Final answer:
Genetic drift often results in decreased genetic variability within a population, particularly when events like natural disasters cause both the bottleneck and founder effects, which reduce diversity and the population's ability to adapt.
Step-by-step explanation:
Following a drift event, such as a natural disaster or the founder effect, the genetic variability in a population will often decrease. This is because genetic drift is influenced by random chance, which can lead to certain alleles being overrepresented or completely lost in a population.
The example of the Afrikaner population of Dutch settlers in South Africa illustrates the founder effect, where a high proportion of the founding colonists carried certain mutations, resulting in unusually high incidences of genetic disorders such as Huntington's disease and Fanconi anemia.
The bottleneck effect can also occur following a disaster that kills a large portion of the population non-selectively, causing a sharp reduction in genetic variation and leaving the genetic structure of the survivors as representative of the entire population.
Small and isolated populations are particularly susceptible to genetic drift. Events that drastically reduce the population's size, such as natural disasters, can magnify the effects of genetic drift. These events can sometimes lead to a population that is genetically very different from the pre-disaster population. Over time, genetic drift can completely eliminate certain alleles from a group of organisms, potentially leading to a loss of diversity and adaptability.