Rapid duplication and loss of genes coding for the alpha chains of hemoglobin

Rapid cycles of gene duplication and loss appear to have been going on in the region coding for the alpha chain of adult hemoglobin. This is inferred from restriction endonuclease analysis of the alpha gene region in five species of apes, whose common ancestor lived about 10 million years ago. Because all five species resemble humans in having duplicate alpha genes, the duplicate state of this region is probably at least as old as the common ancestor of all these species. However, the alpha polypeptides within these species are about 10 times more alike than is expected for 10 million years of divergent evolution. Thus, the alpha polypeptides within each species have been evolving in concert. Changes in gene number have also taken place in the apes. Whereas the predominant number of alpha genes per chromosome is two for most species, it is three for chimpanzees. Concerted evolution appears also to have occurred, but far more slowly, in the region coding for the adult beta-like chains of hemoglobin. Consideration of the structural differences between the two regions leads to the hypothesis that the lengths of the noncoding regions are important determinants of the rates at which genes are gained and lost by intergenic recombination.