Quantitative Trait Loci Mapping for External Egg Traits in F2 Chickens

Quantitative trait locus (QTL) mapping of external egg traits in chickens was carried out with 143 microsatellite markers using 388 F-2 hens obtained from an intercross of a Japanese Large Game (Oh-Shamo) male and three White Leghorn females. External egg traits, such as the weight and length of eggs and the weight, thickness, strength, and color of eggshells were measured at three different stages of egg production, i.e. early, middle, and late stages. QTL analyses revealed 10 significant and three suggestive QTLs with main effects on external egg traits on chromosomes 1, 2, 4, 5, 8, 10, 11, 12, 17, and Z. The QTL alleles derived from Oh-Shamo, one of the indigenous Japanese breeds, uniquely increased most external egg traits, whereas some QTL alleles had opposite effects on phenotypic differences between Oh-Shamo and White Leghorn. The QTLs detected accounted for 3.09-15.39% of the phenotypic variances. Although the QTLs on chromosomes 5, 8, and Z were found throughout all three stages, the others were identified at only one or two stages. Epistatic QTLs for external egg traits were not detected in the present study. The age-related changes of our main-effect QTLs illustrate one aspect of the complex genetic basis of external egg traits.