AP Bio Midterm Key Terms Ch. 23 Flashcards
average heterozygosity
The percent, on average, of a population’s loci that are heterozygous in members of the population.
balanced polymorphism
The ability of natural selection to maintain diversity in a population.
balancing selection
Natural selection that maintains stable frequencies of two or more phenotypic forms in a population (balanced polymorphism).
bottleneck effect
Genetic drift resulting from the reduction of a population, typically by a natural disaster, such that the surviving population is no longer genetically representative of the original population.
cline
A graded variation in a trait that parallels a gradient in the environment.
directional selection
Natural selection that favors individuals at one end of the phenotypic range.
disruptive selection
Natural selection that favors individuals on both extremes of a phenotypic range over intermediate phenotypes.
fitness
The contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals.
founder effect
Genetic drift that occurs when a few individuals become isolated from a larger population, with the result that the new population’s gene pool is not reflective of the original population.
frequency-dependent selection
A decline in the reproductive success of a morph resulting from the morph’s phenotype becoming too common in a population; a cause of balanced polymorphism in populations.
gene flow
Genetic additions to or substractions from a population resulting from the movement of fertile individuals or gametes.
gene pool
The total aggregate of genes in a population at any one time.
genetic drift
Unpredictable fluctuations in allele frequencies from one generation to the next because of a population’s finite size.
genetic polymorphism
The existence of two or more distinct alleles at a given locus in a population’s gene pool.
geographic variation
Differences between the gene pools of separate populations or population subgroups.
Hardy-Weinberg equilibrium
The condition describing a non-evolving population (one that is in genetic equilibrium).
Hardy-Weinberg theorem
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.
heterozygote advantage
Greater reproductive success of heterozygous individuals compared to homozygotes; tends to preserve variation in gene pools.
intersexual 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.
intrasexual selection
A direct competition among individuals of one sex (usually the males in vertebrates) for mates of the opposite sex.
microevolution
Evolutionary change below the species level; change in the genetic makeup of a population from generation to generation.
modern synthesis
A comprehensive theory of evolution emphasizing populations as units of evolution and integrating ideas from many fields, including genetics, statistics, paleontology, taxonomy, and biogeography.
mutation
A rare change in the DNA of a gene, ultimately creating genetic diversity.
neutral variation
Genetic diversity that confers no apparent selective advantage.
phenotypic polymorphism
The existence of two or more distinct morphs (discrete forms), each represented in a population in high enough frequencies to be readily noticeable.
polymorphism
The coexistence of two or more distinct forms in the same population.
population
A localized group of individuals that belong to the same biological species (that are capable of interbreeding and producing fertile offspring).
population genetics
The study of how populations change genetically over time.
pseudogene
A DNA segment very similar to a real gene but which does not yield a functional product; a gene that has become inactivated in a particular species because of mutation.
relative fitness
The contribution of one genotype to the next generation compared to that of alternative genotypes for the same locus.
sexual dimorphism
A special case of polymorphism based on the distinction between the secondary sex characteristics of males and females.
stabilizing selection
Natural selection that favors intermediate variants by acting against extreme phenotypes.
