Question

What is the approximate risk of genetic diseases in a consanguineous marriage between first cousins?

• A. 1-2%
• B. 4-8%
• C. 8-10%
• D. 12-14%

Hint:

First cousin risk is roughly double the general 2-3% birth defect rate.

Answer 1

The Correct Option is B

Step 1: Consanguinity is marriage between relatives, and closely related partners share more alleles, so their children are more often homozygous for recessive alleles.
Step 2: Because of this, the frequency of congenital malformations among newborns of first cousin unions is about double that of the general population.
Step 3: The background rate of birth defects in the general population is roughly 2 to 3 percent. Doubling this gives about 4 to 6 percent for first cousin couples.
Step 4: Among the options, the band that contains this 4 to 6 percent figure is 4-8 percent, so that is the answer.