Which of the following best compares the effects of genetic drift and gene flow on the genetic makeup of a population? they are both random processes, but genetic drift decreases genetic variation and gene flow increases it. they are both selective processes, but genetic drift increases genetic variation and gene flow decreases it. they both decrease genetic variation, but gene flow is random and genetic drift is not. they both increase genetic variation, but gene flow is selective and genetic drift is not.

The correct answer is first, they are both random processes, but genetic drift decreases genetic variation and gene flow increases it.

Explanation:

Genetic drift and genetic variation are both random process and two of the forces of evolution. Genetic drift is the change in the allele frequency and also called allelic drift which is mostly seen in a small population.  

In a small population, due to random sampling, some alleles can be lost because of small allelic frequency present in a small population. This leads to a decrease in the genetic variation among the population.

Gene flow is the flow of genes or alleles from a population present in an area to another population present in another location. This increases genetic variation because it leads to the migration of different alleles in a new population.