BIO120: Adaptation and Biodiversity - Evolutionary Biology and Ecology

Vocabulary practice flashcards for introductory evolution, genetics, ecology, and natural selection (BIO120).

Homology

The similarity of characteristics between two or more species that is due to inheritance from a common ancestor (for example, the shared structural arrangement of bones across vertebrate forelimbs or mouthparts across different insects).

Vestigial Structures

Features inherited from an ancestor that have become reduced in morphology and function compared to functional homologous structures in related species, such as human ear muscles, the appendix, the tailbone, goosebumps, and the reduced wings of the Galápagos flightless cormorant.

Tiktaalik roseae

A 375-million-year-old transitional fossil discovered on Ellesmere Island, Nunavut, documenting the fish-to-tetrapod transition as fins evolved into limbs.

Convergent Evolution

The independent evolution of similar traits in distantly related lineages driven by natural selection in similar ecological environments, such as Australian marsupial potoroos and European placental rabbits, or ecologically matched Caribbean Anolis lizard ecomorphs in Cuba and Hispaniola.

Teosinte

The wild grass ancestor of modern maize (corn), illustrating the substantial morphological and genetic divergence that can be produced across generations through artificial selection.

Genotype

The genetic constitution of an individual organism, defined in relation to a specific gene or combination of gene loci specifying both alleles in diploid organisms (such as $Aa$ or $AaBB$).

Phenotype

The observable physical, physiological, or biochemical traits of an organism resulting from its genotype and environmental interactions (such as size, fur color, enzyme activity, or mRNA expression levels).

Genome

The entirety of an organism's DNA, encompassing both protein-coding genes and non-coding regions (excluding organellar genomes such as those in mitochondria or chloroplasts).

Mutation

A stable change in the DNA sequence that serves as the ultimate source of genetic variation; mutations arise inevitably due to replication errors, occur randomly with respect to their fitness effects, and can be neutral, deleterious, or beneficial.

Independent Assortment

The random assortment of maternal and paternal homologous chromosome pairs during meiosis, generating $2^n$ possible gamete combinations (where $n$ is the haploid chromosome number), which equates to $8.4 \times 10^6$ gamete combinations in humans ($n=23$) and $3.4 \times 10^{153}$ in the fern Ophioglossum petiolatum ($n=510$).

Recombination

The reciprocal exchange of genetic material between homologous non-sister chromatids during meiosis, breaking linkage between loci to create novel combinations of existing alleles (new haplotypes).

G6PD Deficiency

The most common human enzyme deficiency, caused by two amino acid replacement mutations in glucose-6-phosphate dehydrogenase that produce the $A^-$ allele, causing severe anemia while simultaneously conferring resistance against malaria.

Particulate Inheritance

Gregor Mendel's model of heredity establishing that phenotypic traits are inherited as discrete, non-blending particles (genes), with diploid organisms carrying two alleles per locus that segregate cleanly into haploid gametes.

Quantitative Traits

Complex continuously varying phenotypic traits (such as height or weight) governed by polygenic inheritance—many underlying gene loci each contributing small effects—coupled with environmental variance.

The Evolutionary Synthesis

The integration of Darwinian natural selection with Mendelian genetics into a unified mathematical framework developed in the 1920s to 1950s by R. A. Fisher, J. B. S. Haldane, and Sewall Wright.

Ecology

The scientific study of the interactions among organisms and between organisms and their abiotic environment, governing the distribution and abundance of species as well as the structure and function of ecosystems (derived from the Greek oikos, meaning home).

Endosymbiotic Theory

The evolutionary theory championed by Lynn Margulis stating that eukaryotic organelles, such as mitochondria and chloroplasts, originated via the engulfment and mutualistic integration of ancestral free-living prokaryotes.

Population

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

Ecological Community

An assemblage of populations of different species co-occurring and interacting within a specified geographic area at a given time.

Ecosystem

The biological community of interacting organisms in conjunction with the non-living (abiotic) physical and chemical environment.

The Sixth Extinction

The modern, ongoing anthropogenic mass extinction event, characterized by sharp population declines or range contractions in approximately $32\%$ of known vertebrate species ($8{,}851$ out of $27{,}600$).

