Evolutionary Biology: Processes, Phylogenies, Genomes, and Speciation

Comprehensive vocabulary flashcards covering the processes of evolution, phylogenetic trees, molecular evolution, and speciation.

Evolution

The change in the genetic composition of a population over time.

Natural Selection

The evolutionary process by which individuals best adapted to their environment survive and reproduce, driven by differential fitness of individual phenotypes within a population.

Biological Fitness

The relative survival and reproduction success of an individual compared to others in the population.

Adaptation

A heritable trait that evolved in a population through natural selection; refers both to the trait itself and to the evolutionary process that produced it.

Gene Flow

The transfer and exchange of alleles between populations through the migration of individuals or movement of gametes.

Genetic Drift

Random change in allele frequencies over time, which exerts a significantly stronger effect in small populations than in large ones.

Population Bottleneck

A large decrease in population size caused by a random mortality event where only a few individuals survive, resulting in a random loss of genetic diversity.

Founder Effect

The establishment of a new population by a small group of individuals, resulting in a random sample of alleles from the original parent population.

Sexual Selection

A form of selection that occurs when individuals of one sex mate preferentially with particular individuals of another sex rather than at random.

Hardy–Weinberg Equilibrium

A principle stating that allele and genotype frequencies remain constant across generations in the absence of evolution ($p + q = 1$ and $p^2 + 2pq + q^2 = 1$), assuming no mutation, no selection, no gene flow, random mating, and an infinite population size.

Stabilizing Selection

A mode of natural selection where individuals with intermediate or mean phenotypes have higher fitness than individuals with extreme phenotypes.

Directional Selection

A mode of natural selection where an extreme phenotype has higher fitness than the average phenotype, causing a directional shift in the population mean.

Disruptive Selection

A mode of natural selection where both extreme phenotypes have higher fitness than intermediate phenotypes.

Heterozygote Advantage

A condition in which heterozygous individuals have higher fitness than either homozygous genotype, maintaining genetic variation in a population.

Evolutionary Trade-off

A constraint in which a trait that improves fitness in one environmental context reduces fitness in another.

Binomial Nomenclature

The hierarchical naming system created by Carolus Linnaeus where each species is assigned a two-part Latin name consisting of a capitalized genus followed by a lowercase species epithet.

Phylogeny

The evolutionary history of a group of organisms.

Phylogenetic Tree

A diagrammatic hypothesis illustrating evolutionary relationships and lineage divergences among species, populations, or genes.

Node (Phylogenetic)

A branching point on a phylogenetic tree representing an ancestral lineage dividing into descendant lineages.

Sister Taxa

Two phylogenetic lineages that emerge from the same immediate common ancestor node and are each other's closest relatives.

Monophyletic Group

A group consisting of a common ancestor and all of its descendants; also known as a clade.

Paraphyletic Group

A taxonomic group that includes a common ancestor and some, but not all, of its descendants.

Polyphyletic Group

A group of organisms that does not include the common ancestor shared by all of its members.

Plesiomorphy

An ancestral trait present in the ancestral lineage of a given clade.

Synapomorphy

A derived trait that arose in a common ancestor and is shared by the descendant members of a clade.

Homoplasy

A shared trait among species that evolved independently through convergent evolution or an evolutionary reversal rather than through common descent.

Parsimony Principle

The guiding principle in phylogenetics stating that the best phylogenetic tree is the one that requires the fewest evolutionary changes.

Molecular Clock

A method that utilizes the constant rate of genetic mutations in DNA or protein sequences to estimate the timing of evolutionary divergence events.

Homologous Sequence

A DNA or protein sequence shared among different species that originated from a common ancestral sequence.

Synonymous Substitution

A nucleotide substitution in a protein-coding sequence that does not alter the specified amino acid, remaining neutral to natural selection.

Nonsynonymous Substitution

A nucleotide substitution in a protein-coding gene that changes the amino acid in the resulting protein, potentially altering protein function.

Purifying Selection (Molecular)

Natural selection that removes harmful nonsynonymous mutations from a population, resulting in a substitution ratio of $dN/dS < 1$.

Positive Selection (Molecular)

Natural selection that favors beneficial nonsynonymous mutations, driving them toward fixation and resulting in a substitution ratio of $dN/dS > 1$.

Pseudogene

A duplicate copy of a gene that has accumulated inactivating mutations and lost its original protein-coding function.

Lateral Gene Transfer

The direct transfer of genetic material between distinct species rather than through vertical parent-to-offspring descent.

Morphological Species Concept

A framework that defines a species as a group of organisms that are morphologically distinct from other groups based on structural characteristics.

Biological Species Concept

A framework that defines a species as a group of interbreeding natural populations that are reproductively isolated from other groups and share a distinct gene pool.

Dobzhansky–Muller Model

A genetic model explaining that alleles arising and fixing independently at different loci in geographically isolated populations become incompatible and cause low fitness or inviability when combined in hybrids.

Allopatric Speciation

Speciation that occurs when an ancestral population is divided by a physical geographic barrier, preventing gene flow and allowing independent divergence.

Sympatric Speciation

Speciation that occurs without physical barriers, where reproductive isolation develops among segments of a population inhabiting the same geographic area.

Autopolyploidy

A form of polyploidy resulting from the duplication of chromosomes within a single species, often caused by meiotic nondisjunction.

Allopolyploidy

A form of polyploidy that occurs when genomes from two distinct species combine during hybridization followed by chromosome duplication.

Reinforcement (Speciation)

An outcome of secondary contact in which natural selection against low-fitness hybrids favors the evolution of stronger prezygotic isolating barriers.

Prezygotic Isolating Mechanisms

Reproductive barriers that prevent mating or fertilization from occurring between species, including mechanical, temporal, behavioral, habitat, and gametic isolation.

Postzygotic Isolating Mechanisms

Reproductive barriers that operate after fertilization, including low hybrid zygote viability, low hybrid adult viability, and hybrid infertility.

Adaptive Radiation

A rapid burst of speciation and phenotypic diversification from a common ancestral lineage into a wide array of species that occupy diverse ecological niches.

Heterochrony

An evolutionary modification in the developmental rate or timing of anatomical events, which can produce novel morphological structures and drive speciation.