MARKER-ASSISTED SELECTION FOR A SEX-LIMITED CHARACTER IN A NUCLEUS BREEDING POPULATION

The benefits of marker-assisted selection were examined by simulation of an adult multiple ovulation and embryo transfer nucleus breeding sc heme. Animals were either typed for two polymorphic marker loci, 20 ce ntimorgans apart, flanking a single biallelic quantitative trait locus and were evaluated using a model accounting for marker information, o r animals were not typed but were evaluated by a conventional BLUP ani mal model. Selection was for a single trait measured on females, and e ach dam had 4 sons and 4 daughters. Nucleus foundation animals were ch osen from a base population in linkage equilibrium. With the favorable allele at an initial frequency of 0.5, marker-assisted selection subs tantially increased responses at the quantitative trait locus but redu ced the polygenic responses. Cumulative genetic gain increased by up t o 3, 9, 12, and 6% after one, two, three, and six generations of selec tion, respectively. If the favorable allele was initially rare (freque ncy of 0.1), the merits of marker-assisted selection were even more pr onounced (genetic gains increased by up to 9, 19, 24 and 15%, respecti vely). The superiority of marker-assisted selection over conventional BLUP increased when a restriction was placed on selection of full brot hers and decreased when variance of the quantitative trait locus used in the evaluation model was overestimated.