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Haemophilia is more commonly seen in human males than in human females because -
A
This disease is due to a Y-linked recessive mutation
B
This disease is due to an X-linked recessive mutation
C
This disease is due to an X-linked dominant mutation
D
A greater proportion of girls die in infancy
Detailed Solution
Haemophilia is a sex-linked recessive disease: the gene is located on the X chromosome.
A male has only one X chromosome (XY), so a single recessive allele ($X^hY$) is enough to make him haemophilic; there is no second allele to mask it.
A female has two X chromosomes and becomes haemophilic only if both carry the recessive allele ($X^hX^h$); with one defective allele she is a normal carrier ($X^hX$).
A haemophilic female needs a haemophilic father and a carrier (or affected) mother, which is very rare.
So the disease is far more common in males because it is due to an X-linked recessive mutation.
A male has only one X chromosome (XY), so a single recessive allele ($X^hY$) is enough to make him haemophilic; there is no second allele to mask it.
A female has two X chromosomes and becomes haemophilic only if both carry the recessive allele ($X^hX^h$); with one defective allele she is a normal carrier ($X^hX$).
A haemophilic female needs a haemophilic father and a carrier (or affected) mother, which is very rare.
So the disease is far more common in males because it is due to an X-linked recessive mutation.