Chapter 23: The Evolution of Populations Flashcards

This set of vocabulary flashcards covers key concepts from Chapter 23 on population evolution, including mechanisms like natural selection, genetic drift, gene flow, and the principles of Hardy-Weinberg equilibrium.

Smallest unit of evolution

The population; it is individuals that are acted upon by natural selection, but only populations evolve.

Mutations

Changes in the nucleotide sequence of DNA that serve as the source of new alleles and genes.

Point mutation

A change in one nucleotide base in a gene.

Chromosomal mutations

Changes that delete, disrupt, or rearrange many loci on a chromosome.

Mutation rate

Averages $1$ in every $100,000$ genes per generation.

Sexual Recombination

The process in sexually reproducing organisms that produces most of the variability in each generation.

Discrete characters

Characters classified on an either-or basis, such as flower color in pea plants.

Quantitative characters

Characters that vary along a continuum within a population, such as height or weight.

Hardy-Weinberg equilibrium

The state of a population that is not evolving, meaning allele frequencies do not change over time.

Five assumptions of Hardy-Weinberg equilibrium

No mutations, large population size, no gene flow, no natural selection, and random mating.

Allele frequency formula

$p + q = 1$, where $p$ is the frequency of allele 1 and $q$ is the frequency of allele 2.

Hardy-Weinberg genotype equation

$p^2 + 2pq + q^2 = 1$, where $p^2$ and $q^2$ are homozygous frequencies and $2pq$ is the heterozygous frequency.

Natural Selection

A mechanism of evolution where alleles are passed to the next generation in proportions differing from the present based on high fitness traits.

Genetic Drift

Unpredictable fluctuations in allele frequencies from one generation to the next, specifically significant in smaller populations.

Bottleneck Effect

A sharp reduction in the size of a population due to environmental events or human activities, leading to reduced genetic variation.

Founder Effect

The loss of genetic variation that occurs when a small population of individuals establishes itself away from a larger population.

Gene Flow

Genetic additions to or subtractions from a population resulting from the movement of fertile individuals or gametes; it tends to reduce variation among populations.

Evolutionary Fitness

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

Directional selection

A mode of selection that favors individuals at one extreme end of the phenotypic range.

Disruptive selection

A mode of selection that favors individuals at both extremes of the phenotypic range.

Stabilizing selection

A mode of selection that favors intermediate variants and acts against extreme phenotypes.

Sexual Selection

A type of selection that favors traits giving an individual a competitive edge in attracting or keeping a mate.

Intrasexual selection

Direct competition among individuals of one sex for mates of the opposite sex.

Intersexual selection

Occurs when individuals of one sex (usually females) are choosy in selecting their mates from the other sex.

Sexual dimorphism

Marked differences between the secondary sex characteristics of males and females of the same species.

Diploidy

The state of having two sets of chromosomes, which maintains genetic variation in the form of hidden recessive alleles.

Balancing selection

Occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population.

Frequency-dependent selection

A condition where the fitness of a phenotype depends on how common it is in the population.

Heterozygote advantage

Occurs when individuals who are heterozygous at a particular locus have greater fitness than both kinds of homozygotes, such as the sickle-cell allele conferring malaria resistance.