The random change in allele frequencies is called . Genetic drift can lead to the fixation of an and occurs rapidly in populations. When populations are reduced following a major disaster the resulting random change in allele frequencies is called the . If the population returns to its pre-disturbance size, genetic variation is generally than in the original population.

1. Genetic drift

2. allele

3. small

4. Bottleneck effect

4. Lower

Explanation:

1. Genetic drift refers to the random or uncontrolled process which changes the allele frequency and becomes one of the evolutionary force like a natural catastrophe.

2. This lead to the fixation of the allele in the population as the selected population with allele survive.

3. The process of genetic drift is observed in the small population as the small population is easily affected by the natural catastrophe.  

4. Bottleneck effect is observed when the large portion of the population is eliminated and the surviving allele of the living population is passed on to the generation.

5. If the population returns to its pre-disturbed state then the genetic variation is lower in the population as compared to the original population because the population genetic drift eliminates the allele and changes frequency.

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