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

The correct option is Genetic drift.

Step-by-Step Explanation:

1. Understanding Genetic Drift:
Genetic drift refers to random fluctuations in the allele frequencies within a population over generations, occurring purely by chance. Unlike natural selection, genetic drift does not select for traits that are advantageous; instead, changes in the gene pool occur randomly. The impact of genetic drift is significantly stronger in small populations.

2. What is the Founder Effect?
The Founder effect is a classic example of genetic drift. It happens when a small group of individuals breaks away from a larger parent population to colonize a new, isolated habitat. Because the starting group is so small, the alleles they carry represent only a tiny, random sample of the genetic diversity present in the original population. As a result, the new population's genetic makeup can look very different from the original population purely by random chance.

3. Conclusion:
Since the Founder effect is caused by the random sampling of a small number of colonizing individuals, the underlying evolutionary mechanism is genetic drift.

4. Why the other options are incorrect:
- Natural selection: This is a non-random process where environmental pressures select for traits that aid survival and reproduction.
- Genetic recombination: This occurs during sexual reproduction (crossing over) to create new combinations of existing alleles, but it does not cause the drastic, random loss of alleles associated with forming a new colony.
- Mutation: This is the source of brand-new alleles through changes in DNA, whereas the Founder effect changes the frequencies of already existing alleles due to isolation.