Microevolution is the evolution of one population or one species over a short period of time. We can study microevolution by observing the traits of various organisms within a species and how those traits’ purposes fit into the species’ ecological niche. We combine our knowledge of Mendelian inheritance and Darwin’s theory of evolution to predict how a species will change over time.
Microevolution: Evolution over a short period of time within a small population or just one species.
Population Genetics: Combines Darwin’s evolutionary theory and the principles of Mendelian inheritance.
Gene Pool: All genes in a population.
Allele Frequency: How often an allele shows up in a population.
Genetic Diversity: How many different alleles there are in a gene pool.
Hardy-Weinberg Theorem: Founding principle of population genetics that proves allele and genotype frequencies do not change in a population that meets the conditions of no mutation, no migration, large population size, random mating, and no natural selection.
Gene Flow: A change in allele frequencies in a population due to movement in and out of a population.
Genetic Drift: TA change in allele frequencies in a small
Disruptive Selection: Type of natural selection for a polygenic trait in which phenotypes in the middle of the phenotypic distribution are selected against, resulting in two overlapping phenotypes, one at each end of the distribution.
Stabilizing Selection: T Type of natural selection for a polygenic trait in which phenotypes at both extremes of the phenotypic distribution are selected against, resulting in a narrowing of the range of phenotypic variation.
Directional Selection: Type of natural selection for a
polygenic trait in which one of two extreme phenotypes is selected for, resulting in a shift of the phenotypic distribution toward that extreme.
Sexual Dimorphism: Differences between the phenotypes of males and females of the same species.
Population genetics is a part of microevolution that looks at evolution within a population.
If all conditions of the Hardy-Weinberg theorem are met, the allele and genotype frequencies will never change in a population. Because this is not realistic, as it is very unlikely for all five conditions to be met in any particular population, we can use this theorem as the foundation of our understanding the changes in allele frequency in a population. If there is a change in allele frequency, we know that at least one of the conditions of the Hardy-Weinberg theorem was not met. The five conditions of the Hardy-Weinberg theorem are:
The Hardy-Weinberg equation is: p² + 2pq + q² = 1
The variables P and q represent the frequencies of two different alleles for a genotype, and this equation determines approximately what percentage each allele should occupy, if all the conditions of this theorem are met. P² and q² represent homozygous genotypes, while Pq represents the heterozygous genotypes.
Ways that natural selection affects phenotypes:
The phenotype distribution is shifted towards the middle, and both extremes eventually die off.
The phenotype of the species in the environment will shift towards one extreme over time.
The phenotypes of this species is distributed between the two extremes, and the number of organisms with the intermediate phenotypes decreases.