In cats, black fur color is determined by an X-linked allele; the other allele at this locus determines orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?

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Question restatement: In cats, black fur color is determined by an X-linked allele, and the other allele at that locus determines orange color. The heterozygote is tortoiseshell. What offspring would result from crossing a black female with an orange male?

Option A: orange females; black males
- This would require daughters to inherit an orange allele from the mother, which is impossible here because the mother is black and contributes only the X^B chromosome to eggs. The father can contribute an X^O or a Y, but daughters would receive X^O from father and X^B from mother, yielding tortoiseshell, not orange daughters. Thus this option is incorrect.

Option B: tortoiseshell females; tortoiseshell males
- Daughters could indeed be tortoiseshell if they get X^B from the mother and X^O from the father (X^B X^O). However, the sons would receive the mother’s X^B and the father’s Y (X^B Y), which is black, not tortoiseshell. Therefore this option misstates the expected male phenotype and is incorrect.

Option C: tortoiseshell females; black males
- This matches the classic X-linked cross: all daughters receive X^B (mother) and X^O (father), giving X^B X^O = tortoiseshell; all sons receive X^B (mother) and Y (father), giving X^B Y = black. This option is correct.

Option D: black females; orange males
- For a female to be black, she would need X^B X^B, which is not possible from this cross because daughters get one X from the father, which is X^O, not X^B. Likewise, orange males would require the mother to contribute X^O, which she cannot in this cross. This option is incorrect.

Summary: Evaluating each choice shows that only Option C correctly describes the offspring: tortoiseshell females and black males. The other options mix incompatible inheritance expectations for an X-linked color system in cats.

Bio 93 Section CDE 2025 Final Exam Practice, Part 1

In cats, black fur color is determined by an X-linked allele; the other allele at this locus determines orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?

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