$\bullet$ Change in gene frequency in a small population by chance is known as genetic drift. Genetic drift has two ramifications, one i bottle neck effect and another is founder's effect.

$\bullet$ When accidentally a few individuals are dispersed and act as founders of a new isolated population, founder's effect is said to be observed.

$\bullet$ Crossing over which occurs during gamete formation results in genetic recombination.

$\bullet$ Mutations are random and directionless.