Genetic investigations in a Northern Brazilian island. II. Random drift.

18 albinos were born on Lençóis island. Since 3 of them died and 5 emigrated, the prevalence of albinism is about 3% in the island. 2 inbred brothers with brachydactyly of the index fingers and 1 case of 'achondroplasia' were also found. The analysis of the population structure of the island suggests that its high frequency of albinism may have been produced by random drift. The index of isolation of its present population is roughly 17--27. Genealogical, clinical and histological data are presented and anslyzed. Natural selection is not acting against the albinism gene at a measurable rate. Cytogenetic investigations among albinos and normals did not reveal any difference as regards frequency of aneuploidy, association of acrocentrics and chromatid gaps. The role of random processes in evolution is mentioned and the possibility that they may be more important than it is sometimes assumed is stressed.