Introduction to Evolution and Population Genetics Vocabulary

Vocabulary practice flashcards covering fundamental concepts, mechanisms, and key figures in evolutionary biology, genetics, and selection.

Theory of Endosymbiosis

The theory proposed by Lynn Margulis stating that eukaryotic organelles, such as mitochondria, originated from the fusion of two distinct evolutionary lineages.

Principle of Uniformitarianism

A geological principle championed by Charles Lyell stating that present-day geological processes (such as erosion, earthquakes, and volcanoes) can explain the historical features of the Earth.

Inheritance of Acquired Characteristics

Jean-Baptiste de Lamarck's proposed mechanism of evolutionary change, which hypothesized that physiological changes acquired by an individual during its lifetime can be passed on to its offspring.

Evolution

The change in inherited traits of a population across successive generations, ultimately leading to the transformation of species through time.

Biodiversity

The diversity of life on Earth, encompassing the total number and kinds of living organisms in a given area.

Adaptation (Noun)

Any heritable trait that enhances an organism's ability to survive or reproduce in a specific environment.

Homology

The similarity of structural, developmental, or genetic characteristics among different species resulting from shared inheritance from a common ancestor.

Vestigial Structures

Reduced or functionless features inherited from an ancestor that are homologous to fully functional structures found in related species.

Convergent Evolution

The independent evolution of similar traits or functional structures in distantly related lineages as a result of adaptation to similar ecological environments.

Microevolution

Evolutionary patterns and processes occurring within a single species or population over short timescales.

Macroevolution

Evolutionary patterns and processes observed among different species over long geological timescales.

Genotype

The specific genetic constitution of an organism, defined in relation to a specific gene locus or combination of gene loci.

Phenotype

The observable physical, physiological, or behavioral traits of an organism resulting from its genotype and environmental interactions.

Genome

The entirety of an organism's DNA, including both coding genes and non-coding sequences.

Point Mutation

A type of mutation involving a single base pair substitution in the DNA sequence.

Indel

A mutation caused by the insertion or deletion of one or more nucleotide base pairs in a DNA sequence.

Silent Mutation

A nucleotide substitution that alters a codon without changing the encoded amino acid sequence of a protein.

Missense Mutation

A nucleotide substitution that alters a codon, resulting in the replacement of one amino acid with a different amino acid in a protein sequence.

Nonsense Mutation

A nucleotide substitution that alters an amino acid codon into a premature stop codon, terminating protein translation.

Heterozygosity ($H$)

The fraction of individuals in a population that carry two different alleles at a given locus, averaged across gene loci.

Polymorphism ($P$)

The proportion of gene loci in a population that possess two or more distinct alleles.

Haplotype

A specific set of linked alleles on a single chromosome that are inherited together from a single parent.

Genetic Drift

Random fluctuations in allele frequencies in a population from generation to generation due to chance sampling events, having a larger effect in small populations.

Fixation

The state in which a previously polymorphic locus becomes monomorphic because all alternative alleles have been lost, leaving only a single allele in the population.

Purifying Selection

A form of natural selection (also known as negative selection) that reduces genetic variation by eliminating deleterious mutations from a population.

Directional Selection

A form of natural selection that shifts the population mean by favoring individuals expressing one extreme phenotype over others.

Stabilizing Selection

A type of natural selection that reduces phenotypic variation by favoring intermediate phenotypes while selecting against extreme trait values.

Disruptive Selection

A mode of natural selection that favors individuals at both phenotypic extremes while selecting against intermediate phenotypes, leading to trait divergence.

Balancing Selection

Natural selection that maintains multiple alleles at a locus over generations, through mechanisms such as heterozygote advantage or frequency-dependent selection.

Neutral Theory of Molecular Evolution

Motoo Kimura's hypothesis stating that the vast majority of evolutionary changes at the molecular level are caused by genetic drift acting on selectively neutral mutations.

Selective Sweep

The rapid increase in frequency and fixation of a beneficial allele due to strong positive selection, causing closely linked neutral alleles to "hitchhike" along with it and reducing nearby genetic diversity.

Parthenogenesis

A form of asexual reproduction in which an unfertilized egg cell develops directly into a new individual.

Dioecious

Having male and female reproductive structures borne on separate individual organisms.

Hermaphrodite

An organism that possesses both male and female functional reproductive organs within the same individual.

Two-Fold Cost of Meiosis

The 50% transmission reduction incurred by sexual females compared to asexual females, because a sexual female transmits only half of her alleles to each offspring.

Tangled Bank Hypothesis

A theory explaining the advantage of sexual reproduction, positing that producing genetically diverse offspring allows better exploitation of spatially heterogeneous habitats.

Red Queen Hypothesis

A theory proposing that sexual reproduction provides an evolutionary advantage in temporally heterogeneous environments, enabling organisms to continuously adapt to evolving parasites, pathogens, or competitors.

