CSEC Biology · May/June 2017 · Paper 2 · Question 4(b)

A certain form of colour-blindness is inherited as a recessive allele carried on the X chromosome. It is thus said to be 'X-linked' or 'sex-linked'. A woman with normal colour vision, whose father is colour-blind, mates with a colour-blind man. What is the chance of them having colour-blind children? Use a genetics diagram to explain your answer. Use B for the allele for normal vision and b for the allele for colour-blindness.