Chapter 20: Genes Within Populations Vocabulary Flashcards

Vocabulary flashcards covering key definitions and mechanisms of population genetics, evolution, Hardy–Weinberg equilibrium, and natural selection.

Genetic Variation

Differences in alleles of genes (genotype) found within individuals in a population.

Evolution

A increase or decrease in frequency of alleles.

The historical record or outcome of change through time, described by Charles Darwin as descent with modification.

Natural Selection

The process in which environmental conditions determine which individuals produce the most offspring based on favored alleles.

Allele

Alternate forms of a gene, such as those determining blood type or hair color.

Genotype

All the alleles present in an individual for a specific gene or set of genes.

Phenotype

The visible or physical appearance of a trait in an individual.

Dominant Allele

An allele that masks the expression of another allele and is expressed in both homozygous and heterozygous individuals.

Recessive Allele

An allele whose expression is masked by a dominant allele and is expressed only in homozygous individuals.

Single Nucleotide Polymorphism (SNP)

A single base difference between individuals in a population present at a frequency greater than $1\,\%$.

Hardy–Weinberg Principle

The principle stating that genotype and allele frequencies in a population remain constant across generations if no mutation occurs, no gene flow occurs, random mating occurs, population size is very large, and no selection occurs.

Hardy–Weinberg Allele Frequency Equation

The equation $p + q = 1$, where $p$ is the frequency of the dominant allele and $q$ is the frequency of the recessive allele.

Hardy–Weinberg Genotype Frequency Equation

The equation $p^2 + 2pq + q^2 = 1$, where $p^2$ is the homozygous dominant genotype frequency, $2pq$ is the heterozygous genotype frequency, and $q^2$ is the homozygous recessive genotype frequency.

Gene Flow

The movement of alleles from one population to another through the movement of individuals, gametes, or seeds.

Assortative Mating

A form of nonrandom mating where phenotypically similar individuals mate more frequently, increasing the proportion of homozygous individuals.

Disassortative Mating

A form of nonrandom mating where phenotypically different individuals mate more frequently than expected by chance, producing an excess of heterozygotes.

Genetic Drift

Random fluctuations in allele frequencies over time, having the strongest effect in small populations.

Founder Effect

A form of genetic drift that occurs when one or a few individuals disperse and establish a new, isolated population carrying only a subset of the original population's alleles.

Bottleneck Effect

A drastic reduction in population size caused by environmental events or disasters, leading to a loss of genetic variability in the surviving population.

Artificial Selection

A selection process in which a breeder deliberately chooses individuals with desired characteristics for reproduction.

Fitness

A measure of relative reproductive success defined by the number of surviving offspring produced by a phenotype in the next generation.

Parental Investment

The time and energy each sex invests in producing and rearing offspring.

Intrasexual Selection

Competitive interactions between members of the same sex (usually males) for the opportunity to mate.

Intersexual Selection

Mate choice, where individuals of one sex (usually females) choose mates based on specific physical traits or qualities.

Sexual Dimorphism

Morphological differences between males and females of the same species, often resulting from selection for competitive or attractive traits.

Negative Frequency-Dependent Selection

A form of selection where rare phenotypes are favored over common ones, maintaining genetic variation in a population.

Positive Frequency-Dependent Selection

A form of selection where common phenotypes are favored over rare ones, which tends to eliminate genetic variation.

Oscillating Selection

A form of selection where the favored phenotype shifts over time as environmental conditions change, maintaining genetic variation.

Heterozygote Advantage

A phenomenon where heterozygous individuals exhibit higher fitness than either homozygous genotype, maintaining both alleles in the population.

Disruptive Selection

A mode of natural selection that acts to eliminate intermediate phenotypes, favoring extreme phenotypes at both ends.

Directional Selection

A mode of natural selection that acts to eliminate phenotypes at one extreme of the spectrum, shifting the population mean toward the other extreme.

Stabilizing Selection

A mode of natural selection that eliminates both phenotypic extremes, increasing the frequency of intermediate phenotypes.

Electrophoresis

A technique used to assay genetic variation by separating DNA into fragments based on size.