Evolutionary Biology: Mechanisms, Molecular Evolution, and Adaptation

Comprehensive vocabulary flashcards covering the raw materials of evolution, genetics, population genetics, molecular evolution, phylogenetics, and adaptations.

Evolution

A change in gene or allele frequencies within a population over time across generations.

Natural Selection

The evolutionary process by which individuals better adapted to their environment preferentially survive and reproduce, leaving more offspring with their traits to future generations through non-random, differential reproduction.

Genetic Drift

Evolution arising from random sampling error that causes allele frequencies in a population to fluctuate from one generation to another, often reducing genetic variation.

Gene Flow

The movement and spread of genes across the geographic range of a population or from one population into another.

Codon

A three-letter nucleotide sequence in DNA or RNA that signals the start of a gene (AUG), encodes a specific amino acid, or marks the termination of translation (STOP codons UAA, UAG, UGA).

Locus

A specific, defined physical location or base sequence on a DNA molecule, which can refer to a functional gene or any arbitrary non-coding sequence.

Allele

One of two or more alternative variants of a gene found at the same genetic locus that differ in DNA sequence and produce distinct traits.

Law of Segregation

Mendel's principle stating that pairs of alleles separate during gamete formation so that traits remain distinct and maintained in offspring rather than blending together.

Law of Independent Assortment

Mendel's principle stating that alleles of different genes assort independently of one another during the formation of gametes.

Gene Expression

The process determining whether a gene is actively transcribed and translated to produce a functional product, such as a protein or RNA.

Genome

The entirety of the DNA present within an organism, including both protein-coding genes and non-coding sequences.

Pseudogene

A non-functional, disabled DNA sequence that was formerly used as an active gene in ancestral organisms but accumulated disabling mutations.

Point Mutation

A mutation involving the substitution or change of a single nucleotide base in a DNA sequence for another.

Frameshift Mutation

A genetic mutation caused by the insertion or deletion of nucleotides in numbers not divisible by three, which alters the triplet reading frame of all subsequent codons.

Gene Duplication

A mutational mechanism in which a segment of DNA is copied, allowing the ancestral gene to maintain its original function while the duplicate copy is free to evolve a novel function.

Somatic Mutation

A mutation occurring in non-reproductive body cells that affects only the individual organism in which it arises and cannot be transmitted to offspring.

Germ-line Mutation

A mutation arising in reproductive cells (gametes) that can be inherited by offspring and is directly relevant to evolutionary change.

Two-hit Hypothesis

The model proposing that certain cancers develop through a combination of an inherited germ-line mutation and subsequent acquired somatic mutations in the same cell lineage.

Horizontal Gene Transfer

The movement of genetic material directly between non-parent-offspring individuals across lineages, commonly observed among prokaryotes.

Population Genetics

The branch of evolutionary biology that studies the distribution of alleles within populations and the mechanisms that cause allele frequencies to change over time.

Hardy-Weinberg Equilibrium

A null model stating that allele and genotype frequencies remain constant across generations in an infinitely large, randomly mating population free from selection, mutation, and migration, following the equation $p^2 + 2pq + q^2 = 1$.

Bottleneck Effect

A sharp reduction in population size caused by an environmental catastrophe or hunting, which drastically reduces genetic diversity and amplifies the impact of genetic drift.

Founder Effect

A form of genetic bottleneck occurring when a small subset of individuals leaves a larger ancestral population to establish a new colony, carrying only a subset of the source genetic diversity.

Relative Fitness

The reproductive success and genetic contribution of an individual, genotype, or phenotype to the next generation relative to other individuals in the population.

Mutation-Selection Balance

An equilibrium reached when the rate at which deleterious mutations are introduced into a population equals the rate at which negative selection eliminates them.

Balancing Selection

A type of natural selection that actively maintains multiple alleles at a locus within a population rather than driving one allele to fixation.

Directional Selection

A mode of natural selection that favors individuals at one extreme of a phenotypic distribution, causing the population mean for the trait to shift over time.

