Chapter 23: The Evolution of Populations

Vocabulary flashcards covering key terms from the lecture notes on population genetics and evolution (microevolution, Hardy-Weinberg, drift, gene flow, selection, and related concepts).

Microevolution

The change in allele frequencies in a population over generations; evolution at the smallest scale.

Natural selection

Adaptive evolution where individuals with favorable heritable traits have higher reproductive success.

Genetic drift

Random fluctuations in allele frequencies due to chance events; effects are stronger in small populations.

Gene flow

Movement of alleles among populations; can erase differences if strong and may introduce useful variation.

Genetic variation

Differences in genes or DNA sequences among individuals; essential for evolution; phenotype results from genotype and environment.

Phenotype

Observable traits of an organism, produced by the interaction of its genotype and the environment.

Genotype

The genetic makeup of an individual; the set of alleles at one or more loci.

Germ line mutation

Mutations in the cells that give rise to gametes; only these mutations can be inherited.

Mutation

Origin of new genes and alleles; often arises from replication/recombination errors; most are neutral, some harmful, some beneficial.

Noncoding DNA (junk DNA)

DNA that does not code for proteins; mutations here often have no effect on phenotype.

Gene duplication

A process that creates extra copies of genes; a key source of new genetic material for evolution.

Allele frequency

The proportion of a particular allele among all alleles for a gene in a population.

Genotype frequency

The proportion of individuals with a given genotype in a population.

Gene pool

All copies of every allele at all genes in all members of a population.

Hardy-Weinberg equilibrium

Expected genetic makeup in a population that is not evolving; p^2 + 2pq + q^2 = 1.

p

Frequency of the first (often dominant) allele in a two-allele system.

q

Frequency of the second allele in a two-allele system.

p^2

Frequency of homozygous dominant genotypes (for a two-allele system).

2pq

Frequency of heterozygous genotypes (for a two-allele system).

q^2

Frequency of homozygous recessive genotypes (for a two-allele system).

Random mating

Mating occurring without regard to genotype frequencies; no population structure.

Hardy-Weinberg conditions

Five conditions for equilibrium: random mating, no natural selection, very large population size, no gene flow, no mutation.

Founder effect

A type of genetic drift where a small group colonizes a new area; allele frequencies differ from the original population.

Bottleneck effect

Genetic drift that occurs after a drastic reduction in population size, altering the gene pool.

Genetic drift effects

Significant in small populations; can cause random allele frequency changes, loss of variation, and fixation of harmful alleles.

Directional selection

Natural selection that favors one end of the phenotypic range, shifting the population mean.

Disruptive selection

Natural selection that favors extreme phenotypes over intermediate ones.

Stabilizing selection

Natural selection that favors average phenotypes, reducing variation.

Sexual selection

A form of natural selection where traits improve an individual's mating success; often leads to sexual dimorphism.

Good genes hypothesis

Females choose mates with traits indicative of genetic quality or health.

Heterozygote advantage

When heterozygotes have higher fitness than either homozygote, maintaining multiple alleles.

Sickle cell and malaria (heterozygote advantage)

Heterozygotes for the sickle-cell allele have malaria resistance, increasing allele frequency in malaria areas.

Polydactyly

Having extra toes or fingers; high frequency in Key West due to a founder effect rather than advantage.

Fitness

An individual's overall reproductive success compared to others.

Relative fitness

Fitness of a genotype or phenotype relative to the most successful genotype.

Adaptive evolution

Evolution driven by natural selection resulting in adaptations to the environment.