9C: Genetic Drift and Gene Flow

Gene Flow

• The introduction or removal of alleles from a population due to migration or interbreeding of individuals between populations

Migration

Migration can happen when population are in close proximity or when a barrier between populations is removed:

• Immigration

• Emigration

Immigration

Where individuals move into a population

Emigration

Where individuals move out of a population

Effects of Gene Flow on Genetic Diversity

Gene flow can increase or decrease genetic diversity

• Immigration

  • Can increase genetic diversity as new alleles may be added to the population

• Emigration

  • Can decrease genetic diversity as alleles may be removed from the population

• Interbreeding

  • Can increase genetic diversity as new alleles may be added to the population

  • It will also decrease genetic diversity between populations (populations become more similar)

Genetic Drift

• The change in allele frequency due to a random chance event that has a dramatic effect on the population’s gene pool

• Causes a decrease in genetic diversity

• May occur through either

  • The bottleneck effect

  • The founder effect

The Bottleneck Effect

• A reduction in genetic diversity that occurs when a large proportion of a population is removed by a random event (natural disaster or human intervention)

• Genetic diversity decreases because alleles are removed from the gene pool

Effects of bottleneck effect

• Only a small number of individuals remain in the gene pool to contribute their genes to the next generation

• The small sample that survives will not be representative of the original larger gene pool

• The small surviving population is often affected by inbreeding

The Founder Effect

• When the reduction in genetic diversity that occurs when a new population is started by a small unrepresentative sample of the original population

• Genetic diversity is reduced in the new population due to their small gene pool

Problems With Reduced Genetic Diversity

Reductions in genetic diversity can lead to:

• Inbreeding

• Lower adaptive potential

How Does Inbreeding Lower Genetic Diversity

It keeps harmful alleles in the gene pool

How Does Lower Adaptive Potential Lower Genetic Diversity

Populations become renewable to new selection pressures that could challenge and potentially wipe out the entire population due to the absence of advantages alleles

Inbreeding

• The production of offspring from parents that are closely related or genetically similar

• This may be unavoidable in small populations of individuals that are genetically similar

• Results in an increase of homozygous individuals in a population and for the loss of genetic diversity