Mapping of Main-Effect and Epistatic Quantitative Trait Loci for Internal Egg Traits in an F2 Resource Population of Chickens

Quantitative trait loci (QTLs) analyses for internal egg quality of chickens were performed with 143 microsatellite markers on 27 linkage groups in 371 F-2 hens obtained from an intercross between Japanese Large Game (Oh-Shamo) and White Leghorn breeds. Internal egg traits, such as weight and size of the albumen, weight and size of the yolk, and yolk colors, were measured in three different egg laying stages (early, middle, and late stages). We detected 11 significant and four suggestive QTLs with main effects on 27 internal egg traits in the three stages. Albumen weight and size QTLs were identified on chromosomes 1, 2, 4, 5, 6, 8, 9, 27, and Z. Yolk weight and size QTLs were discovered on chromosomes 4, 7, 8, 15, and Z, whereas yolk color QTLs were detected on chromosomes 1, 3, 4, 8, 9, and 27. Moreover, we revealed four significant and two suggestive QTLs with epistatic interaction effects on three internal egg traits in the late stage. This is the first report of epistatic QTLs for internal egg traits in chickens. The four significant loci were on chromosomes 1, 2, 8, and 17 and affected yolk size and yolk color, whereas the two suggestive loci were located on chromosomes 2 and 10 and affected albumen height. Among these epistatic QTLs, the two QTLs detected on chromosomes 1 and 8 were found at the regions of main-effect QTLs. The present main and epistatic QTLs accounted for 3.61-18.46% of the phenotypic variances. The chromosomes 1 and 8 QTLs with main effects on internal egg traits exerted their effects throughout all three stages, whereas the other QTLs with main- or epistatic-effects were detected in one or two stages. These results demonstrated that age-related changes of QTLs will make the genetic features of quantitative traits more complex.