The White Leghorn, Hy-Line layers, Avian broiler line, and several Chinese breeds were used as reference popu- lations to examine distribution profiles of genotypes and alleles in PRL and PRLR. For PRLpro2, the White Leghorn was the only +/+ line, and the Silkie and Beijing-you the only −/− breeds. Because broodiness is seldom observed in White Leghorns, the distribution profile of PRLpro2 is consistent with the observation for Blue-shell chickens that absence of the 24-bp insertion in PRL promotor is associated with the phenotypic expression of broodiness. The polymorphism for PRLpro2 was present in the other stocks, especially in Hy-Line brown egg layer, which has been intensively selected for egg production and has a low incidence of broodiness. These results imply that other genes, in addition to PRL, are involved in broodi- ness, which is consistent with the complexity of incuba- tion behavior involving the onset and maintenance of broodiness.