Lecture 6: Selection and Mutation
Mendelian genetics: The law of inheritance proposed by Gregor Mendel which includes the law of segregation and the law of independent assortment.
Population genetics: The synthesis of Mendelian genetics and Darwinian evolution.
Allele frequency: The percentages of different alleles within a population.
Genotype frequency: The percentages of different genotypes within a population.
Heterozygote frequency: The fraction of the population that has a dominant and recessive allele.
Homozygote frequency: The fraction of the population that has either both dominant alleles or both recessive alleles.
Genetic drift: Change in the frequencies of alleles in a population resulting from sampling error in drawing gametes from a gene pool to make zygotes and from chance variation in the survival and/or reproductive success of individuals; results in nonadaptive evolution.
Overdominance/Heterozygote superiority: A situation where heterozygotes at a particular locus tend to have higher fitness than homozygotes.
Underdominance/ Homozygote superiority: A situation where heterozygotes at a particular locus tend to have lower fitness than homozygotes.
Frequency-dependent selection: Occurs when an individual's fitness depends on the frequency of its phenotype in the population.
Mutation-selection balance: An equilibrium in the frequency of an allele that occurs because new copies of the allele are created by mutation at exactly the same rate that old copies of the allele are eliminated by natural selection.
Mutation accumulation experiment: Lineages of organisms are insulated as much as possible from natural selection, and are thus allowed to accumulate mutations by genetic drift.
Mutation rate: The change in frequency of mutations accumulated each generation.
Hardy Weinberg Equilibrium: A situation in which allele and genotype frequencies in an ideal population do not change from one generation to the next, because the population experiences no selection, no mutation, no migration, no genetic drift, and random mating.
Lecture 7: Migration, Genetic Drift, and Non-random Mating I
Migration: In evolution, the movement of alleles from one population to another, typically via the movement of individuals or via the transport of gametes by wild, water, or pollinators.
Gene flow: The movement of alleles from one population to another population.
Gene pool: The set of all copies of all alleles in a population that could potentially be contributed by the members of one generation to the members of the next generation.
Sampling error: A change difference between the frequency of a trait in a subset of individuals from a population versus the frequency of the trait in the entire population.
Founder effect: A change in allele frequencies that occurs after a founder event (establishment of a new population), due to genetic drift in the form of sampling error in drawing founders from the source population.
Fixation index (Fst): A statistic that calculates how fixed an allele is on a scale of 0 to 1.
Effective population size (Ne): The size of an ideal random mating population (with no selection, mutation, or migration) that would lose genetic variation via drift at the same rate as is observed in an actual population.
Genetic polymorphism: The existence of within a population of more than one variant for a phenotypic trait, or of more than one allele.
Fixation: The elimination from a population of all the alleles at a locus but one; the one remaining allele, now at a frequency of 1.0, is said to have achieved fixation, or to be fixed.
Lecture 8: Migration, Genetic Drift, and Non-random Mating II
Positive selection: Selection in favor of advantageous mutations.
Negative selection: Selection against deleterious mutations. Also called purifying selection.
Neutral theory: A theory that models the rate of fixation of alleles with no effect on fitness; also associated with the claim that the vast majority of observed base substitutions are neutral with respect to fitness.
Selectionist theory: The viewpoint that natural selection is responsible for a significant percentage of substitution events observed at the molecular level.
Synonymous mutations (dS): A DNA substitution that does not change the amino acid or RNA sequence specified by the gene. Also called a silent (or silent-site) substitution.
Non-synonymous mutations (dN): A DNA substitution that changes the amino acid sequence specified by the gene.
Inbreeding: Mating among kin.
Inbreeding depression: Reduced fitness in individuals or populations resulting from kin matings; often due to the decrease in heterozygosity associated with kin matings, either because heterozygotes are superior or because homozygotes for deleterious alleles become more common.
Genetic load: Reduction in the mean fitness of a population due to the presence of deleterious alleles.
Mutational meltdown: Exposure of deleterious mutations due to inbreeding results in a reduction in population size, making drift more effective. This increases the rate at which deleterious mutations are fixed, snowballing the problem.
Assisted migration: To bolster genetic diversity and rescue populations from inbreeding depression.
Lecture 9: Linkage and Sex
Multi-locus: Multiple loci on a genotype.
Linkage equilibrium: When genotypes at one locus are randomly distributed with respect to genotypes at another locus.
Linkage Disequilibrium: When genotypes at one locus are not randomly distributed with respect to genotypes at another locus.
Haplotype: Genotype for a suite of linked loci on a chromosome; typically used for mitochondrial genotypes, because mitochondria are haploid and all loci are linked.
Coefficient of linkage disequilibrium (D)
Population admixture: Lack of migration between populations means that while each population might be in equilibrium, if those populations are mixed together, the resulting population is in LD.
Genetic recombination: The placement of allele copies into multilocus genotypes (on chromosomes or within gametes) they are different from the multilocus genotypes they belonged to in the previous generations; results from meiosis with crossing over and sexual reproduction with outcrossing.
Random mating: Mixes up combinations of alleles at a given locus, increases genotypic variation.
Neutral mutations: A mutation that has no effect on fitness of the bearer.
Genetic Hitchhiking: Change in the frequency of an allele due to positive selection on a closely linked locus.
Parthenogenesis: A reproductive mode in which offspring develop from unfertilized eggs.
Outcrossing: Mating among unrelated individuals.
Muller’s Ratchet: Genetic drift that fixes deleterious alleles in; cannot go back to recover alleles without the deleterious mutations.
Red Queen Hypothesis: States that two biological antagonists must keep evolving to avoid extinction.
Lecture 10: Quantitative Genetics
Quantitative trait: A trait for which phenotypes do not fall into discrete categories, but instead show continuous variation among individuals; a trait determined by the combined influence of the environment and many loci of small effect.
Qualitative trait: A trait for which phenotypes fall into discrete categories (such as affected versus unaffected with cystic fibrosis).
Quantitative trait locus: A locus at which there is genetic variation that contributes to the phenotypic variation in a quantitative trait.
QTL mapping: A collection of techniques that allow researchers to identify chromosomal regions containing loci that contribute to quantitative traits.
Candidate loci: A locus on a specific gene.
Heritability: In the broad sense, that fraction of the total phenotypic variation in a population that is caused by genetic differences among individuals; in the narrow sense, that fraction of the total variation that is due to the additive affects of genes.
Genetic variation (VG): Differences among individuals in a population that are due to differences in genotype.
Environmental variation (VE): Differences among individuals in a population that are due to differences in the environments they have experienced.
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