Random genetic drift in a population probably result from :
Genetic drift is when a small group of individuals leave a large population and establish a new one in a geographically isolated region. so when the gene distribution in a small populations evolves randomly, we call that phenomenon - genetic drift.
Let me give you an example, In a population, mice with black fur outnumber the mice with white fur 9 to 1 in the large population. As a result of a natural disaster, say two mice - one black and one white, escape on a log to another isolated island. The ratio of black mice to white in the isolated population will mostly not follow the same trend as the mainland population. As you can see, in the new population the ratio of black mice to the white mice is half and half. As the mice reproduce, they no longer follow the distribution of the main population. This is an example of genetic drift in action is called the founder effect.