AP Bio Chapter 23 The Evolution of Populations

Microevolution

Evolutionary change below the species level; change in the genetic makeup of a population from generation to generation.

Population genetics

The study of how populations change genetically over time

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.

Population

A localized group of individuals that belong to the same biological species (that are capable of interbreeding and producing fertile offspring).

Gene pool

The total aggregate of genes in a population at any one time.

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.

Conditions of Hardy-Weinberg Equilibrium

1. Extremely large population size: The smaller the population, the greater the role played by chance fluctuations in allele frequencies from one generation to the next, known as genetic drift.
2. No gene flow: Gene flow, the transfer of alleles between p

Mutations

Changes in the DNA of a gene, ultimately creating genetic diversity.

Genetic Drift

Unpredictable fluctuations in allele frequencies from one generation to the next because of a population?s finite size

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.

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.

Gene flow

Genetic additions to or substractions from a population resulting from the movement of fertile individuals or gametes.

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

Morphs

The potential phenotypic variants of an organism. When individuals differ in a discrete character, the different forms are called ______________________.

Genetic Polymorphism

The existence of two or more distinct alleles at a given locus in a population?s gene pool.

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 separate populations or population subgroups

Cline

A graded variation in a trait that parallels a gradient in the environment

Fitness

The contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals.

Relative Fitness

The contribution of one genotype to the next generation compared to that of alternative genotypes for the same locus

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.

Stabalizing Selection

Natural selection that favors intermediate variants by acting against extreme phenotypes

Balancing Selection

Natural selection that maintains stable frequencies of two or more phenotypic forms in a population (balanced polymorphism)

Balanced Polymorphism

The ability of natural selection to maintain diversity in a population.

Heterozygote advantage

Greater reproductive success of heterozygous individuals compared to homozygotes; tends to preserve variation in gene pools.

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.

Neutral Variation

Genetic diversity that confers no apparent selective advantage.

Pseudogenes

DNA segments very similar to a real gene but which do not yield a functional product; a gene that has become inactivated in a particular species because of mutation.

Sexual Selection

Natural selection for mating success.

Sexual Dimorphism

A special case of polymorphism based on the distinction 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; also called mate choice.