval starting at 23-wk of age to estimate accretion rates of carcass components. A linkage group of 22 loci (mean of 720 informative meioses/marker) spanned 86.3 centimorgans (cM) of ovine chromosome 18. Probabilities for each genotype at the CLPG locus were calculated at 1 cM intervals (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 age at slaughter. Contrasts 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)/3], where 'A'=CLPG allele, was the only significant contrast. A 3 df F-test of PO from an analysis of total carcass fat-free soft tissue regressed on carcass 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 %, 1.35; length -.82; loin area, 2.07; protein, 1.13; water, 1.03; fat, -1.26; ash, -.03, respectively. These results, based on analysis of genotypic probabilities and quantitative trait data, confirm assignment of CLPG locus to telomeric region of chromosome 18 and support the polar overdominance model of gene action.