Question

In humans, Down syndrome is caused by

• A. Trisomy 16
• B. Trisomy 18
• C. Trisomy 21
• D. Trisomy 22

Hint:

Remember: Down syndrome = Trisomy 21, Edwards syndrome = Trisomy 18, Patau syndrome = Trisomy 13.

Answer 1

The Correct Option is C

Step 1: Definition.
Down syndrome is a genetic disorder caused by an extra copy of chromosome 21 (also called trisomy 21).
Step 2: Exclude other options.
- Option (A) Trisomy 16: Causes miscarriage, not Down syndrome.
- Option (B) Trisomy 18: Causes Edwards syndrome.
- Option (C) Trisomy 21: Correct – leads to Down syndrome.
- Option (D) Trisomy 22: Causes severe abnormalities but not Down syndrome.
Step 3: Clinical features.
Common features of Down syndrome include intellectual disability, characteristic facial features, and congenital heart defects.
Final Answer: \[ \boxed{\text{Down syndrome is caused by Trisomy 21.}} \]