One of the following is called Sewall Wright effect `:`

Options

A. The movement of individual from one place to another
B. The random changes in gene frequencies in a population occurring by chance
C. The change in biological properties of individuals which prevent interbreeding of naturally sympatirc population
D. Change in gene structure and expression due to deletion and addition of nucleotides

Answer

To solve the question regarding the Sewall Wright effect, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks which of the given options is referred to as the Sewall Wright effect.

2. **Review the Options**: The options provided are:
- A) The movement of individuals from one place to another
- B) The random change in the gene frequency in a population occurring by chance
- C) The change in the biological property of individuals which prevents integration of natural sympatric populations
- D) Change in gene structure and expression due to methylation and addition of nucleotides

3. **Define the Sewall Wright Effect**: The Sewall Wright effect, also known as genetic drift, refers to the random changes in allele frequencies that occur in small populations due to chance events. This effect is more pronounced in smaller populations where random events can have a larger impact on the overall genetic makeup.

4. **Analyze Each Option**:
- **Option A**: This describes migration, which is not related to the Sewall Wright effect.
- **Option B**: This describes random changes in gene frequency due to chance, which aligns with the definition of the Sewall Wright effect.
- **Option C**: This refers to reproductive isolation and does not pertain to the Sewall Wright effect.
- **Option D**: This discusses changes in gene structure, which is not the focus of the Sewall Wright effect.

5. **Select the Correct Answer**: Based on the definitions and analysis, the correct answer is **Option B**: The random change in the gene frequency in a population occurring by chance.

### Final Answer:
The Sewall Wright effect is referred to as **the random change in the gene frequency in a population occurring by chance** (Option B).

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