Question

Haemophilia is more commonly seen in human males than in human females because

• A. A greater proportion of girls die in infancy
• B. This disease is due to an Y-linked recessive mutation
• C. This disease is due to an X-linked recessive mutation
• D. This disease is due to an X-linked dominant mutation

Answer 1

Answer: (C)

This disease is due to an X-linked recessive mutation

Answer 2

The correct answer is C:This disease is due to an X-linked recessive mutation
Haemophilia is a sex linked disease in which the patient continues to bleed even from a minor cut since he or she does not possess the natural phenomenon of blood clotting. Haemophilia (= hemophHia) is genetically due to the presence of a recessive gene h, carried by Y-chromosome. A female becomes haemophiliac only when both its X- chromosomes carry the gene (XhXh). However, such females generally die before birth because the combination of these two recessive alleles is lethal. A female having only one allele for haemophilia (XXh) appears normal because the allele for normal blood clotting present on the other X-chromosome is dominant. Such females are known as carriers. In case of males, a single gene for the defect is able to express itself as theY-chromosome is devoid of any corresponding allele (XhY) in which an organism has three times (3n) the haploid number (n) of chromosomes.