The distribution of haptoglobins, transferrins and serum pseudocholinesterase in 1353 Mexican Indians belonging to 13 tribes is described. The frequency of the Hp1 gene is variable; it ranges from 0.40 to 0.65, although the majority of values fall between 0.50 and 0.65. The reason for this variability is obscure; there is no correlation between Hp1 values and linguistic affinities or habitat, and different degrees of nonIndian admixture are not accountable for the situation. It is suggested that possibly the main factor determining the present day distribution is the founder effect.
Only 16 individuals have a transferrin different from C; in two, the CD phenotype is seen and the rest belong to the BC variety. Ten of the latter identified as B0–1C, are found in a single tribe, the Cora. The scarcity of unusual transferrins in the Amerindians is corroborated in this study, although it may be somewhat unusual that the majority of them are of the fast moving type rather than of the more common slow moving type.
The overall frequency for the atypical pseudocholinesterase gene is of 0.005 and therefore lower than that found in most other populations, except for two Venezuelan and two Bolivian tribes where the atypical gene is absent. Thus, present findings suggest that the atypical gene was either absent or had a very low frequency in the ancestors of present day Amerindians.