The factor that leads to Founder effect in a population is :

The correct answer is Genetic drift.

Step 1: Understand the founder effect.

The founder effect occurs when a new population is established by a very small number of individuals taken from a larger original population. Because only a few individuals contribute their genes, the allele frequencies in the new population can differ dramatically from those in the original group.

Step 2: Identify the mechanism that causes this change.

The change in allele frequencies is due to random sampling of alleles from the original gene pool. This random sampling is a hallmark of genetic drift, which describes stochastic changes in allele frequencies that are especially pronounced in small populations.

Step 3: Contrast with other factors.

‑ Mutation introduces new alleles, but does not by itself cause the dramatic shift in existing allele frequencies seen in the founder effect.
‑ Natural selection changes allele frequencies based on differential reproductive success, which is a directional, non‑random process.
‑ Genetic recombination reshuffles alleles within individuals but does not alter overall allele frequencies across generations.

Step 4: Conclude.

Since the founder effect is driven by the random fixation or loss of alleles when a small group forms a new population, the underlying factor is genetic drift.