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Population Genetics
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Founder Effect
A type of genetic drift describing the loss of allelic variation that occurs when a new population is established by a very small number of individuals. Significance: Can lead to a population that is genetically distinct from the original population.
Disruptive Selection
Type of natural selection that favors extreme values of a trait over intermediate values. Significance: This type of selection can lead to a bimodal distribution of trait values and can contribute to sympatric speciation.
Inbreeding Depression
A reduction in biological fitness in a given population as a result of inbreeding, or breeding of related individuals. Significance: Can lead to an increased prevalence of harmful genetic variants.
Hardy-Weinberg Equilibrium
A principle stating that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors. Significance: Provides a baseline for detecting evolutionary influences and estimating allele frequencies in a population.
Phenotypic Plasticity
The ability of an organism to change its phenotype in response to changes in the environment. Significance: Allows for survival in varying environments and may have a genetic basis that can be selected for by natural selection.
Population Bottleneck
A reduction in the genetic diversity of a population caused by a reduction in its size. Significance: Can lead to a change in the population structure and potential survival challenges due to reduced genetic variability.
Bottleneck Effect
A sharp reduction in the size of a population due to environmental events or human activities. Significance: Can result in a substantial reduction in genetic diversity and an increase in inbreeding.
Selection Coefficient (s)
A measure of the relative fitness reduction associated with a genetic variant compared to the wild type. Significance: It quantifies the strength of selection against a genotype; the higher the selection coefficient, the stronger the selection.
Directional Selection
Type of natural selection that favors one extreme phenotype over the mean or other extremes. Significance: Leads to a change in the population mean toward the favored phenotype and can cause a shift in allele frequencies over time.
Allopatric Speciation
The formation of a new species in populations that are geographically isolated from one another. Significance: It's a common mode of speciation and can occur via reproductive isolation after a physical barrier divides a population.
Fitness (W)
The genetic contribution of an individual to the next generation's gene pool compared to the average for the population. Significance: Indicates the reproductive success of a phenotype or genotype.
Genetic Drift
The change in the frequency of an existing gene variant in a population due to random sampling of organisms. Significance: Can lead to the loss of genetic variation and potentially to the fixation or loss of alleles.
Gene Flow
The transfer of genetic variation from one population to another. Significance: Can increase genetic variation within a population and reduce differences between populations.
Balancing Selection
Natural selection that maintains two or more phenotypic forms in a population. Significance: Can lead to a stable polymorphism in the population, maintaining multiple alleles at higher frequencies than would be expected.
Gene Pool
The set of all genes, or genetic information, in any population, usually of a particular species. Significance: Represents the full set of genetic variants that can be drawn on for the process of natural selection.
Natural Selection
The differential survival and reproduction of individuals due to differences in phenotype. Significance: It's the process by which beneficial heritable traits become more common in successive generations.
Mutation
The change of the structure of a gene, resulting in a variant form that may be transmitted to subsequent generations. Significance: Source of new alleles and thus genetic variation, which is essential for evolution.
Linkage Disequilibrium
The non-random association of alleles at different loci in a given population. Significance: Can inform us about the population history and the forces of evolution acting upon the genome.
Stabilizing Selection
Type of natural selection in which genetic diversity decreases as the population stabilizes on a particular trait value. Significance: Tends to remove the extremes of trait distributions, thereby maintaining the status quo.
Biological Species Concept
The definition of a species as a group of populations that can interbreed and produce fertile offspring but cannot do so with other such groups. Significance: Used to distinguish species from one another by sexual compatibility.
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