What is Down's syndrome? Give its symptoms and cause. Why is it that the chances of having a child with Down's syndrome increases if the age of the mother exceeds forty years ?

Explanation

### Step-by-Step Text Solution

**Step 1: Definition of Down's Syndrome**
Down's syndrome, also known as Trisomy 21, is a chromosomal disorder caused by the presence of an extra copy of chromosome 21. This results in a total of three copies of this chromosome instead of the usual two.

**Step 2: Symptoms of Down's Syndrome**
Individuals with Down's syndrome may exhibit a range of symptoms, including:
- **Mental Retardation**: Cognitive impairment is common, with varying degrees of intellectual disability.
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