Which of the following children will inherit an X-linked recessive allele from a woman who is heterozygous for color blindness (assuming the man is not a carrier: XNY)?

Question

BlackTom AI · Accepted Answer

Let's lay out the scenario and options clearly. A woman is heterozygous for color blindness, so her genotype is X^N X^c (where X^c carries the color-blind allele) and the man is not a carrier and has a normal X, so X^N Y.

Option 1: 'all of her sons' — This would require every son to inherit the color-blind allele from the mother. Since sons receive the Y chromosome from the father and the X chromosome from the mother, only half of the mother's eggs carry X^c (the other half carry X^N). Therefore, only about half of the sons would receive X^c and be color-blind; saying all sons would be incorrect.

Option 2: 'all of her daughters' — Daughters receive one X from the father (which is X^N because the father is not a carrier) and one X from the mother. Because the mother is X^N X^c, half of her eggs carry X^c and half carry X^N. Thus, not all daughters will inherit X^c; only about half would, so this option is incorrect.

Option 3: 'half of her daughters' — This correctly reflects the inheritance pattern for X-linked traits when crossing a heterozygous mother (X^N X^c) with a normal father (X^N Y). For daughters, the paternal X is always X^N, while the maternal contribution is X^N or X^c with equal probability. Consequently, half of the daughters will inherit X^c from the mother and become carriers (X^N X^c). This option captures the correct probabilistic outcome for daughters.

Option 4: 'none of her sons' — This is incorrect because there is a 50% chance that a son will receive the X^c from the mother, resulting in a color-blind son (X^c Y). Therefore, it is not true that none of the sons inherit the allele.

In summary, considering the parental genotypes and how X-linked inheritance works, the pattern shows that the allele is passed to about half of the daughters (as carriers) and half of the sons (as affected), with the specific statement that half of her daughters inherit the allele being a correct depiction among the given choices.

Bio 93 Section CDE 2025 Final- Section E

Which of the following children will inherit an X-linked recessive allele from a woman who is heterozygous for color blindness (assuming the man is not a carrier: XNY)?

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