The linkage between the genes for colour-blindness and haemophilia in man

It is well established that colour-blindness and haemophilia are due to sex-linked genes. These genes appear to manifest themselves in all males who carry them. In women the gene for haemophilia is probably always recessive, the cases of alleged haemophilia in heterozygous women being very doubtful. On the other hand, colour-blind women whose putative fathers are not colour-blind occur too frequently to be explained by illegitimacy (Bell 1926). So colour-blindness is probably not always recessive. On the other hand, women homozygous for the gene appear always to be colour-blind. No cases of incomplete recessiveness occur in the new pedigrees here presented. It will be assumed th at a woman who is not colour-blind is not homozygous for the gene for colour-blindness. There are two distinct forms of colour-blindness, namely protanopia (“red-blindness”) and deuteranopia (“green-blindness”). According to Waaler (1927) the genes determining them form a series of five allelomorphs with the normal gene, and those for protanomalia and deuteranomalia. Haldane (1935) suggested that there are at least two different allelomorphic genes for haemophilia.