When wild type females are bred to hemizygous males, what percentage of the offspring can be expected to have the transgene?

• A. 10%
• B. 25%
• C. 50%
• D. 100%

Answer: (C)

X-linked inheritance is at play here. A wild-type female is XX, and a hemizygous male carries the transgene on his single X (X^T Y). Daughters receive the X from both parents, so they get X^T from the father and a normal X from the mother, making all daughters transgenic (X^T X). Sons receive the Y from the father and the X from the mother, which is without the transgene, so none of the sons carry it. Since half the offspring are daughters and half are sons, about 50% of the total offspring will have the transgene.