The Afrikaners are an example of a founder effect that occurs when population and the random decrease in genetic variation is an example of genetic drift.
Explanation:
When some individuals from a population move to form a new colony, this phenomenon is called founder effect as in case of Afrikaners. The small population or group of individuals forming a new colony may not exhibit the full genetic diversity of the population they were once the part.
The alleles would get expressed in different frequencies than it would have in original population.
There are chances that some alleles are lost or missing also. The new colony formed has small population so chances of genetic drift are very strong.
Genetic drift does not depend upon the benefit or harmful effect of the alleles as it occurs merely by chance sampling. The small population of Afrikaners felt the effect of genetic variation hence strong genetic drift is seen in them.