A pleiotropic gene

Options

A. is expressed only in primitive plants
B. is a gene evolved during pliocene
C. controls a trait only in combination with another gene
D. controls multiple traits in an individuals

Answer

### Step-by-Step Solution:

1. **Understanding Pleiotropy**:
- A pleiotropic gene is a single gene that influences multiple phenotypic traits. This means that one gene can have effects on different characteristics of an organism.

2. **Analyzing the Options**:
- The question provides four statements about a pleiotropic gene. We need to evaluate each statement to determine which one correctly describes the nature of pleiotropy.

3. **Evaluating Each Statement**:
- **Option 1**: "A pleiotropic gene is expressed only in the primitive plant."
- This statement is incorrect because pleiotropic genes can be found in various organisms, not just primitive plants.

- **Option 2**: "A gene evolved during the Pleiocene."
- This statement is also incorrect as pleiotropy is a genetic concept and is not limited to a specific evolutionary period.

- **Option 3**: "Controls a trait only in combination with another gene."
- This statement describes epistasis rather than pleiotropy. Pleiotropic genes can affect traits independently.

- **Option 4**: "Controls multiple traits in an individual."
- This statement accurately describes a pleiotropic gene, as it indicates that one gene can influence several traits.

4. **Conclusion**:
- Based on the evaluations, the correct answer is **Option 4**: "Controls multiple traits in an individual."

5. **Example of Pleiotropy**:
- A common example of a pleiotropic gene is the gene responsible for phenylketonuria (PKU). This gene affects multiple traits, such as mental retardation and skin pigmentation, due to the absence of the enzyme phenylalanine hydroxylase, which is crucial for converting phenylalanine to tyrosine.