Hemophilia is an X-linked recessive bleeding disorder in humans. If a carrier mother () and a normal father () have children, what is the probability that a son will be hemophilic?
Answer and explanation
Correct answer: D. of sons
- Step 1: The mother has genotype , meaning half of her ova carry the normal allele and half carry the mutant allele .
- Step 2: Sons receive their single X chromosome from their mother and their Y chromosome from their father ( or ).
- Step 3: Among all male offspring, receive and are normal (), while receive and express hemophilia ().
Answer
of sons.
Why not the others: of sons would require an affected hemophilic mother (); represents the risk among all four children regardless of sex; would require a homozygous normal mother ().
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