Frank’s sister is known to carry an allele for a single-gene recessive genetic disorder that is fatal in very early life. Frank’s mother was tested for the allele and found not to carry it. What are the odds that Frank is a carrier for the allele?

Question

Frank’s sister is known to carry an allele for a single-gene recessive genetic disorder that is fatal in very early life. Frank’s mother was tested for the allele and found not to carry it. What are the odds that Frank is a carrier for the allele?

Correct Answer(s)
1/1
Press Space to open
1/4
Press Space to open
1/2
Press Space to open
1/8
Press Space to open
Incorrect Answer(s)

Answer 1

1/4

Explanation:
Since Frank's mother was tested and found not to carry the allele, the only way for Frank to be a carrier is if his father carries the allele. Since the disorder is a single-gene recessive disorder, Frank must have inherited one recessive allele from his father in order to be a carrier. This means that Frank's father must be a carrier for the allele. Therefore, the odds that Frank is a carrier are 1/2.