COMPENSATORY ASPECTS OF ALLELE DIVERSITY AT IMMUNOGLOBULIN LOCI - GENE CORRELATIONS IN RABBIT-POPULATIONS DEVOID OF LIGHT-CHAIN DIVERSITY (ORYCTOLAGUS-CUNICULUS L, KERGUELEN ISLANDS)

Is there a selective advantage of increased diversity at one immunoglo bulin locus when diversity at another locus is low? A previous paper d emonstrated excess heterozygosity at the rabbit light chain b locus wh en heterozygosity was low at the heavy chain constant region e locus. Here we consider the reverse situation by analyzing allele distributio ns at heavy chain loci in populations fixed for the light chain b locu s. We analyzed the a locus that encodes the predominantly expressed he avy chain variable region, and the d and e loci that control different parts of the Ig gamma class constant region. While there was excess h eterozygosity, genetic differentiation between localities was extensiv e and was most pronounced for females. This was in marked contrast wit h observations in areas where b-locus diversity was important and conf irms a negative correlation between e- and b-locus heterozygosity. Tri genic disequilibria corresponded to a significant negative correlation between e- and a-locus heterozygosity due mainly to strong variation among localities within the context of pronounced (digenic) linkage di sequilibria. Although substantial, the average increase in a/e-locus s ingle heterozygosity implemented by higher order disequilibria within localities was not significant.