A man who is heterozygous for the disease haemophilia marries a woman who is double recessive for haemophilia. What percentage of their offspring would have the disease?

A man who is heterozygous for the disease haemophilia marries a woman who is double recessive for haemophilia. What percentage of their offspring would have the disease?
A. 0%
B. 25%
C. 50%
D. 75%

Correct Option: Answer is C
Let’s analyze the inheritance pattern of haemophilia:

Gene: H

H (dominant): No haemophilia
h (recessive): Haemophilia
Parents:

Man: Heterozygous (Hh)
Woman: Double recessive (hh)
Possible Offspring:

Mother’s Gene Father’s Gene Offspring Genotype Offspring Phenotype
h H Hh Normal (not affected)
h H hh Haemophilia
h h hh Haemophilia
From the table, we can see that:

50% of the offspring have the genotype Hh, which means they are carriers of the disease but do not show symptoms (normal).
50% of the offspring have the genotype hh, which means they have the disease and will show symptoms (haemophilia).
Therefore, the percentage of offspring with haemophilia is 50% (C).

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