The evolution of the alpha- and beta-globin gene clusters in human populations

DNA analysis of the alpha- and beta-globin gene clusters has revealed substantial variability between individuals and populations. As well as restriction enzyme site and length polymorphisms, variation in gene copy number and type is observed. Because of this extensive polymorphism DNA analysis offers a highly informative method of studying genetic affinities between human populations. Haplotypes, consisting of a set of restriction enzyme polymorphisms distributed along the cluster, have been developed for both loci. Analysis of the molecular basis of numerous beta-thalassaemia alleles has revealed, in general, different sets of mutations in different populations, indicating that these postdate the racial divergence. Recent microepidemiological studies on the distribution of alpha-thalassaemia support the hypothesis that this condition, like the beta s-mutation, has been selected because it confers protection against malaria. Population-specific DNA polymorphisms at these and other loci promise to be of considerable value to genetic anthropology.