Question

Mr. Christopher is colourblind and carrier for Phenylketonuria (PKU). What percentage of sperms possesses defective allele for both?

• A. 0%
• B. 25%
• C. 50%
• D. 100%

Answer 1

Answer: (B)

25%

Colourblindness is an X linked recessive disease whereas Phenylketonuria (PKU) is an autosomal recessive trait.

Since Mr. Christopher is a carrier for PKU, this means, only one allele for PKU is present in the autosome. He is colorblind this means that he has the genotype X^cY.

The sperms produced by the man will be half carrying X chromosome and half carrying Y chromosome. This means that 50% of the sperms will be carrying the defective allele for colorblindness. Out of these 50% sperms, half of these will be having the defective allele for phenylketonuria as well i.e. 25%.

So, the correct answer is '25%'.