The Evolution of Populations Vocabulary

Vocabulary flashcards based on lecture notes for Chapter 21: The Evolution of Populations, covering mechanisms of evolution, Hardy-Weinberg equilibrium, and modes of selection.

Microevolution

The smallest unit of evolution, defined as a change in allele frequencies in a population over generations.

Genetic variation

Differences in the composition of genes or other $DNA$ sequences among individuals, which acts as a prerequisite for evolution by natural selection.

Phenotype

The physical or behavioral appearance of an organism, resulting from the interaction of its genotype and the environment.

Genotype

The genetic composition, specifically the alleles, of an individual that correlates to its phenotype.

Mutation

A change in the nucleotide sequence of an organism’s $DNA$ that can produce new alleles and genes.

Gene variability

Genetic variation at the whole gene level, often measured as the average percent of loci that are heterozygous.

Nucleotide variability

Genetic variation measured at the molecular level of $DNA$; most of these differences occur in noncoding regions (introns).

Population

A group of individuals that live in the same area and interbreed, producing fertile offspring.

Gene pool

The collection of all alleles for all loci in a population.

Hardy-Weinberg equilibrium

A state where allele and genotype frequencies in a gene pool remain constant from generation to generation in a population that is not evolving.

Hardy-Weinberg equation

A mathematical formula used to describe the expected genetic makeup of a non-evolving population at a specific locus: $p^2 + 2pq + q^2 = 1$.

$p$ and $q$

Variables used in the Hardy-Weinberg equation to represent the relative frequencies of only two possible alleles at a particular locus, where $p + q = 1$.

$p^2$ and $q^2$

Variables in the Hardy-Weinberg equation representing the frequencies of homozygous genotypes.

$$2pq$$

The variable in the Hardy-Weinberg equation representing the frequency of the heterozygous genotype.

Natural selection

The only mechanism of evolution that consistently causes adaptive evolution by favoring alleles that improve reproductive success.

Genetic drift

A process in which allele frequencies fluctuate randomly from one generation to the next due to chance, especially in small populations.

Gene flow

The movement of alleles among populations through the transfer of fertile individuals or gametes; it tends to reduce genetic variation between populations.

Founder event

A type of genetic drift that occurs when only a few individuals start a new population, potentially causing different allele frequencies than the source population.

Bottleneck effect

A sudden reduction in population size due to an environmental change, resulting in a gene pool that may no longer reflect the original population.

Relative 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 natural selection that occurs when conditions favor individuals at one end of the phenotypic range.

Stabilizing selection

A mode of natural selection that occurs when conditions favor intermediate variants and act against extreme phenotypes.

Disruptive selection

A mode of natural selection that favors individuals at both ends of the phenotypic range over the intermediate variants.

Balancing selection

A type of natural selection that maintains stable frequencies of two or more phenotypic forms in a population.

Heterozygote advantage

A form of balancing selection that occurs when heterozygous individuals have greater fitness than both kinds of homozygotes, such as individuals carrying the sickle-cell allele in malaria-prone areas.

Frequency-dependent selection

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

Sexual selection

Natural selection for mating success, which can result in traits that increase reproductive access but not necessarily survivability.

Sexual dimorphism

Marked differences between the sexes in secondary sexual characteristics.

Intra-sexual selection

Competition within one sex (usually males) for access to the other sex.

Inter-sexual selection

Also known as mate choice, it occurs when individuals of one sex (usually females) are choosy in selecting their mates.

Anisogamy

A form of sexual reproduction involving the union or fusion of two dissimilar gametes, typically many small sperm from males and one large egg from females.