Random mating and selection in families against homozygotes for HLA in south Amerindians.
We have examined HLA-A and HLA-B in a large sample of families of South Amerindians for non-random mating and for Mendelian segregation in their progeny. The proportion of couples sampled for mating averaged over 50% of the total matings with progeny for 10 of the 11 tribes with 10 or more known matings. In nearly all cases, HLA-sharing proportions were very close to those expected from random mating, suggesting strong negative-assortative mating for MHC is not present in these South Amerindians. In progeny from these matings and others in 23 tribes, there was a large deficiency of homozygotes (excess of heterozygotes) compared with Mendelian expectations. In particular, there was a deficiency in all types of matings except when the female was a homozygote and the male shared one allele with her; the reciprocal mating showed no such deficiency. This non-reciprocity suggests the importance of some type of maternal-fetal interaction. A model to describe these results showed very surprising properties for two alleles: no change in allelic frequency like neutrality, an excess of heterozygotes like heterozygote advantage, and a minimum fitness at intermediate allelic frequency like heterozygote disadvantage. For three or more alleles, the model has the qualities of a traditional balancing selection model.
Hedrick
P W
PW
Department of Biology, Arizona State University, Tempe 85287, USA. hedrick@hedricklab.la.asu.edu
Black
F L
FL
D000293:Adolescent; D000328:Adult; D000483:Alleles; D001938:Brazil; D002648:Child; D002675:Child, Preschool; D003469:Culture; D005260:Female; D005805:Genes, MHC Class I; D005838:Genotype; D015234:HLA-A Antigens / Q000235:genetics*; D015235:HLA-B Antigens / Q000235:genetics*; D006801:Humans; D007199:Indians, South American / Q000235:genetics*; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008393:Marriage; D008875:Middle Aged; D011247:Pregnancy / Q000276:immunology; D012641:Selection, Genetic
D015234:HLA-A Antigens; D015235:HLA-B Antigens