Drift and gene flow

Evolutionary Mechanisms

• Key Mechanisms: Understanding differences and similarities among the four evolutionary mechanisms.

• Allele Frequency Changes: Outcomes of each mechanism on allele frequencies.

• Genetic Drift: More prevalent in small populations due to sampling errors.

• Population Bottlenecks vs. Founder Effects: Key differences and similarities.

• Hardy-Weinberg Equilibrium: Evolutionary mechanisms lead to non-equilibrium genotype frequencies.

• Homogenizing Effect of Migration: Migration acts to equalize allele frequencies among populations.

Genetic Drift and Migration

Assumptions of Hardy-Weinberg (The Null Hypothesis)

• Random mating.

• No mutation.

• Infinitely large population.

• No genetic drift.

• No gene flow.

• No selection.

Consequences of Genetic Drift

• Possible outcomes include:

  • Reduction or increase in allele frequencies.

  • Introduction of new alleles.

• In terms of Hardy-Weinberg, genetic drift violates the assumption of infinite population size.

Causes of Genetic Drift

• Genetic drift is described as a sampling error where non-representative individuals survive and reproduce unevenly.

• More pronounced in smaller populations, where chance events can drastically change allele frequencies.

Loss of Diversity in Nature

• Drift and Loss of Allelic Diversity: Simulation studies show genetic drift leads to a loss of allelic diversity.

• Fate of Alleles: Any allele in a population will either be lost or become fixed (frequency of 1.0).

• Heterozygosity: Defined as the frequency of heterozygotes within a population, calculated using the formula H = p*q, where N is the population size.

Genetic Drift's Effect Over Time

• Eventually: Genetic drift tends to reduce genetic variation in a population over time.

• Population Bottleneck: A drastic reduction in the number of individuals leading to a decreased allelic diversity.

• Example: Pingelap Atoll and the consequences of a severe event causing a bottleneck effect.

Gene Flow

• Gene Flow Defintion: Migration of alleles between gene pools.

• Importance: Gene flow tends to homogenize allele frequencies between geographically separated populations, counteracting divergence.

• Significant in small populations where randomness can significatively influence genetic compositions.

• Wahlund Effect: Migration may lead to increased homozygosity, observable in population distributions.

Conservation Implications

• Inbreeding: Tends to increase in reduced populations leading to genetic issues.

• Studies: Introduction of Texas pumas into Florida panthers as a conservation mechanism.

Genetic Drift vs. Natural Selection

• Genetic Drift: Change due to chance sampling.

• Natural Selection: Change due to specific selection pressures.

• Founding events can lead to allele frequencies that may become homogenized if migration occurs between populations.

Conclusion

• Understanding the distinctions between genetic drift and gene flow, as well as their implications on conservation, is crucial for managing biodiversity and species at risk.