"Private" genetic variants and the frequency of mutation among South American Indians.

Electrophoretic studies were performed on 15 proteins of blood serum and of erythrocytes, from blood specimens from 72 villages of six relatively unacculturated and genetically pure Indian tribes of South America, for a total of 56,237 determinations. At least 10 different "private" variants were encountered, in 131 people. Two previously recognized genetic polymorphisms of these 15 proteins were also encountered. On the assumption that these variants are neutral from the standpoint of natural selection, and that only one-third of amino-acid substitutions in proteins result in electrophoretically detectable variants, the mutation rate is estimated from a formulation of Kimura and Ohta to be about 8 x 10(-5) per locus per generation. The calculation involves several approximations which can be improved by further investigations; if confirmed, then for this class of mutations Indian mutation rates are roughly an order of magnitude higher than commonly envisioned.