7.4 Population genetics - mutation, gene flow and genetic drift

Population Genetics

  • Definition: Population genetics is the study of how a population changes over time, leading to evolution.

  • Key concepts:

    • Genetic Diversity: Result of mutations and individual movement (gene flow).

    • Alleles: Variants of a gene that contribute to diversity.

    • Polygenic Traits: Traits influenced by multiple genes (e.g., height in humans).

Genetic Variability

  • New alleles introduced through:

    • Mutation:

      • Major source of genetic variation.

      • Affects phenotypes and is the basis for natural selection.

    • Gene Flow: Movement of individuals between populations.

Phenotypic Distribution

  • Graphical Representation: Height distribution among individuals can be represented as:

    • Bell-shaped curve (normal distribution) showing continuous data.

    • Most individuals cluster around the average height.

Role of Mutations

  • Types of mutations and their effects:

    • Beneficial Mutations: Rare, increase in frequency due to natural selection.

    • Neutral Mutations: Persist in populations; can provide potential future advantages.

    • Detrimental Mutations: Most are quickly eliminated.

    • Lethal Mutations: Significant negative impact on survival.

Factors Influencing Allele Frequency

  • Natural Selection: Primary driver of evolution; alleles conferring advantages are more likely to be passed on.

  • Genetic Drift: Random changes in allele frequency due to chance events (e.g., natural disasters).

  • Gene Flow: Introduction of new alleles via immigration or potential loss via emigration.

  • Selective Pressures: Environmental factors selecting for traits suited to survival.

  • Sexual Selection: Non-random mating leads to allele frequency changes.

Historical Context

  • Key Contributors:

    • Mendel:

      • Established foundational principles of genetic inheritance.

    • Darwin:

      • Introduced the concept of natural selection as a mechanism for evolution.

Models of Change

  • Mathematically-based models predict genetic shifts under various selective pressures:

    • Contributions from Mendel's and Darwin's research.

Genetic Similarity

  • Human Genetic Composition:

    • 99.9% genetic similarity among humans, with variations due to small differences.

    • Relationship to other species: 99% shared with chimpanzees and 60% with chickens.

  • Implications of SNPs:

    • Analysis of single nucleotide polymorphisms helps trace variations affecting traits and health outcomes.

Genetic Stability and Change

  • Fitness and Reproductive Capacity: Changes in allele frequencies occur based on reproductive success.

  • Outcomes of changes:

    • Increased fitness leads to higher allele frequencies.

    • Alleles associated with increased vulnerability decrease in frequency.