EVIDENCE FOR BALANCING OF HM, BUT NOT GM, ALLELES BY HETEROTIC ADVANTAGE IN SOUTH AMERINDS

Two KM alleles occur in 1075 South Amerinds of 14 tribes in approximat ely balanced and uniform frequency. However, the number of heterozygot es is 12.7% greater than expected by frequency analysis and 16.5% grea ter by segregation analysis. This excess is evident in children 0-4 ye ars of age and may reflect either prenatal or early childhood selectio n. The frequencies of GM haplotypes were different, and quite uniforml y so, in diverse tribes, Most GM heterozygotes can only be distinguish ed from GM 1,2,17 21 homozygotes by DNA or family relationship. No def icit of GM homozygotes was observed in 119 children in whom heterozygo sis was determined by family. Thus, the KM polymorphism, like HLA, may be maintained by preferential survival of heterozygotes, but GM proba bly depends on another mechanism.