Incidence of colourblindness among four endogamous nomadic groups: an example of natural selection

Abstract

Incidence of colourblindness among 1501 (945 males and 656 females) persons belonging to four nomadic Mendelian isolates, the Nandiwallas of Maharashtra, India, has been reported. Out of the four groups, three lacked the gene for colourblindness, while in one group the incidence was rather low (0.3 per cent). Our findings support the differential selection hypothesis for this loci of Post (1962) and Pickford (1963). 110 families with 334 children were examined for the inheritance of this trait. All matings except one were of the type normal x normal and produced all normal children; the one family of the type father colourblind x normal mother, also had all the six children with normal colour vision. The implications of the loss of the colourblind gene has been discussed in the light of nomadic way of the Nandiwallas, and also of their small effective population sizes.