Question

A disease caused by an autosomal primary nondisjunction is

• A. Down's syndrome
• B. Klinefelter’s syndrome
• C. Turner’s syndrome
• D. Sickle cell anaemia

Answer 1

The correct option is A

Down's syndrome

The correct option is A.

Explanation of correct option:

1. Down syndrome is a genetic disorder that occurs due to trisomy 21.
2. In this condition, chromosome 21 (autosome) is repeated thrice rather than twice in a normal individual.
3. This condition arises due to the non-disjunction of chromosomes.
4. Non-disjunction refers to the inability of the sister chromatids to separate during cell division.

Explanation of incorrect option:

Option B:

1. Klinefelter’s syndrome is characterized by the presence of one extra ‘X’ chromosome in males.
2. It occurs when the ‘X’ chromosome fails to detach itself from the pair during meiosis.

Option C:

1. Turner’s syndrome arises when one ‘X’ chromosome is partially or completely missing in females.
2. It occurs due to an error during cell division.

Option D:

1. Sickle cell anemia is an autosomal recessive disorder that is characterized by sickle-shaped RBCs.
2. It is caused by a mutation in the β-globin gene located on chromosome 11.

Final answer

A disease caused by an autosomal primary nondisjunction is Down's syndrome.