Biology 191 ch. 23

evolutionary change below the species level; change in the allele frequencies in a population over generations
average heterozygosity
the percent, on average, of a population's loci that are heterozygous in members of the population
geographic variation
differences between the gene pools of geographically seperate populations or population subgroups
a graded change in a character along a geographic axis
a change in the nucleotide sequence of an organism's DNA, ultimately creating genetic diversity; in a virus it can occur in the DNA or RNA
a localized group of individuals of the same species that can interbreed, producing fertile offspring
gene pool
the aggregate of all of the alleles for all of the loci in all individuals in a population
Hardy-Weinberg principle
the principle that frequencies of alleles and genotypes in a population remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work
Hardy-Weinberg equilibrium
the condition describing a nonevolving population
adaptive evolution
evolution that results in a better match between organisms and their environments
genetic drift
a process in which chance events caues unpredicatble fluctuations in allele frequencies from one generation to the next; most pronounced in small populations
founder effect
genetic drift taht occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original pool
bottleneck effect
genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions; the surviving population is no longer genetically representative of the original population
gene flow
the transfer of alleles from one population to another, resulting from the movement of fertile individuals or their gametes
relative fitness
the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals in the population
directional selection
natural selection in which individuals at one end of the phenotypic range survive or reproduce more succesffully than do other individuals
disruptive selection
natural selection in which individuals on both extemes of a phenotypic range survive or reproduce more successfully than do individuals with intermediate phenotypes
stabilizing selection
natural selection in which intermediate phenotypes survive or reproduce more successfuly than do extreme phenotypes
sexual selection
a form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates
sexual dimorphism
marked differences between the secondary sex characteristics of males and females
intrasexual selection
a direct competition among individuals of one sex (usually the males in vertebrates) for mates of the opposite sex
intersexual selection
selection whereby individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex; mate choice
balancing selection
natural selection that maintains two or more phenotypic forms in a population
heterozygote advantage
greater reproductive success of heterozugoous individuals compared with homozygotes; tends to preserve variation in a gene pool
frequency-dependent selection
a decline in the reproductive success of individuals that have a phenotype that has become too common in a population
neutral variation
genetic variation that does not appear to provide a selective adavantage or disadvantage