11.3 Population Genetics and Hardy-Weinberg Equilibrium

Population genetics studies how genes behave in groups. It's all about tracking changes in allele frequencies over time. This topic dives into the Hardy-Weinberg principle, which sets a baseline for measuring genetic change in populations.

Factors like genetic drift, gene flow, and mutation can shake things up genetically. These forces drive evolution by altering allele frequencies in populations. Understanding these concepts helps explain how species adapt and change over time.

Genetic Composition of Populations

Gene Pools and Allele Frequencies

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• Gene pool represents the total genetic diversity within a population
• Consists of all alleles at all gene loci in a population
• Allele frequency quantifies the proportion of a specific allele at a gene locus in a population
• Calculated by dividing the number of copies of a specific allele by the total number of alleles at that locus in the population
• Allele frequencies can change over time due to various evolutionary forces (mutation, natural selection, genetic drift, gene flow)

Hardy-Weinberg Equilibrium and Principle

• Hardy-Weinberg equilibrium describes a population that is not evolving
• Occurs when allele and genotype frequencies remain constant from generation to generation
• Hardy-Weinberg principle states that allele and genotype frequencies in a population remain constant in the absence of evolutionary influences
• Assumes random mating, no mutation, no migration, no natural selection, and an infinitely large population size
• Provides a baseline for measuring evolutionary change in a population
• Deviations from Hardy-Weinberg equilibrium indicate that a population is evolving

Factors Affecting Allele Frequencies

Genetic Drift and Its Effects

• Genetic drift is a random change in allele frequencies due to chance events
• Occurs in small populations where sampling error can have a significant impact on allele frequencies
• Bottleneck effect is a form of genetic drift that occurs when a population undergoes a drastic reduction in size (natural disasters, habitat destruction)
• Leads to a loss of genetic diversity and can result in the fixation or loss of alleles
• Founder effect is another form of genetic drift that occurs when a small group of individuals establishes a new population (colonization of a new habitat)
• New population may have different allele frequencies compared to the original population

Gene Flow, Mutation, and Non-random Mating

• Gene flow is the transfer of alleles between populations through migration or interbreeding
• Can introduce new alleles into a population or change existing allele frequencies
• Mutation is a change in the DNA sequence that can create new alleles or modify existing ones
• Rare events but serve as the ultimate source of genetic variation in populations
• Non-random mating occurs when individuals mate with others based on specific traits or preferences (assortative mating, inbreeding)
• Can lead to changes in allele frequencies and genotype frequencies in a population