Question at position 19 In cats, black fur color is caused by an X-linked allele; the other allele at this locus causes orange color. The heterozygote is tortoiseshell (due to Barr bodies). What kinds of offspring would be expected in a litter from mating a black female and an orange male?orange females; orange malestortoiseshell females; black malestortoiseshell females; orange malesorange females; black malestortoiseshell females; tortoiseshell males

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BlackTom AI · Accepted Answer

Question context: In cats, fur color is X-linked with two alleles at the same locus—orange (O) and black (B). The heterozygote X^B X^O expresses tortoiseshell due to X-inactivation. We’re crossing a black female with an orange male.

Option 1: orange females; orange males. This would require daughters to inherit an orange allele from the mother, but the black female is X^B X^B and can only pass X^B. Therefore, daughters cannot be orange, and this option is impossible.

Option 2: tortoiseshell females; black males. Daughters receive one X from each parent. From the mother (black female), every daughter gets X^B. From the father (orange male), every daughter gets X^O. So daughters are X^B X^O, i.e., tortoiseshell females. Sons receive the mother’s X and the father’s Y, giving X^B Y, which is black males. This option matches the expected outcome.

Option 3: tortoiseshell females; orange males. While daughters being tortoiseshell is correct, a son would need an X^O from the mother to be orange, which is impossible because the mother is X^B X^B and can only contribute X^B. Hence this is incorrect.

Option 4: orange females; black males. As above, daughters cannot be orange given the mother’s genotype, so this is incorrect. Sons being black is possible, but the female part rules this out.

Option 5: tortoiseshell females; tortoiseshell males. Daughters being tortoiseshell is correct, but a tortoiseshell male would require a son with one X from the mother and a second X from the father or an unusual nondisjunction event; under standard single-gene X-linked inheritance with the stated cross, a tortoiseshell male cannot arise. Therefore this option is not correct.

Summary: The compatible and expected litter composition from this cross is tortoiseshell females and black males, which aligns with typical X-linked color inheritance in cats.

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