Question

A man possesses an allele for a recessive X-linked genetic condition, and his wife does not possess the allele. What are the odds that the couple’s son will express the condition?

Answer 1

Since the genetic condition is X-linked recessive, the son would need to inherit the allele for the condition from his mother (who is a carrier) and receive a Y chromosome from his father. The probability of the son inheriting the allele for the condition from his mother is 50% (as she is a carrier), and the probability of receiving a Y chromosome from his father is 50%.

Therefore, the odds of the couple's son expressing the X-linked genetic condition are 0.5 (50%) x 0.5 (50%) = 0.25, or 25%.