<u><em>Genetic variation</em></u> occurs because beneficial traits exist in a collection of genes, and <u><em>gene flow</em></u> makes these traits more prevalent in populations.
Explanation:
In biology, genetic variation can be described as the different genotypes which occur in species of the same kind. This genetic variation allows those organisms to survive on Earth which are better adapted to survive to the environmental changes.
The organisms which are better adapted to live in an environment will reproduce and pass their traits to the offsprings. Over time, these traits will become more prevalent in a population.
