Chapter 23 Flashcards
evolutionary change below the species level; change in the allele frequency in a population over generations.
microevolution
the percent, on average, of a population’s loci that are heterozygous in members of the population.
average heterozygosity
a change in the nucleotide sequence of an organism’s DNA, ultimately creating genetic diversity. They also occur in the DNA or RNA of a virus.
mutation
differences between the gene pools of geographically separate populations or populations subgroups.
geographic variation
a graded change in a character along a geographic axis.
cline
a localized group of individuals of the same species that can interbreed, producing fertile offspring.
population
the aggregate of all of the alleles for all of the loci in all individuals in a population. The term is also used in a a more restricted sense as the aggregate of alleles for just one or a few loci in a population.
gene pool
the condition describing a non evolving population (one that is in genetic equilibrium).
Hardy-Weinberg equilibrium
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 principle
a process in which change events cause unpredictable fluctuations in allele frequencies from one generation to the next. Effects are most pronounced in small populations.
genetic drift
genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions. Typically, the surviving population is no longer genetically representative of the original population.
bottleneck effect
genetic drift that 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 population.
founder effect
the transfer of alleles from one population to another, resulting from the movement of fertile individuals or their gametes.
gene flow
the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals in the population.
relative fitness
natural selection in which individuals at one end of the phenotypic range survive or reproduce more successfully than do other individuals.
directional selection
natural selection in which individuals on both extremes of a phenotypic range survive or reproduce more successfully than do individuals with intermediate phenotypes.
disruptive selection
natural selection in which intermediate phenotypes survive or reproduce more successfully than do extreme phenotypes.
stabilizing selection
a form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.
sexual selection
marked differences between the secondary sex characteristics of males and females.
sexual dimorphism
a direct competition among individuals of one sex (usually the males in vertebrates) for mates of the opposite sex.
intrasexual selection
selection whereby individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex; also called mate choice.
intersexual selection
natural selection that maintains two or more phenotypic forms in a population.
balancing selection
greater reproductive success of heterozygous individuals compared with homozygotes; tends to preserve variation in a gene pool.
heterozygote advantage
a decline in the reproductive success of individuals that have a phenotype that has become too common in a population.
frequency-dependent selection
genetic variation that does not appear to provide a selective advantage or disadvantage.
neutral variation