Inbreeding Depression

The reduction in fitness, viability, or reproductive output of offspring produced by mating between close genetic relatives compared to outcrossed matings.

Anisogamy

A sexual reproduction system involving the fusion of two morphologically distinct gametes differing significantly in size (e.g., large eggs and small sperm).

Intrasexual Selection

A mechanism of sexual selection involving direct competition between individuals of the same sex (typically males) for access to mates or fertilization opportunities.

Intersexual Selection

A mechanism of sexual selection (female choice) in which individuals of one sex (typically females) choose mates based on specific display traits or courtship signals.

Runaway Selection

A process in which a genetic correlation between female preference and a male trait drives the co-evolution and extreme exaggeration of male ornamental traits (also known as the "sexy sons" hypothesis).

Sensory Bias Hypothesis

A theory suggesting that female preference for a male trait evolves first due to pre-existing sensory biases originally used for other functions (such as foraging), which males later exploit with courtship displays.

Population (Ecological Definition)

A group of individuals belonging to a single species occupying a given geographic area at the same time.

Gene Flow

The movement and incorporation of alleles between distinct populations through the dispersal of individuals or gametes.

Neutral Genetic Markers

Polymorphic genetic variants that are not direct targets of selection, used by researchers to infer non-selective processes like gene flow and genetic drift.

Population Bottleneck

A sharp, temporary reduction in population abundance that results in a severe loss of genetic diversity in subsequent generations.

Founder Event

The colonization of a new location by a small number of individuals carrying only a subset of the genetic variation present in the source population.

Isolation by Distance

A spatial pattern in which genetic differentiation between populations increases with geographic distance due to restricted dispersal.

Reciprocal Transplant Experiment

An experimental technique of growing different genotypes in shared and native environments to distinguish genetic local adaptation from environmental plasticity.

Phenotypic Plasticity

The ability of a single genotype to produce different morphological, physiological, or behavioral traits in response to varying environmental conditions.

Selective Pressure on Skin Pigmentation in High-UV Regions

Strong purifying selection on genes like MC1R to prevent folate degradation in environments with high UV exposure.

Neanderthal Introgression in Modern Humans

The persistence of approximately $2\%$ Neanderthal-derived DNA in non-African human genomes resulting from ancient interbreeding events.

Population Thinking

An evolutionary perspective formulated by Ernst Mayr that rejects ideal typological archetypes and instead views individual phenotypic and genetic variation within a group as the primary raw material for evolutionary change.

Descent with Modification

The overarching pattern of evolution recognized by Charles Darwin, stating that all extant species originated from shared ancestral lineages and accumulated changes across successive generations.

Natural Selection (Ecological Mechanism)

The evolutionary process wherein individuals possessing advantageous heritable traits achieve greater reproductive success than individuals lacking those traits, driving adaptation to local environments.

Speciation Continuum

The gradual, potentially reversible transition of biological lineages from panmictic populations, through partially differentiated ecotypes with ongoing gene flow, to fully isolated, distinct reproductive units.

Ring Species

A geographic distribution in which a chain of interbreeding, adjacent populations expands around an environmental barrier until the terminal populations meet in sympatry, unable to interbreed.

Ecological Speciation

The evolution of reproductive barriers between diverging populations driven by divergent natural selection as organisms adapt to distinct ecological niches, food sources, or host plants.

Geographic Pattern of Succession

The biogeographic observation in paleontology that fossil forms discovered in a particular geographic region closely resemble the living, extant species inhabiting that same area.

Transitional Fossil

A preserved specimen that exhibits a mosaic of diagnostic morphological traits found in both an ancestral taxon and its derived descendants (such as Archaeopteryx linking non-avian dinosaurs to modern birds).

Analogy (Homoplasy)

Superficial functional and morphological similarity between organisms arising independently via convergent evolution rather than through common evolutionary descent.

Developmental Vestige

An ancestral structure that initiates formation during embryonic development but is aborted or degrades prior to the adult stage, such as the aborted eye development in adult blind cavefish (Astyanax mexicanus).

Processed Pseudogene

A nonfunctional DNA sequence created when processed, intronless messenger RNA is reverse-transcribed and reintegrated into the nuclear genome, evolving neutrally without the influence of natural selection.

Consilience

The agreement and mutual support of multiple independent lines of scientific inquiry—such as radiometric dating, stratigraphy, and molecular phylogenetics—converging on a single evolutionary conclusion.

Radiometric Age of Earth

The approximate age of Earth established through isotopic decay analyses of geological materials, determined to be $4.54\text{ billion years}$.

Oldest Direct Fossil Evidence of Life

Preserved fossilized cyanobacteria discovered in Australian rock formations dating to approximately $3.5\text{ billion years}$ ago.

