A pleiotropic gene:

Options

A. Controls multiple traits in an individual.
B. Is expressed only in primitive plants.
C. Is gene evolved during Pliocene
D. Controls a trait only in combination with another gene

Answer

### Step-by-Step Text Solution:

1. **Understanding Pleiotropic Genes**:
A pleiotropic gene is defined as a single gene that influences multiple phenotypic traits. This means that one gene can affect various characteristics in an organism.

2. **Distinguishing from Other Genetic Concepts**:
It is important to differentiate pleiotropy from polygenic inheritance. In polygenic inheritance, multiple genes contribute to a single trait, while in pleiotropy, one gene affects multiple traits.

3. **Examples of Pleiotropic Genes**:
A classic example of a pleiotropic gene in humans is the gene responsible for phenylketonuria (PKU). This gene encodes the enzyme phenylalanine hydroxylase, which is crucial for metabolizing the amino acid phenylalanine.

4. **Effects of Pleiotropic Genes**:
The deficiency of the enzyme due to mutations in the PKU gene leads to several health issues, including:
- Mental retardation
- Eczema (skin inflammation)
- Lighter skin pigmentation

5. **Evaluating the Options**:
- **Option A**: "Control multiple traits in an individual" - This is correct as it describes the nature of pleiotropic genes.
- **Option B**: "Expressed only in primitive plants" - This is incorrect since pleiotropic genes are found in various organisms, including humans.
- **Option C**: "Is gene involved during Pliocene" - This is incorrect as it misrepresents the evolutionary context of pleiotropic genes.
- **Option D**: "Controls a trait only in combination with another gene" - This is incorrect because pleiotropic genes can control multiple traits independently.

6. **Conclusion**:
The correct answer to the question is that a pleiotropic gene controls multiple traits in an individual.