Natural selection favours those allels which make the organisms better adapted to the environment. Under which condition the two alternative alleles make an organism equally well adapted?

Options

A. Genetic drift
B. In absence of predator
C. mutation
D. Bottle neck effect

Answer

To determine under which condition two alternative alleles make an organism equally well adapted to its environment, we can analyze the options provided in the question.

### Step-by-Step Solution:

1. **Understanding Natural Selection**: Natural selection is the process through which certain alleles become more common in a population because they confer a survival advantage in a given environment. This means that alleles that help organisms adapt better to their environment are favored.

2. **Evaluating Genetic Drift**: The first option is genetic drift. Genetic drift refers to random changes in allele frequencies in a population, which are not due to natural selection. Since the question specifically asks about natural selection, this option is not relevant. Therefore, it is incorrect.

3. **Considering Absence of Predators**: The second option discusses the absence of predators. In an environment without predators, there is no selective pressure on the organisms. This means that both alleles can persist in the population without one being favored over the other. Consequently, both alleles would lead to organisms that are equally well adapted, making this option correct.

4. **Analyzing Mutation**: The third option is mutation. Mutations introduce new alleles into a population but do not directly relate to the condition of being equally well adapted. Since mutations can lead to either beneficial, neutral, or harmful effects, this option does not satisfy the condition of equal adaptation and is therefore incorrect.

5. **Reviewing the Bottleneck Effect**: The fourth option is the bottleneck effect, which is a form of genetic drift that occurs when a population's size is significantly reduced. This does not relate to natural selection favoring alleles for adaptation, so this option is also incorrect.

6. **Conclusion**: The only condition under which two alternative alleles make an organism equally well adapted is in the absence of predators. Thus, the correct answer is that both alleles are equally well adapted when there are no predators present.

### Final Answer:
The two alternative alleles make an organism equally well adapted in the absence of predators.