Question

The trisomy for ${21}^{st}$ chromosome is called as

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

Answer 1

The correct option is A Down's syndrome

Presence of one chromosome in triplicate (2n+1) is called as trisomy. Trisomy of the 21 st chromosome causes Down's syndrome (45+XY/45+XX). It is characterized by round face, broad fore head and palmer crease with low intelligence. This makes option A correct.

Fertilization of an XX egg by a normal Y-bearing sperm results in 44+XXY chromosomes that cause Klinefelter syndrome. The affected males are feminine and carry few feminine characters. Option D is incorrect.

Turner's syndrome is caused by monosomy of X chromosome and is represented as 44 +XO; the individual are sterile females as they lack one X-chromosome. Option B is incorrect.

Option C is incorrect as sickle cell anemia is caused by point mutation in $H{b}^b$ gene, that codes the beta chain, while trisomy is chromosomal aberration.