Occasionally, a single gene may express more than one effect. The phenomenon is called

Options

A. multiple allelism
B. mosaicism
C. pleiotropy
D. polygeny

Explanation

**Step-by-Step Text Solution:**

1. **Understanding the Question**: The question asks about a phenomenon where a single gene expresses more than one effect. This is a key concept in genetics.

2. **Identifying the Phenomenon**: The phenomenon where a single gene influences multiple traits is known as **pleiotropy**.

3. **Explaining Pleiotropy**: Pleiotropy occurs when one gene affects multiple phenotypic traits. This means that a mutation in a single gene can lead to changes in several characteristics of an organism.

4. **Providing Examples**:
- **Example 1**: In *Drosophila* (fruit flies), a gene responsible for white eye color also affects the shape of the male reproductive organ and sperm storage. This illustrates how one gene can control multiple traits.
- **Example 2**: Sickle cell anemia is another example of pleiotropy. The mutation in the hemoglobin gene causes red blood cells to become sickle-shaped, leading to various health issues such as pain, anemia, and increased risk of infections. This demonstrates how one genetic change can have widespread effects on an individual's health.

5. **Conclusion**: Therefore, the phenomenon where a single gene expresses more than one effect is called **pleiotropy**.

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