Question

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? B. What percentage of their children do you expect to be colour blind? C. What proportion of their children will be carriers of the allele for colour blindness? D. Is it possible for the couple to have a girl who is colour blind? Why or why not?

Answer 1

Answer:

A. $X^CX^c$

B. 1/4 or 25%

C. 1/4 or 25%

D. No

Explanation:

Let the allele for color blindness be represented by c.

A. The genotype of a woman that is a carrier for color blindness = $X^CX^c$

   The genotype of a man with normal color vision = $X^cY$

Crossing the two in a marriage:

                    $X^CX^c$      x      $X^cY$

             $X^CX^c$      $X^CY$    $X^cX^c$    $X^cY$

From the result of the cross:

B. 1/4 or 25% of their children are expected to be color blind.

C. 1/4 or 25% of their children are expected to be carriers of the allele for color blindness.

D. No. The couple cannot have a girl that is color blind. Their female children could either be totally free of the color-blindness allele or be a carrier.