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Microevolution
evolution on the smllest scale as change in the allele frequency over generations
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Genetic Variation
Differences among individuals in the composition on their genes or other DNA segments
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Average heterozygosity
The average percentage of loci that are heterozygous
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Geographic variation
Differences in the genetic composition of separate population
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Cline
A graded change in a character along a geographic axis
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Population
A group of individuals of the same species that live in the same area and interbreed, producing fertile offspring
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Gene pool
Consists of all copies of every type of allele at every locus in all members of the population
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Hardy-weinberg principle
The gene pool of a population that is not evolving
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Genetic drift
Chance events that cause allele frequencies to fluctuate unpredictably from one generation to the next, especially in small populations
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Founder effect
When a few individuals become isolated from a large population, this small group may establish a new population whose gene pool differs from the source population
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Bottleneck effect
A sudden change in the environment, such as a fire or flood, may drastically reduce the population size
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Gene flow
The transfer of allele into or out of a population due to the movement of fertile individual or their gametes
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Relative fitness
The contribution an individual makes to the gene pool of the next generation relative to the contribution of other individuals
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Directional selection
When conditions favor individuals exhibiting one extreme of a phenotypic range, thereby shifting a population's frequency curve in one direction or the other
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Disruptive selection
When conditions favor individuals at both extremes of the phenotypic range over individuals with intermediate phenotypes
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Stabilizing selection
Acts against both extreme phenotypes and favors intermediate variants
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Sexual selection
A form of selection in which individuals with certain inherited characteristics are more likely than other individauls to obtain mates
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Sexual dimorphism
A difference between two sexes in secondary sexual characteristics
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Intrasexual selection
Selection within the same sex, individuals of the same sex compete directly for mates of the opposite sex
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Intersexual selection
Mate choice, individuals of one sex are choosy in selecting their mates from the other sex
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Neutral variation
Difference in DNA sequence that do not confer a selective advantage or disadvantage
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Balancing selection
When natural selection maintains two or more forms in a population
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Heterozygote advantage
Individuals who are heterozygous at a particular locus have greater fitness than do both kinds of homozygous
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Frequency -dependent selection
The fitness of a phenotype depends on how common it is in the population
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