The best example for pleiotropy is :-

Options

A. Skin colour
B. Phenylketoneuria
C. Colour Blindness
D. ABO Blood group

Answer

### Step-by-Step Solution:

1. **Understanding Pleiotropy**:
- Pleiotropy occurs when a single gene influences multiple phenotypic traits that seem unrelated. This means that one gene can have various effects on different characteristics of an organism.

2. **Identifying an Example**:
- To find the best example of pleiotropy, we need to look for a condition or trait where one gene affects multiple traits.

3. **Phenylketonuria (PKU)**:
- Phenylketonuria is a genetic disorder caused by a defect in the gene responsible for breaking down the amino acid phenylalanine. This defect is located on chromosome 12.

4. **Effects of PKU**:
- The accumulation of phenylalanine due to the defective gene leads to various phenotypic effects, including:
- Neurological issues (affecting nervous tissue)
- Skin and hair pigmentation changes (affecting integumentary tissues)
- These effects illustrate how one genetic defect can lead to multiple unrelated phenotypic traits.

5. **Conclusion**:
- Therefore, the best example of pleiotropy is **Phenylketonuria**, as it demonstrates how one gene can influence multiple, seemingly unrelated traits.