Question

In Down's Syndrome, there is :

• A. Extra "Chromosome 14"
• B. Extra "Chromosome 18"
• C. Extra "Chromosome 21"
• D. Extra "Chromosome X"

Hint:

A quick mnemonic for the most common viable autosomal trisomies:
Patau = Puberty (Age 13) = Trisomy 13.
Edwards = Election (Age 18) = Trisomy 18.
Down = Drinking (Age 21) = Trisomy 21.

Answer 1

The Correct Option is C

Step 1: Concept:
The question requires matching a well-known genetic disorder (Down Syndrome) to its specific chromosomal abnormality (aneuploidy).

Step 2: Step-by-step Explanation:

• Down's Syndrome is a genetic disorder caused by abnormal cell division during meiosis (non-disjunction), which results in an extra full or partial copy of a specific autosome.

• Medically, Down Syndrome is formally termed Trisomy 21, meaning the affected individual has three copies of Chromosome 21 instead of the usual two.

• For context regarding the other options:
- Trisomy 18 causes Edwards syndrome.
- Trisomy 13 causes Patau syndrome.
- Extra X chromosomes cause conditions like Klinefelter syndrome (XXY) or Triple X syndrome (XXX).

Step 3: Final Answer:
Down's Syndrome involves an extra Chromosome 21. This matches option (C).