11.1 Fundamentals of Evolutionary Genetics

Genetic concepts and mechanisms form the foundation of evolutionary biology. From genes and alleles to natural selection and genetic diversity, these principles explain how organisms change over time and adapt to their environments.

Understanding Hardy-Weinberg equilibrium and its deviations is crucial for grasping population genetics. This theoretical model helps scientists analyze genetic variation and predict how allele frequencies might change in real-world populations.

Genetic Concepts and Mechanisms

Key terms in evolutionary genetics

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• Gene: DNA segment coding for specific protein or RNA molecule acts as hereditary unit passed from parent to offspring (insulin gene)
• Allele: Alternative form of gene at particular locus creates genetic variation within species (ABO blood type alleles)
• Genotype: Genetic makeup of organism determines combination of alleles for specific trait (Aa for heterozygous individual)
• Phenotype: Observable characteristics resulting from interaction between genotype and environment (eye color, height)

Principles of natural selection

• Variation: Differences in traits among individuals in population provide basis for selection (beak shapes in Galápagos finches)
• Inheritance: Genetic material transmission from parents to offspring enables trait heritability (eye color inheritance)
• Differential reproduction: Varying success in survival and reproduction among individuals determines fitness (antibiotic resistance in bacteria)
• Adaptation: Accumulation of beneficial traits over generations increases frequency of advantageous alleles (camouflage in peppered moths)

Factors shaping genetic diversity

• Genetic drift: Random changes in allele frequencies in small populations alter genetic makeup (founder effect in Amish populations)
• Gene flow: Transfer of genetic variation between populations through migration and interbreeding (human population admixture)
• Mutation: DNA sequence changes introduce new genetic variation
  • Point mutations: Single nucleotide changes
  • Insertions/deletions: Addition or removal of DNA segments
  • Chromosomal mutations: Large-scale structural changes

Hardy-Weinberg equilibrium and deviations

• Hardy-Weinberg equilibrium: Theoretical state where allele frequencies remain constant across generations assumes large population, random mating, no selection, mutation, or migration
• Hardy-Weinberg equation: $p^2 + 2pq + q^2 = 1$ calculates expected genotype frequencies
• Deviations from Hardy-Weinberg equilibrium:
  • Non-random mating: Assortative mating based on phenotype
  • Selection pressures: Natural or artificial selection favoring certain alleles
  • Genetic drift: Significant in small populations
  • Mutations: Introduction of new alleles
  • Gene flow: Migration between populations