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

Concept:

• The founder effect occurs when a small population gets drifted from the parent population and becomes a new population.
• Allele frequency changes as compared to their parent population and thus forming a new population with a new genotype.

Explanation:

• Option 1: Genetic drift is the change in allele frequencies that occurs by chance. It occurs in a small population. The founder effect is a result of genetic drift.
• Option 2: Natural selection is a process by which the organism more fitted to the environment will survive and reproduce to form more of its kind. They are more adapted to their environment.
• Option 3: Genetic recombination is the process of the exchange of DNA fragments between two different chromosomes leading to variation.
• Option 4: Mutation is the change in DNA sequence due to errors in DNA replication, any exposure to mutagens, etc.

So, the correct answer is option 1.