Genetic drift in a population affects the gene pool in which of the following ways?

Genetic Drift is a term used to describe part of the evolutionary process. Genetic Drift is a term describing the random environmental factors such as volcanic eruptions, trees falling down, forest fires etc, that affect the gene frequency in the population of a species after the event has taken place. So, we can say that genetic drift in a population can affect the gene pool by either allowing the gene pool to increase of decrease. A typical example is that of the worldwide rhino population. The more the rhinos are poached, the smaller the genetic pool becomes. Eventually this can lead to the extinction of the species. 

He used pea plants to study the patterns of heredity.