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 scheme. Animals were either typed for two polymorphic marker loci, 20 centimorgans apart, flanking a single biallelic quantitative trait locus and were evaluated using a model accounting for marker information, or animals were not typed but were evaluated by a conventional BLUP animal model. Selection was for a single trait measured on females, and each dam had 4 sons and 4 daughters. Nucleus foundation animals were chosen from a base population in linkage equilibrium. With the favorable allele at an initial frequency of 0.5, marker-assisted selection substantially increased responses at the quantitative trait locus but reduced the polygenic responses. Cumulative genetic gain increased by up to 3, 9, 12, and 6% after one, two, three, and six generations of selection, respectively. If the favorable allele was initially rare (frequency of 0.1), the merits of marker-assisted selection were even more pronounced (genetic gains increased by up to 9, 19, 24 and 15%, respectively). The superiority of marker-assisted selection over conventional BLUP increased when a restriction was placed on selection of full brothers and decreased when variance of the quantitative trait locus used in the evaluation model was overestimated.