Question

Haemophilia is rare in women because

• A. It is a recessive autosomal disorder
• B. Women ought to be homozygous
• C. They have only one X chromosome
• D. They are more recessive to this

Answer 1

The correct option is B

Women ought to be homozygous

Haemophilia is a sex-linked recessive trait. The trait is associated with the X chromosomes.

Women are homozygous so they have XX chromosomes as sex chromosomes. They will exhibit the disease condition only if they are homozygous recessive i.e both the copies of the gene are defective. With just one defective copy (recessive allele), it gets masked by the good copy(dominant allele) and the women become carriers.

Males only have one X chromosome, they have no spare normal chromosome to override the chromosome which is defective.