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 the options provided in the context of Down syndrome, which is caused by this genetic condition.

### Step-by-Step Solution:

1. **Understanding Trisomy 21**:
- Trisomy 21, also known as Down syndrome, is a genetic 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.

2. **Evaluating the Options**:
- **Option A: Psychomotor and mental development is retarded**:
- This is true. Individuals with Down syndrome often experience delays in psychomotor skills and mental development due to the extra genetic material affecting brain development.

- **Option B: Mental retardation**:
- This is also true. Mental retardation (now more commonly referred to as intellectual disability) is a significant characteristic of Down syndrome, with varying degrees of severity.

- **Option C: Presence of gynaecomastia**:
- This is false. Gynaecomastia (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 of Down syndrome.

3. **Conclusion**:
- The correct characters associated with trisomy 21 (Down syndrome) are A and B. Therefore, the correct answer to the question is that individuals with trisomy 21 exhibit psychomotor and mental development retardation, as well as mental retardation.

### Final Answer:
The correct options are A and B.