Question

Which pair of the following diseases are caused by two genes located on human X chromosome?

• A. Colour blindness and phenylketonuria
• B. Colour blindness and haemophilia
• C. Colour blindness and albinism
• D. Colour blindness and hypertrichosis

Answer 1

The correct option is B Colour blindness and haemophilia

Albinism is a genetic defect of melanin production due to a mutation in a gene that encodes tyrosinase. Phenylketonuria (PKU) is an inborn metabolic error with impaired metabolism of phenylalanine due to the presence of the defective gene for phenylalanine hydroxylase. Albinism and Phenylketonuria are an autosomal disorder as their genes are present on autosomes, chromosome number 11 and 12 respectively; not on sex chromosomes. Hypertrichosis is sex-linked or autosomal disorder based on its type. Colour blindness and haemophilia are X-linked recessive disorders caused by a defect in gene present in X chromosome exclusively. Both are caused by the recessive allele on X chromosome. Thus, the correct answer is option B.