Down's syndrome is caused due to __________of chromosomes.

Options

A. autosomal addition
B. autosomal deletion
C. allosomal addition
D. allosomal deletion

Answer

**Step-by-Step Solution:**

1. **Understanding Down's Syndrome**: Down's syndrome is a genetic disorder characterized by a set of physical and intellectual disabilities. It is important to identify the cause of this condition to answer the question correctly.

2. **Identifying the Cause**: The primary cause of Down's syndrome is an abnormality in chromosome number. Specifically, it is associated with an extra copy of chromosome 21.

3. **Terminology**: The condition caused by the presence of an extra chromosome is referred to as "Trisomy." In the case of Down's syndrome, it is specifically known as Trisomy 21, indicating that there are three copies of chromosome 21 instead of the usual two.

4. **Types of Chromosomal Changes**: The options provided in the question include:
- Autosomal addition
- Autosomal deletion
- Allosomal addition
- Allosomal deletion

5. **Choosing the Correct Option**: Since Down's syndrome is caused by the addition of an extra chromosome (specifically chromosome 21), the correct term to describe this phenomenon is "autosomal addition." This is because chromosome 21 is an autosome (non-sex chromosome).

6. **Final Answer**: Therefore, Down's syndrome is caused due to **autosomal addition** of chromosomes.

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