Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: Bottleneck effect occurs when a population suddenly gets much smaller. This might happen because of a natural disaster such as a forest fire. By chance, allele frequencies of the survivors may be different from those of the original population. Answer: bottleneck effect
Output:
What effect occurs when a population suddenly gets much smaller, due to natural disaster or other cause?