Stabilizing Selection

A mode of natural selection that favors intermediate phenotypes near the population mean while selecting against individuals with extreme trait values, narrowing phenotypic variation.

Disruptive Selection

A mode of natural selection that favors individuals at both tails of a phenotypic distribution over intermediate phenotypes, which can divide a single distribution curve into two peaks.

Anthropogenic Evolution

Evolutionary changes in allele frequencies and organismal traits driven directly or indirectly by human activities, including artificial selection, commercial harvesting, hunting, and habitat alteration.

Molecular Phylogeny

The reconstruction of evolutionary histories and ancestral relationships among species based on comparative alignments of homologous DNA, RNA, or amino acid sequences.

Coalescence

The process of tracing alleles or gene lineages backward in time to identify the common ancestral gene copy from which all extant alleles originated.

Incomplete Lineage Sorting

A scenario where the branching topology of a gene tree fails to match the branching history of the species tree, often because ancestral polymorphism persists through rapid speciation events.

Out-of-Africa Hypothesis

The model of human evolution stating that all modern Homo sapiens populations originated from a recent African ancestor that expanded globally and replaced other hominin species.

Neutral Evolution

Motoo Kimura's theoretical framework proposing that the majority of molecular variations across genomes are neutral and that their fixation or loss is governed by genetic drift rather than natural selection.

Molecular Clock

A method that utilizes the steady, predictable accumulation of neutral mutations over time to estimate the timing of evolutionary divergences between lineages.

Synonymous Substitution

A nucleotide base substitution in a coding sequence (often at the third codon position) that alters the codon without altering the resulting amino acid, making the mutation functionally neutral.

Viral Reassortment

The exchange of genetic genome segments between distinct viral strains coinfecting the same host cell, resulting in novel hybrid viruses such as H1N1 influenza.

Adaptation

A heritable, functional phenotypic trait produced by natural selection that enhances an organism's survival and reproductive fitness in its environment.

Vestigial Structure

An inherited anatomical feature that served an adaptive function in an ancestral species but has evolved to become non-functional in descendants due to changing environmental selective pressures.

Exaptation

The evolutionary co-option of an existing trait or structure that originally evolved for one function to serve a completely new biological purpose.

Regulatory Network

A coordinated system of interacting genes, transcription factors, and repressors that governs the spatial and temporal patterns of gene expression in an organism.

Promiscuous Proteins

Proteins capable of performing minor secondary functions or catalyzing alternative reactions in addition to their primary evolutionary biological task.

Gene Recruitment

The evolutionary co-option of an existing gene for a novel function through mutations that change its regulatory elements, modifying when and where the gene is expressed.

Complex Adaptation

An integrated phenotypic system governed by multiple interacting genes and anatomical components that evolves in a step-by-step manner rather than appearing all at once.

Scaffolding Model

A model of complex adaptation evolution in which intermediate structures or functions present during early evolutionary stages are subsequently lost once the final complex structure is established.

Incremental Additions Model

A model describing the origin of complex adaptations where small, initially optional improvements or changes accumulate sequentially and eventually become essential.

Hox Genes

A highly conserved suite of regulatory genes in the genetic toolkit of Bilateria that controls the anterior-posterior patterning and body plan identity during embryonic development.

Opsins

G-protein coupled receptor proteins in photoreceptor cells that capture photons of light, undergoing conformational changes that generate electrical signals sent to the brain.

Crystallins

Optically clear, stable proteins—originally recruited from heat shock proteins—that pack tightly to form lenses that focus light in animal eyes.

Phylogenetic Inertia

The evolutionary constraint wherein modern adaptations are limited and biased by the ancestral anatomical, developmental, and genetic structures inherited by a lineage.

Antagonistic Pleiotropy

An evolutionary constraint occurring when a single gene influences multiple phenotypic traits, where one effect increases fitness while another simultaneous effect decreases fitness.

Convergent Evolution

The independent evolution of similar anatomical or physiological traits in distinct, distantly related lineages experiencing similar environmental selective pressures.