If change in gene frequencies in a population occurs by chance, then it is called as:

Options

A. (1) Natural selection
B. (2) Gene flow
C. (3) Gene migration
D. (4) Genetic drift

Answer

To solve the question "If change in gene frequencies in a population occurs by chance, then it is called as:", we can follow these steps:

### Step-by-Step Solution:

1. **Understand Gene Frequencies**: Gene frequencies refer to how often a particular gene variant (allele) appears in a population. These frequencies can change over time due to various factors.

**Hint**: Think about what influences the distribution of genes in a population over generations.

2. **Identify the Concept of Chance**: The question specifies that the change in gene frequencies occurs "by chance." This indicates that we are looking for a process that is random rather than driven by natural selection or other deterministic factors.

**Hint**: Consider processes that lead to random changes in allele frequencies without any selective pressure.

3. **Recall Relevant Biological Principles**: The Hardy-Weinberg principle states that gene frequencies in a population remain constant in the absence of evolutionary influences. However, certain factors can disrupt this equilibrium.

**Hint**: Reflect on the factors that can lead to deviations from the Hardy-Weinberg equilibrium.

4. **Identify the Correct Term**: The term that describes a change in gene frequencies due to random sampling effects (chance) is "genetic drift." This phenomenon occurs especially in small populations where random events can lead to significant changes in allele frequencies.

**Hint**: Think about how random events can disproportionately affect small groups compared to larger populations.

5. **Eliminate Incorrect Options**:
- **Natural Selection**: This process is not random; it involves differential survival and reproduction based on advantageous traits.
- **Gene Flow**: This refers to the movement of alleles between populations, which is also not a chance event.
- **Gene Migration**: Similar to gene flow, this involves the movement of individuals and their alleles from one population to another, not random chance.

**Hint**: Consider the definitions of the other terms and how they relate to the concept of chance.

6. **Conclusion**: The correct answer is "genetic drift," as it specifically refers to changes in gene frequencies that occur by chance.

### Final Answer:
The change in gene frequencies in a population that occurs by chance is called **genetic drift**.

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