Heterozygosity ($H$)

The fraction of individuals within a population that possess two distinct alleles at a given locus, averaged across all studied gene loci.

Polymorphism ($P$)

The proportion of surveyed gene loci within a population that exhibit two or more alleles.

Haplotype

A specific set of alleles or linked genetic variants located on a single chromosome and inherited together from one parent.

Genetic Drift

Stochastic fluctuations in allele frequencies from generation to generation caused by random sampling error, exerting stronger effects in small populations and leading to loss of genetic variation over time.

Allele Fixation

The process whereby an allele reaches a frequency of $1.0$ ($100\%$) in a population, causing the locus to transition from polymorphic to completely monomorphic.

Gene Flow

The transfer of genetic alleles from one population to another via the migration of fertile individuals or gametes, increasing genetic diversity within recipient populations while reducing genetic differences between populations.

Classical School of Population Genetics

A perspective historically championed by T. H. Morgan and H. J. Muller predicting that natural populations exhibit low polymorphism and low heterozygosity, with a dominant 'wild type' genotype and negative selection purging rare, deleterious mutations (mutation-selection balance).

Balance School of Population Genetics

A perspective historically championed by E. B. Ford and Theodosius Dobzhansky predicting that natural populations harbor high levels of heterozygosity and polymorphism actively maintained by balancing selection, such as heterozygote advantage.

Allozymes

Electrophoretically distinct variants of an enzyme encoded by different alleles at the same locus, whose separation via gel electrophoresis revealed surprisingly elevated levels of genetic polymorphism in natural populations.

Neutral Theory of Molecular Evolution

Motoo Kimura's theoretical framework proposing that the great majority of molecular-level variation and evolutionary changes between species are selectively neutral—governed primarily by mutation and random genetic drift rather than positive Darwinian selection.

McDonald-Kreitman Test

A statistical test comparing the ratio of non-synonymous to synonymous fixed interspecific differences against the ratio of non-synonymous to synonymous intraspecific polymorphisms to evaluate whether molecular evolution has been driven by adaptive positive selection or neutral drift.

Darwinian Fitness

The relative genetic contribution of an individual (or genotype) to the subsequent generation compared to other individuals, determined by differential viability and fertility.

Selective Advantage

The degree to which individuals bearing a specific genotype exhibit higher relative fitness and survival/reproduction in a specific environment compared to alternative genotypes.

Agent of Selection

A specific biotic, abiotic, or anthropogenic external factor in the environment (such as a visual predator, toxic heavy metals in mine tailings, or human artificial breeding) that exerts selective pressure on phenotypes.

Stabilizing Selection

A mode of natural selection on quantitative phenotypes where individuals with intermediate trait values have highest fitness, reducing phenotypic variance without shifting the mean (for example, optimal human birth weight minimizing infant mortality).

Directional Selection

A mode of natural selection where phenotypes at one extreme of the distribution possess higher fitness than average and opposite extreme phenotypes, causing the population trait mean to shift toward the favored extreme over time (such as beak size enlargement in Galápagos finches during drought).

Disruptive Selection

A mode of natural selection where both extreme phenotypic values are favored over intermediate values, increasing bimodal trait divergence within the population and potentially facilitating speciation when coupled with assortative mating.

Industrial Melanism

The evolutionary increase in dark-colored (melanic) morphs in response to industrial soot pollution, exemplified by the peppered moth (Biston betularia), where a single dominant allele of the Cortex gene provided visual camouflage against predatory birds on soot-darkened tree trunks.

Selective Sweep

The rapid increase in frequency and fixation of a beneficial mutation under strong positive selection, which simultaneously drags along closely linked neutral alleles ('genetic hitchhiking') and reduces local nucleotide diversity around the locus (as documented at the SWS2 visual opsin gene in blackwater stickleback fish).

Long-Term Experimental Evolution (LTEE)

A long-running microbial evolution experiment initiated by Richard Lenski tracking 12 replicate populations of Escherichia coli in glucose-limited minimal medium across more than 38 years and $80{,}000$ generations, documenting parallel fitness increases, cell size enlargements, and the novel evolution of citrate utilization ($\text{cit}^+$) after $33{,}000$ generations.

Homozygosity