Major histocompatibility genes in egg-laying hens.

A common base population of White Leghorn was "synthesized" for a joint project on the genetics of egg-laying, undertaken by animal breeding geneticists in 4 Scandinavian countries. After 6 to 7 generations of line selection for various egg-laying parameters, MHC typing was undertaken of both the selection lines in Denmark, Norway, and Sweden and the respective control lines representing the common base population. Ten MHC haplotypes were defined which jointly accounted for about 95% of the MHC gene pool of the base population. The 2 haplotypes which were predominant in the base population, B15 and B19, responded very differently to the selection pressures applied.