A woman who is a carrier for colour blindness (X-linked recessive) has children with a man who has normal colour vision. A. What are the genotypes of the man and woman? (2 marks) B. What percentage of their children do you expect to be colour blind? (1 mark) C. What proportion of their children will be carriers of the allele for colour blindness? (1 mark) D. Is it possible for the couple to have a girl who is colour blind? Why or why not? (2 marks)

Since the allele for the color blindness is carried on one of the X -chromosomes of the carrier mother, then the male children will be color blind or carrier deopending on the defective gene they inherited. Since they will receive the defective or normal allele from the mothers,but the female will carriers or normal because they will inherit either defective allele or normal allele from the mother,but normal X allele from the father.

Assuming the colorbind gene was inherited by One of the boys, and the girls take the defective genes

1. XNY vs XCbXN.Then the one of the boys will be colorblind and the one of girls will be carriers. XNXCb, XNXN, XCbY,XNY 50 %

2.If the two boys take the effective genes from the mothers. and none of the girls take the defective alelle

Then the two boys will be colorblind and the girls will be carrries XcbY,XcbY and XNXN XNXN.(normal girls).

The proportions that will be the females since the girls can only take the defective allele from one of the normal and defective allele from the mother. Assuming the girls take the defective allele from the mothers and take normal from the father,they will all be carriers,since the X of the father is normal.

They can not have a color blind girl.Since the father is normal It takes two colorblind X-chromosome to give a girl.