Tiktaalik roseae

A transitional fossil discovered on Ellesmere Island dated to between $350$ and $425\text{ million years}$ ago, displaying fish-like scales alongside tetrapod-like wrists and limb bones that illustrate the vertebrate transition onto land.

Belyaev and Trut Fox Domestication Experiment

A long-term breeding study demonstrating that artificial selection solely for tameness in silver foxes (Vulpes vulpes) rapidly produced behavioral changes alongside morphological changes such as floppy ears, curly tails, and coat color shifts within a few decades.

Darwin's Four Postulates

The conditions required for evolution by natural selection: (1) individuals in a population vary in traits, (2) some trait variation is heritable, (3) more offspring are produced than can survive, and (4) survival and reproduction are non-random with respect to those traits.

Parent-Offspring Regression

A quantitative genetics method where offspring trait values are plotted against the average trait values of their parents; the slope of the resulting regression line provides an estimate of heritability.

Heritability

The proportion of total phenotypic variation among individuals in a population that is attributable to genetic differences rather than environmental effects.

Struggle for Existence

The competition among individuals for limited resources arising when population growth outpaces available resources, a concept Charles Darwin adopted from economist Thomas Malthus.

Biological Fitness

A relative measure of reproductive success, defined as the average contribution of an individual with a specific phenotype to the gene pool of the next generation in a given environment.

Distinction Between Natural Selection and Evolution

The difference between an ecological process occurring within a single generation through differential survival and reproduction of individuals, and the resulting transgenerational change in allele frequencies or trait distributions across the population.

1977 Daphne Major Selection Event

A severe drought that caused an over $85\%$ population crash in Geospiza fortis, leading to directional selection that favored individuals with larger, deeper beaks capable of opening large, hard seeds.

Poecilia mexicana (Cave Molly)

A species of livebearing fish used to examine natural selection and divergence by comparing surface-dwelling populations with geographically isolated populations living in lightless subterranean habitats like Cueva Luna Azufre.

Modern Synthesis

The historical integration of Mendelian genetics and Darwinian natural selection into a unified theoretical framework that established population genetics as the foundation of evolutionary biology.

Genotype-Phenotype Gap

The scientific challenge of identifying and mapping the complex, many-to-many molecular interactions and regulatory networks that translate genomic sequence variation into emergent organismal traits.

MicroRNAs (miRNAs)

Short, non-coding RNA molecules that regulate gene expression post-transcriptionally by binding complementary messenger RNA sequences to trigger transcript degradation and arrest translation.

Chromosomal Inversion

A structural mutation caused by two double-strand breaks where an internal segment flips orientation before rejoining, mechanically suppressing crossing over and recombination across the region in heterozygotes.

Unequal Crossing-Over

A meiotic recombination error resulting from the misalignment of homologous chromosomes, producing one recombinant chromatid with a duplicated gene segment and another with a deletion.

Gene Dosage Effect

A physiological or developmental disturbance occurring when a change in the physical copy number of a gene disproportionately alters the concentration of its encoded protein within calibrated cellular networks.

Hardy-Weinberg Principle

A foundational null model stating that allele and genotype frequencies in a diploid population remain constant across generations when evolutionary forces such as mutation, selection, genetic drift, gene flow, and non-random mating are absent.

Selection Coefficient ($s$)

A quantitative parameter describing the proportional difference in relative fitness between a given genotype and an assigned reference genotype.

Positive Frequency-Dependent Selection

A selective mode where the fitness of a phenotype increases as its frequency in the population rises, driving common morphs to fixation (such as shared warning coloration in toxic Heliconius butterflies).

Negative Frequency-Dependent Selection

A selective mode where the fitness of a phenotype decreases as it becomes more abundant, conferring a reproductive advantage to rare variants and actively preserving genetic polymorphism (such as color morphs in the deceptive orchid Dactylorhiza sambucina).

Mutation-Selection Balance

An equilibrium state where the rate of elimination of a deleterious allele by natural selection matches its rate of reintroduction via recurrent mutation, yielding an equilibrium frequency of $q = \sqrt{\frac{\mu}{s}}$ for recessive deleterious alleles.

Effective Population Size ($N_e$)

The number of actively breeding individuals in an idealized population that would experience the same rate of genetic drift, inbreeding, or loss of heterozygosity as the observed census population.

One-Island Migration Model

A population genetic framework describing unidirectional gene flow from a large mainland donor to a small recipient island population, causing recipient allele frequencies to homogenize toward donor frequencies over successive generations.

Genetic Rescue

The artificial introduction of immigrants or outbred genetic material into small, isolated populations to alleviate inbreeding depression, restore heterozygosity, and boost population viability.

Coefficient of Inbreeding ($F$)

The probability that two homologous alleles at a given locus within an individual are identical by descent due to shared ancestry between their parents.