Differences between alpha- and beta-chain mutants of human haemoglobin and between alpha- and beta-thalassaemia. Possible duplication of the alpha-chain gene.

Human adult haemoglobin consists of two unlike pairs of polypeptide chains, and can be described as alpha(2)beta(2). Amino-acid substitutions in either of the two types of chain result in alpha- and beta-chain variants. In thalassaemia, which causes a lowered production of haemoglobin, the alpha or the beta chain can be affected, the result being alpha- or beta-thalassaemia. There is a quantitative difference in the proportion of alpha- and beta-chain variants to normal haemoglobin in the respective heterozygotes, and there is also a difference in the pattern of inheritance of alpha- and beta-thalassaemia: these could possibly be explained by assuming that man has one gene for the beta- and two for the alpha-chain.