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a trait that increases the ability of an individual to survive and reproduce compared to individuals without the trait

adaptive radiation

the rise of many new species in a relatively short time as a result of a single species that invades different habitats and evolves under different environmental pressures in those habitats

allele frequency

for any given gene, the relative proportion of each allele of that gene in a population

directional selection

a type of natural selection in which one extreme phenotype is favored over all others

disruptive selection

a type of natural selection in which both extreme phenotypes are favored over the average phenotype

founder effect

a type of genetic drift in which an isolated population founded by a small number of individuals may develop allele frequencies that are very different from those of the parent population as a result of chance inclusion of disproportionate numbers of certain alleles in the founders

sympatric speciation

speciation that occurs in populations that are not physically divided; normally due to ecological isolation or chromosomal aberrations


the basic unit of taxonomic classification


the process of species formation, in which a single species splits into two or more species

reproductive isolation

the failure of organisms of one population to breed successfully with members of another, may be due to premating or postmating isolating mechanisms

geographical isolation

the separation of two populations by a physical barrier

gene flow

the movement of alleles from one population to another owing to the migration of individual organisms

gene pool

the total of all alleles of all genes in a population; for a single gene, the total of all the alleles of that gene that occur in a population

genetic drift

a change in the allele frequencies of a small population purely by chance

hardy-weinberg principle

a mathematical model proposing that, under certain conditions, the allele frequencies and genotype frequencies in a sexually reproducing population will remain constant over generations

natural selection

the unequal survival and reproduction of organisms due to environmental forces (survival of the fittest)

allopatric speciation

speciation that occurs when two populations are separated by a physical barrier that prevents gene flow between them (geographical isolation)

ecological isolation

the lack of mating between organisms belonging to different populations that occupy distinct habitats within the same general area

gamete incompatibility

the inability of sperm from one species to fertilize eggs of another species


having more than two homologous chromosomes of each type

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