The origin of mutant beta-globin genes in human populations.

The discovery that mutant beta-globin genes arise on different chromosomal backgrounds has allowed studies of the origin and spread of some of the common haemoglobinopathies. The beta S mutation has a wide geographic distribution and is found on many different haplotypes, suggesting that it has had multiple independent origins. In contrast, the Indian beta 0 deletion thalassaemia has a restricted geographic distribution and is present on a single haplotype, suggesting a single origin. The limited evidence for the beta-thalassaemia mutations indicates that most have had a single origin and have subsequently reached polymorphic frequencies by selection pressure from malaria.