Population genetics explores how genetic variation changes within populations over time. It's the key to understanding microevolution, which happens when allele frequencies shift due to forces like natural selection, genetic drift, mutation, and gene flow.
This topic dives into calculating allele frequencies, Hardy-Weinberg equilibrium, and real-world examples of microevolution. It shows how small genetic changes can lead to big evolutionary shifts, connecting the dots between genes and natural selection.
Population genetics and evolution
Definition and role in studying evolutionary processes
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Population genetics is the study of the distribution and change in allele frequencies within populations over time and space
Uses mathematical models to analyze and predict how evolutionary forces such as natural selection, genetic drift, mutation, and gene flow influence the genetic composition of populations
Plays a crucial role in understanding the mechanisms of microevolution, which refers to evolutionary changes within species or populations
Principles can be applied to various areas, including conservation biology, animal and plant breeding, and understanding the evolution of disease resistance in pathogens
Provides a framework for testing hypotheses about the evolutionary history and future of populations using empirical data and statistical analyses
Allele and genotype frequencies
Calculating frequencies within populations
Allele frequency is the proportion of a specific allele at a given locus within a population
Calculated by dividing the number of copies of the allele by the total number of alleles at that locus in the population
Genotype frequency is the proportion of individuals in a population with a specific genotype
Calculated by dividing the number of individuals with the genotype by the total number of individuals in the population
Hardy-Weinberg equilibrium and deviations
The Hardy-Weinberg equilibrium principle states that allele and genotype frequencies in a population remain constant from generation to generation in the absence of evolutionary influences (natural selection, genetic drift, mutation, and gene flow)
The Hardy-Weinberg equation (p2+2pq+q2=1) can be used to calculate the expected genotype frequencies in a population, given the allele frequencies, assuming the population is in Hardy-Weinberg equilibrium
Deviations from the expected Hardy-Weinberg genotype frequencies can indicate the presence of evolutionary forces acting on the population
Genetic drift, gene flow, and mutation
Genetic drift and its effects on populations
Genetic drift is the random change in allele frequencies due to sampling effects in finite populations, leading to the loss of genetic variation over time
The impact of genetic drift is more pronounced in small populations, where the random sampling of alleles from one generation to the next can cause significant changes in allele frequencies
Founder effect and population bottlenecks are examples of genetic drift that can result in reduced genetic diversity and the fixation or loss of alleles in populations
Gene flow and its influence on allele frequencies
Gene flow is the transfer of alleles between populations through migration or interbreeding, which can introduce new alleles or change the frequencies of existing alleles in a population
Can counteract the effects of genetic drift and natural selection by homogenizing allele frequencies across populations
The rate and direction of gene flow can be influenced by factors such as geographical barriers, dispersal abilities, and mating preferences
Mutation as a source of genetic variation
Mutation is the ultimate source of new genetic variation in populations, involving changes in the DNA sequence that can create new alleles or modify existing ones
The rate of mutation is typically low, but over evolutionary time, mutations can accumulate and contribute to the genetic diversity within and among populations
Mutations can be neutral, beneficial, or deleterious, and their fate in a population depends on the interplay of evolutionary forces such as natural selection and genetic drift
Population genetics in microevolution
Real-world examples of microevolution
Pesticide resistance in insects is an example of microevolution driven by natural selection
Alleles conferring resistance to pesticides increase in frequency over generations due to the selective pressure of pesticide application
The evolution of antibiotic resistance in bacteria showcases microevolution
Mutations conferring resistance to antibiotics are selected for in the presence of antibiotic treatment, leading to the spread of resistant strains in bacterial populations
The peppered moth (Biston betularia) in England underwent a rapid change in color morph frequencies during the Industrial Revolution
The dark morph became more common in polluted areas due to better camouflage against predators on soot-covered trees, demonstrating the effects of natural selection on allele frequencies
The evolution of beak size and shape in Galápagos finches, as studied by Peter and Rosemary Grant, showcases how natural selection can lead to rapid changes in allele frequencies and morphological traits in response to fluctuations in food availability and competition
Balancing selection in human populations
The genetic basis of sickle cell anemia in human populations is an example of balancing selection
The heterozygous genotype (HbA/HbS) confers resistance to malaria, while the homozygous genotype (HbS/HbS) causes sickle cell anemia
Balancing selection maintains both alleles in the population at an equilibrium frequency