Genetic architecture of growth and body composition in unique chicken populations

A resource population was established by crossing one modern broiler sire from a commercial broiler breeder male line with dams from two unrelated highly inbred lines; F-2 birds were intercrossed to produce two F-2 populations. A variety of phenotypic measurements related to growth, muscling, internal organs, and skeleton were recorded for the F-2 populations and contemporary pure inbred and broiler birds. Based on the means and phenotypic distributions of the F-2 populations compared to their parental lines, the effective number of genes affecting each trait and heterosis were estimated and discussed relative to the known genetic selection history for each trait. The results suggest that a high number of genes with small epistatic effects are involved in determining the phenotype for traits that broilers were traditionally selected for, and a lower number of genes with major effects are involved in determining the phenotype for traits related to fitness. The estimated number of genes and the phenotypic distributions of the different traits suggest that a quantitative trait loci (QTL) search might be more effectively applied for traits with a low number of involved genes and a high phenotypic distribution among the F-2 birds than for traits that show a lower phenotypic distribution and a high number of genes.