Principles of Inheritance and Variation · Question 166

Mongolian idiots are due to trisomy in 21st chromosome is called:

1. Klinefelter's syndrome
2. Down's syndrome
3. Turner's syndrome
4. Triplex syndrome

Answer

(2) Down's syndrome

Solution

As per NCERT, Down's syndrome is caused by the presence of an additional copy of chromosome number 21 (trisomy of 21).

The affected individual is short with a small round head, furrowed tongue, partially open mouth and retarded mental development (earlier called mongolism / mongolian idiocy).

Klinefelter's syndrome is 47, XXY and Turner's syndrome is 45, XO.

Answer: (2)