Select the correct statements.
I. Haemophilia is a sex-linked recessive character.
II. Down’s syndrome is due to aneuploidy.
III. Phenylketonuria is an autosomal dominant gene disorder.
IV. Sex complement of a Klinefelter’s syndrome is XXY.
V. Sickle cell anaemia is an X-linked recessive gene disorder.

The correct option is A I, II, and IV are correct.

• Haemophilia is a sex-linked or X-linked recessive disorder.
• Down’s syndrome is due to trisomy of 21st chromosome, which is an aneuploidy.
• Phenylketonuria is an autosomal recessive disorder.
• Sex complement of Klinefelter’s syndrome is XXY (47, XXY), so it is also referred to as allosomal trisomy. It only affects the male.
• Sickle cell anaemia is an autosomal recessive disorder. It is due to single base mutation with the replacement of thymine to adenine in the 6th position of the amino acid. The change causes the substitution of the 6th amino acid glutamic acid to valine, causing the haemoglobin to become sickle shaped.