White meat is the most economically valuable part of a broiler chicken. Increasing white meat relative to overall body size (white meat percentage, WM%) makes a broiler, gram for gram, a more valuable animal. However, accurately measuring WM% requires removing the bird from the breeding flock. Identification of markers for genomic regions associated with WM% would allow direct genetic selection on breeders. The objective of the current study was to identify genomic regions affecting WM% and other growth and carcass traits in an F2 cross between 2 commercial broiler lines that differed in WM%. Two commercial lines were crossed to generate 5 F1 half-sib families of each reciprocal cross type. One male from each family was crossed with 3 females from each of the other families within each reciprocal cross type. Seven F2 half-sib families, totaling 430 F2 individuals, were analyzed. Microsatellite markers (n = 73) on the 11 largest chromosomes were analyzed for associations with various growth and carcass traits by least squares interval mapping using line-cross, half-sib, combined, and parent of origin models. Sixty-eight QTL were identified at the 5% chromosome-wise level, including 6 QTL affecting WM%. Ten QTL reached 5% genome-wise significance, including 1 WM% QTL on Gga 2. The current study identified genomic regions harboring QTL affecting WM% and other carcass and growth traits, which may be useful for direct genetic selection, and also identified putative imprinted QTL in the chicken. The advantage of using multiple statistical models was evident because QTL were identified with the combined and parent of origin models that were not identified with the line-cross or half-sib models.

and Implications A joint analysis of two F2 crosses between commercially relevant breeds, Berkshire x Yorkshire, and Berkshire x Duroc, was conducted to identify chromosomal regions (quantitative trait loci or QTL) associated with growth, composition, and meat quality traits for four chromosomes. Joint analysis led to greater power to detect QTL, greater QTL mapping precision and better characterization of QTL. This enables proper definition of QTL in terms of inheritance mode of gene action and of segregation of alleles within the parental breeds, which provides valuable information for subsequent QTL analyses and marker-assisted breeding schemes. Because the populations studied were derived from commercially relevant breeds, the QTL identified have important economic effects for pork production.