The DNA sequences which produce our haemoglobin, the alpha and beta genes, started out as sisters. About half a billion years ago, in an early fish (perhaps of the ostracoderm or placoderm grade that we described previously), an ancestral globin gene accidentally duplicated, both copies remaining in that fish’s genome. One copy was destined to give rise to the alphas, on what would eventually become chromosome 11 in our genome, the other to the betas, now on our chromosome 16.
