MCAT Biology Question 168: Answer and Explanation

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Question: 168

3. If a male with hemophilia (X_hch

A. 0%
B. 25%
C. 50%
D. 100%

Correct Answer: C

Explanation:

The female in this example is a carrier of two sex-linked traits; based on her genotype, the affected alleles are found on different X chromosomes. Drawing out a Punnett square, we see that 25% of the offspring will be female hemophiliacs (X_hX_h) and 25% will be female carriers of both alleles (X_cX_h). This question is asking what percentage of females will have a normal phenotype, which would be half of the females (those who are carriers for both traits).

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