Which of the following characters are seen in an individual with trisomy of chromosome number 21 ?
A. Psychomotor and mental development is retarded
B. Mental retardation
C. Presence of gynaecomastia
D. Loss of skin pigmentation

Options

A. Only A is correct
B. Only A & B are correct
C. Only A, B & C are correct
D. All are correct

Answer

To solve the question regarding the characters seen in an individual with trisomy of chromosome number 21, we need to analyze each option based on our knowledge of Down syndrome, which is caused by this chromosomal abnormality.

### Step-by-Step Solution:

1. **Understanding Trisomy 21**:
- Trisomy 21, also known as Down syndrome, occurs when there is an extra copy of chromosome 21, resulting in a total of 47 chromosomes instead of the usual 46.

2. **Analyzing Each Option**:
- **Option A: Psychomotor and mental development is retarded**:
- This is true. Individuals with Down syndrome often experience delays in psychomotor development and have difficulties in achieving developmental milestones.

- **Option B: Mental retardation**:
- This is also true. Mental retardation is a common characteristic of individuals with Down syndrome, with varying degrees of intellectual disability.

- **Option C: Presence of gynaecomastia**:
- This is false. Gynaecomastia, which is the development of breast tissue in males, is typically associated with Klinefelter syndrome (XXY), not Down syndrome.

- **Option D: Loss of skin pigmentation**:
- This is also false. Loss of skin pigmentation is not a characteristic associated with Down syndrome.

3. **Conclusion**:
- The correct options that describe characters seen in an individual with trisomy of chromosome number 21 are A and B. Therefore, the answer is A and B.

### Final Answer:
- **A. Psychomotor and mental development is retarded**
- **B. Mental retardation**