Final answer:
The founder effect is the reduced genetic diversity seen when a population descends from a small number of ancestors, specifically due to genetic drift in a new population established from a larger one.
Step-by-step explanation:
The reduced genetic diversity which occurs when a population is descended from a small number of colonizing ancestors is known as the founder effect. This is a magnification of genetic drift that takes place when members of a larger population migrate to establish a new population, carrying with them an unrepresentative set of alleles.
It occurs when a small group of individuals migrates away from a larger population and establishes their own population. The genetic structure of the new population will match that of the founding group, leading to reduced diversity.
The classic example of the founder effect is the genetic history of the Afrikaner population of Dutch settlers in South Africa. This population exhibits unusually high incidences of Huntington's disease (HD) and Fanconi anemia (FA), which is attributed to a higher-than-normal proportion of the founding colonists carrying certain mutations.
The founder effect contrasts with the bottleneck effect, which occurs when there is a significant reduction in population size due to events such as natural disasters, leading to a sudden reduction in genetic variability.