DIVERGENT SELECTION FOR HUMORAL IMMUNE RESPONSIVENESS IN CHICKENS - DISTRIBUTION AND EFFECTS OF MAJOR HISTOCOMPATIBILITY COMPLEX TYPES

Chickens were selected for 10 generations for high and low antibody re sponse to sheep red blood cells; in addition, a randombred control lin e was maintained. All birds (n = 1602) from the 9th and 10th generatio ns were typed for major histocompatibility complex B-types. All identi fied types were present in the control line but the selected lines sho wed divergent distributions. The 121 B-haplotype was predominant in th e high line in the form of 121-121 B-genotype, whereas the 114 B-haplo type was most frequent in the form of 114-114 and 114-124 B-genotypes in the low line. To explain these frequency changes, effects of B-geno types on the selected trait were estimated, using a mixed animal model . The B-genotypes were responsible for a significant part of variation of the trait within lines, but their effects differed between lines. These effects could be related partly to the changes in B-genotype dis tribution.