Question

Pick out the incorrect statement for the diseases given:

• A. Down’s syndrome is due to aneuploidy
• B. Haemophilia is a sex ­linked recessive disease
• C. Sickle cell anemia is an X-­linked recessive gene disorder
• D. Phenylketonuria is an autosomal recessive gene disorder

Answer 1

The correct option is C

Sickle cell anemia is an X-­linked recessive gene disorder

The correct option is C.

Explanation of the correct option:

1. Sickle cell anemia is an autosomal recessive disorder.
2. Sickle cell anemia is caused due to the substitution of glutamic acid with valine at the 6th position of the beta-globin chain of haemoglobin.
3. The gene for the beta-globin chain is present on chromosome 11.

Explanation of the incorrect options:

Option A:

1. Aneuploidy occurs when members of a pair of homologous chromosome fail to segregate during meiosis.
2. It leads to the loss or gain of one or more chromosomes.
3. Down's syndrome occurs due to the presence of an additional copy of chromosome 21.

Option B:

1. Haemophilia is a sex linked recessive disorder.
2. The gene for it is present on the X chromosome.
3. An unaffected carrier female passes it onto some of her male offspring.

Option D:

1. Phenylketonuria is an autosomal recessive gene disorder.
2. It is an example of pleiotropy.
3. It is caused by a mutation in the gene coding for the enzyme phenylalanine hydroxylase.

Final answer: The incorrect statement is ‘Sickle cell anemia is an X-­linked recessive gene disorder’.