A woman whose father had hemophilia A (X-linked recessive) marries an unaffected man. What is the probability their first son is affected?
- A
(mother does not carry the allele)
- B
(recessive Mendelian)
- C
(X-linked traits skip a generation)
- Dcheck_circle
(mother is obligate carrier; sons get X from her)
Explanation
Father with hemophilia → his daughter inherits his X with the allele → she is an obligate heterozygous carrier. Each son gets one X from her: 1/2 chance of the affected allele.