Hemophilia A is an X-linked recessive trait in which the blood does not clot properly. An unaffected mother and a father with hemophilia have a daughter with hemophilia. Their next offspring is a son named Dan. What is the likelihood that Dan has hemophilia?

Question

BlackTom AI · Accepted Answer

X-linked recessive inheritance: males are affected if they inherit one mutant X (XhY), while females must inherit two mutant Xs (XhXh) to be affected. An affected daughter (XhXh) requires that the father contributed Xh and the mother contributed Xh, so the mother must be a carrier (XHXh) even though she is phenotypically unaffected.

Parental genotypes implied by the information:
- Father: XhY (affected)
- Mother: XHXh (unaffected carrier, inferred because they have an affected daughter)

List parental gametes:
- Mother produces eggs XH and Xh (each with probability 1/2).
- Father produces sperm Xh and Y (each with probability 1/2).

Full Punnett square (all offspring, but we will focus on sons):
- XH (egg) × Xh (sperm) → XHXh (carrier daughter, unaffected)
- Xh (egg) × Xh (sperm) → XhXh (affected daughter)
- XH (egg) × Y (sperm) → XHY (unaffected son)
- Xh (egg) × Y (sperm) → XhY (affected son)

For a son (Dan) the father must have supplied the Y chromosome. That restricts outcomes to the two male outcomes:
- Mother XH + Father Y → XHY (unaffected son)
- Mother Xh + Father Y → XhY (affected son)

Each of these male outcomes is equally likely because the mother’s egg is equally likely to be XH or Xh. Therefore probability Dan is affected = 1/2 = 50%.

Why other choices are incorrect:
- 0%: impossible because the mother must be a carrier (we observe an affected daughter).
- 25%: would be a typical probability for an autosomal recessive child when both parents are carriers, not applicable here.
- 100%: would require the mother to be affected herself (XhXh), which she is not.

Final answer confirmed: 50%.

Hemophilia A is an X-linked recessive trait in which the blood does not clot properly. An unaffected mother and a father with hemophilia have a daughter with hemophilia. Their next offspring is a son named Dan. What is the likelihood that Dan has hemophilia?Single choice

Similar Questions

If a woman with a disease trait, which is X-linked recessive, has children with an unaffected male, which of the following statements would be most accurate?

Female fruit flies homozygous for the X-linked white-eye allele (XWXW) are crossed to males with red eyes (XW+Y). On rare occasions, an offspring is a male with red eyes. This rare offspring is most likely ( _______) due to non-disjunction during ( ).

If a female chimpanzee that is heterozygous for red-green color blindness (a recessive X-linked mutation) is crossed with a wild-type male, what predicted proportion of the progeny will be females that display the mutant phenotype?

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 at position 44 A man will pass on an allele of an X-linked gene to:all of his daughtershalf of his sonsall of his sonshalf of his daughtersall of his children

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?

More Practical Tools for Students Powered by AI Study Helper

Homework AI Solver

Stylized AI Paper Writer

Plagiarism Checker Assistant

Citation AI Academic Writing Tool

In-Class Translation Assistant

AI Note Generator

AI Quiz Answers

Past Exam Questions from University Test Bank

Smart Practice Assistant

Adaptive Practice

Making Your Study Simpler