Question

The mode of inheritance of familial adenomatous polyposis is

• A. autosomal dominant
• B. autosomal recessive
• C. X linked recessive
• D. polygenic

Hint:

Recall which tumour suppressor gene mutation underlies this polyposis syndrome and how many copies need to be abnormal.

Answer 1

The Correct Option is A

This question is really testing whether you know FAP is caused by a single dominant tumour-suppressor mutation.

1. autosomal dominant: correct. One mutated APC allele is enough to cause the disease, and it is transmitted with 50 percent risk to each offspring regardless of sex.
2. autosomal recessive: wrong. This pattern needs two mutated copies, which describes a different and rarer polyposis syndrome, not classic FAP.
3. X linked recessive: wrong. FAP affects males and females equally and can pass from father to son, which rules out X-linked inheritance.
4. polygenic: wrong. FAP results from a mutation in a single gene, APC, not the cumulative effect of many genes.

Correct answer: autosomal dominant