Exam 1 Flashcards
Heterozygosity
The frequency of heterozygosity in a population. H=2pq. A measure of genetic variation in populations - a critical condition for the process of evolution to take place.
Homology
Similarity of structure due to descent from a common ancestor. Demonstrates a common genetic basis for similar characters in different organism provides evidence for inheritance of those characters.
Clinal Variation
Change in the phenotype of organism across geographic transect, usually showing a gradient of from one end to the other. Demonstrates variation among populations; can provide evidence that natural selection has operated; or can be used to examine the balance of gene flow and selection.
Modern Synthesis
The synthesis of mathematics, Mendelian genetics and evolutionary theory that produced the foundation of population genetics. Provided a strong quantitative basis for the mechanisms of evolutionary change at the genetic level.
Functional Constraints
The degree of which a trait or nucleotide position can be changed without altering the fitness of the carrier. High functional constraints leads to slow rates of evolutionary change, low functional constraints permits change by the action of mutation. Useful predictor of the expected rate of evolutionary divergence in molecular evolution
Intrademic Selection
Selection within a local population (deme), leading to the change in allele frequencies in local population only
Interdemic Selection
Selection between populations due too different average fitness values in different populations.
Delta p
Change in allele frequency during one (or more) generations of evolution. Can be due to any evolutionary forces (selection, mutation, migration, drift)
wbar
Weighted average fitness in the population
Adaptation
A trait that increases the ability of an individual to survive or reproduce compared with individuals without the trait.
Eidos
Platonic concept of idealized form. Applies to the problem of species concept and the notion that species are fixed entities. Possibly diverted attention away from the concept of change and evolutionary thinking.
Homozygosity
The proportion of homozygotes in the population. A measure of gene identity, as p2 + q2 , or more generally, sum(xi2) where xi is the frequency of the ith allele. The opposite of genetic variation.
Underdominance
Selection against heterozygotes. Causes disruptive selection and can lead to distinct phenotypes in a population, possibly speciation
Marginal overdominance
Heterozygote advantage due to alternative homozygotes being favored in alternative environments. When the fitnesses are appropriate, the average fitness across niches or environments can result in the heterozygote have the highest average fitness even though it may not be favored in any one habitat.
Hitchhiking
The increase in frequency of a neutral marker due to selection acting at a linked marker. A more general definition is: evolutionary change at a marker due to the action of an evolutionary force at a linked marker, but is often associated with selection and selective sweeps. A selective sweep results in the sweeping out of variation due to hitchhiking by linked markers
Purifying selection
removal of deleterious alleles from the population.
Inbreeding
mating between individuals who share ancestry (are relatives). This leads to the loss of heterozygosity.
Isolation by distance
is the divergence of allele frequencies between populations that are separated by some geographic distance.
Uniformitarionism
The notion that the forces that shape earth history are the same now as have been operating for millions of years. Mountain building by tectonic forces, erosion, weathering, etc. have shaped geological forms and left a history of change on the planet. Counter to catastrophism, and important in supporting Darwin’s ideas of a long time for earth history, hence a long time for evolutionary change. It was advocated by Lyell in Principles of Geology
Dominance coefficient, h
A quantity between 0 and 1 that determines the degree of dominance acting on the heterozygote. When h=0 the one allele is dominant, when h = 1 the other allele is dominant and when h=0.5 there is strict co-dominance. This can affect the ability of natural selection to act on genetic variation as h determines what genotypes are affected by selection when h is applied to fitness.
Multiple nitch polymorphism
A polymorphism that is maintained by selection acting in multiple niches, and specifically when one allele or genotypes I favors in one niche and the alternative allele (genotype) is favored in the other niche. This can maintain alleles in balancing selection due to heterogeneous selection acting in different niches.
Stabilizing selection
Selection that maintains the mean of a population by selecting against the tails or extremes. Balancing selection is one form of stabilizing selection. This can maintain variation in populations and can result in little change in phenotype over time, despite the action of selection.
Fst
The fixation of alleles in sub-populations relative to the total population. Defined as (Htotal – Haverage)/Htotal where H is 2pq or heterozygosity. Fst is high when subpopulations have different allele frequencies and low when populations have the same allele frequencies. A measure of population structure.
Selective sweep
removal of polymorphism from a genomic region due to the action of selective fixation of a beneficial allele.
Absolute fitness
some component of survival or reproduction based on absolute terms, such as lifespan, percent survival, number of offspring
Relative fitness
the fitness of a particular genotype relative to the best genotype in the population.
Vestigial structure
A structure that is more pronounced or evident in an ancestor than in a descendant indicating a loss of function in the descendant. Provides evidence for descent with modification, and general definition of evolution
Mutation-selection balance
A balance of evolutionary forces (mutation and selection) that can maintain variation in a population. If a deleterious allele is introduced by mutation, but removed by selection it can be maintained by this balance. Evidence for the interaction of evolutionary forces.
Frequency dependent selection
Selection on an allele that varies with the frequency of that allele. Typically this involves rare-allele advantage, so the alleles cycle, such that it increases when rare but decreases when common. A process that can maintain genetic variation in populations
Founder effect
The establishment of a population by a small number of founders, leading to the loss of genetic variation and imposing genetic drift on the population. A process where evolution can occur by non-selective forces, and can be important in generating population structure or variation between populations.
Candidate Gene
a gene whose function is known and is a likely genetic factor in explaining variation in a particular phenotype (melanocortical receptor for pigmentation).
Neutral marker
A neutral marker is a SNP or other genetic marker that has no known function or is believed not to be related to the trait being studied.
Allele
A variant form of a gene. The raw material upon which selections acts.
Fitness
Genetic contribution to future generations. Relative survivorship and reproduction. The metric tat defines the strength of selection.
Epistasis
Interactions among alleles at separate loci. Genotype x genotype interaction where the phenotype of one locus’ genotype depends on the second locus. A source of genetic variation.
Isolation by distance
The decline in genetic similarity with distance due to reduced opportunity for gene flow. Demonstrates how gene flow can homogenize a population when high, but allow divergence when low.
