Question

The tumor suppressor gene APC, when mutant, causes a precancerous condition called familial adenomatous polyposis (FAP). FAP has autosomal dominant inheritance.
What is the probability that two individuals who are heterozygous for the APC mutation would have four children, all without the APC mutation?

• A. 1/64
• B. 0.25
• C. 1/16
• D. 0.125
• E. 0.5

Answer 1

The correct option is B 0.25

Since FAP (familial adenomatous polyposis) has autosomal dominant inheritance, so individuals with AA or Aa genotype will be APC mutant and those with aa genotype will be normal or without APC mutation.

The cross can be represented as shown in the figure.

Hence probability for the children that will be born without APC mutation is:

No. of children with aa genotype/ Total no. of children with all possible genotypes

= 1/4

= 0.25

So, the correct answer is '0.25'.