Question

Daltonism haemophilia can occur in females due to

• A. Homozygous conditions in which both X chromosomes are altered at the same locus
• B. Heterozygous condition of X chromosome
• C. Homozygous condition of Y chromosomes
• D. None of the above

Answer 1

The correct option is A Homozygous conditions in which both X chromosomes are altered at the same locus

Daltonism haemophilia are X-linked recessive disorders. One copy of the affected gene in males in each cell is sufficient to cause the disorder. As we know that females have two copies of X-chromosomes as sex chromosomes, they need two copies of mutant allele to express the recessive trait. Females homozygous for the mutation i.e. with two copies of the affected gene, show the disorder. Females heterozygous for this trait are normal but serve as a carrier of the disease; this is because presence of wild type allele masks the expression of mutant allele in heterozygotes which makes option B incorrect. The disorders are X-linked, mutation in Y chromosome does not affect their inheritance; option C is wrong. Correct option is A.