Question

Red-green colour blindness is a sex-linked inherited characteristic. The gene (allele) b for colour blindness is recessive to the gene B for normal vision. The gene b is carried only on the X chromosome.
(a) Describe these phenotypes.



(b) Explain why red-green colour blindness is more likely to occur in men than in women. [4 MARKS]

Answer 1

a) 3 Marks
b) 1 Mark

(a)
(i) Female, normal vision
(ii) Male, red-green colour blind
(iii) Male, normal vision

(b) In males, only one allele from a pair is present. So if recessive factor b is present, it will show as red-green colour blindness.