Founder's effect is best illustrated by which scenario?

• A. A small group splits from a larger population, reducing genetic diversity.
• B. A large population experiences natural selection, increasing diversity.
• C. A population experiences a random mutation that benefits many individuals.
• D. Two populations mate and share all genetic variants equally.

Answer: (A)

The key idea is how a very small number of individuals starting a new population can alter the genetic makeup. The founder effect occurs when a tiny group separates from a larger population to form a new community. Because the new population is founded by only a few individuals, its gene pool is just a sample of the original diversity, not a full reflection. This sampling can dramatically change allele frequencies and reduce overall genetic diversity in the new population, simply by chance. That’s exactly what happens when a small group splits off from a larger population.

The other scenarios don’t capture this situation. A large population undergoing natural selection changes allele frequencies due to selective pressures but isn’t started by a small founder group, so it doesn’t illustrate the founder effect. A random beneficial mutation changes frequencies of a single allele rather than creating a new population from a tiny founding gene pool. Two populations mating and sharing all genetic variants equally describes gene flow that tends to homogenize populations, not produce the distinct founder-driven shift seen when a few founders start a new population.