Genetic Drift & Founder Effect

Biology: Cambridge International A Level, topic 17.2.4

Genetic Drift, Mutations, & Gene Flow

Random events like mutations, genetic drift, and gene floe drive evolution and can change the genetics of a population.

By chance, some alleles are passed onto offspring and some are not.
This causes random changes in the allele frequencies in the population.
This affects the evolution of a population and is called genetic drift.
As mentioned previously, mutations are random changes in the sequence of DNA.
- Mutations are a source of new alleles, or new genetic variation, in any population.

Genetic drift tends to have a larger influence on evolutionary change in smaller populations.
This is because the gene pool (the sum of all the genes of a population) is smaller.
If the gene pool is smaller, any change in allele frequencies has a larger impact on the overall gene pool.

A population can go through a genetic bottleneck.
A genetic bottleneck is a sudden reduction in genetic variation in a population.
Bottlenecks can be caused by environmental factors like disease, flooding, drought, and famine.
A smaller gene pool means that genetic drift has more of an impact on these populations.

When a new population is founded, their genetic variation is only a subset of the original population.
Often, a population is founded by a small number of individuals, and their genetic variation is unlikely to be representative of the population that they came from.
Small numbers increase the impact of genetic drift in these populations.

The founder effect is believed to have been a key factor in the genetic history of the Afrikaner population of Dutch settlers in South Africa.
This is evidenced by mutations that are common in Afrikaners but rare in most other populations.
This is likely due to the fact that a higher-than-normal proportion of the founding colonists carried these mutations.
As a result, the population expresses unusually high incidences of Huntington’s disease (HD) and Fanconi anemia (FA).

Gene flow is the flow of alleles in and out of a population due to the migration of individuals or gametes.
While some populations are fairly stable, others experience more flux.
Many plants, for example, send their pollen far by wind to pollinate other populations of the same species some distance away.
This variable flow of individuals changes the gene structure of the population and can also introduce new genetic variation to populations in different locations.

What factor causes genetic drift to have a larger influence on evolutionary change?
Which of the following statements about genetic drift are true?
What is the name for a sudden decrease in genetic diversity of a population, often caused by environmental factors?
What is the name for a sudden decrease in genetic diversity of a population, often caused by environmental factors?