Question

Pick out the correct statements.

I. Haemophilia is a sex linked recessive disease.
II. Inheritance pattern of haemophilia is the same as that of color blindness.
III. Phenylketonuria is an autosomal recessive gene disorder.
IV. Sickle cell anaemia is an X-linked recessive gene disorder.

• A. I, III, and IV are correct
• B. I, II, and III are correct
• C. I and IV are correct
• D. II and IV are correct

Answer 1

The correct option is B I, II, and III are correct

Haemophilia is a sex linked recessive disease. It is caused due to the presence of a mutant allele ‘h’ on the X chromosome in both males and females. For its expression in females, 2 identical recessive alleles have to be present on both the X chromosomes. In males, since there is only one X chromosome (the other being Y), presence of a single recessive allele is enough for the expression of the trait. Hence, it is a recessive trait.
Colour blindness is caused due to mutation of genes responsible for the production of cones (responsible for normal coloured vision in persons). These genes are located on the X chromosome. Its inheritance pattern is similar to that of haemophilia i.e., in an X linked recessive manner.
Phenylketonuria is an autosomal recessive disorder caused due to mutation in the gene coding for the enzyme phenylalanine hydroxylase located on chromosome number 12.
Sickle cell anaemia is caused due to mutation in the amino acid sequence of the beta globin chain of haemoglobin. The gene encoding the beta globin chain is located on chromosome number 11. Hence it is an autosomal disorder.
Hence, statements I, II, and III are correct and statement IV is incorrect.