Question Detail
Question
Joseph expressed hypertrichosis (hairy pinna), a trait carried by a gene on his Y chromosome. What is the chance that his grandson will inherit the trait from him?
Correct Answer
Option C is the correct answer.
Detailed Explanation
This is a Y-linked trait. Joseph (XY with the trait) will pass his Y chromosome to all his sons. Therefore, 100% of his sons will have the trait. Each of these sons will then pass their Y chromosome (with the trait) to 100% of their sons (Joseph's grandsons). However, the question asks for the chance that a grandson inherits it specifically from Joseph. Joseph's son (who has the trait) has a 50% chance of passing his Y chromosome to a child (making it a grandson). Thus, the chance is 100% (son gets it) * 50% (grandson gets it from that son) = 50%.
Hint
Trace the Y chromosome. Does Joseph pass it to his son? Does his son then pass it to his son?