4.3.6

Mutations, Genetic Drift, & Gene Flow

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Genetic Drift, Mutations, & Gene Flow

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

Genetic drift & mutations

Genetic drift & mutations

  • 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.
Small populations

Small populations

  • 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.
Genetic bottlenecks

Genetic bottlenecks

  • 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.
Founder effects

Founder effects

  • 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.
Founder effect - example

Founder effect - example

  • 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

Gene flow

  • 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.
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1

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Unity & Diversity - Ecosystems

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Practice questions on Mutations, Genetic Drift, & Gene Flow

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    What factor causes genetic drift to have a larger influence on evolutionary change?Multiple choice
  2. 2
    Which of the following statements about genetic drift are true?True / false
  3. 3
    What is the name for a sudden decrease in genetic diversity of a population, often caused by environmental factors?Multiple choice
  4. 4
    What is the name for a sudden decrease in genetic diversity of a population, often caused by environmental factors?Multiple choice
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