BIOL 184: Evolution, Biodiversity, and Organismal Biology

Comprehensive vocabulary flashcards covering evolutionary mechanisms, genetics, cladistics, and the phylogenetic diversity of animal and plant lineages from BIOL 184.

Ploidy

The number of complete sets of chromosomes present in the cell or genome of an organism.

Ploidy Formula

The conventional notation used to represent the ploidy level and total chromosome count in an organism's genome, written in the general form $Yn = \text{total number}$.

Haploid (Monoploid)

A cell or organism possessing a single set of unpaired chromosomes ($n$).

Diploid

A cell or organism possessing two complete sets of homologous chromosomes ($2n$), which may carry different alleles.

Homologous Chromosomes

A pair of corresponding chromosomes in a diploid organism that carry the same gene loci but are not identical because each parent contributes one.

Sister Chromatids

Two identical copies of a duplicated chromosome produced during interphase, temporarily held together by a single centromere before separating during cell division.

Binary Fission

The asexual mode of reproduction and cell division in prokaryotes, wherein a single cell duplicates its circular genome and divides into two identical daughter cells.

Mitosis

The process of eukaryotic cell division that duplicates the genome and condenses chromosomes to produce two daughter cells with identical genomes and ploidy levels.

Biological Fitness

The total number of viable offspring (or replicate daughter cells) produced by an individual organism over the course of its entire lifetime.

Evolution (Definition #1)

The change in the average value of a genetically based characteristic in a population over time (descent with modification).

Four Forces of Evolution

The four main evolutionary processes that alter genetic composition across generations: natural selection, mutation, gene flow, and genetic drift.

Phenotype

Any observable or measurable characteristic or suite of traits belonging to an individual organism, determined by both genetic and non-genetic factors.

Genotype

The specific nucleotide sequence or combination of alleles residing in an individual organism's genome.

Ontogenetic Change

The natural phenotypic changes occurring within an individual organism over the course of its developmental history, such as growth and aging.

Phenotypic Plasticity

The capacity of a single genotype to express distinctly different phenotypes when exposed to varying environmental conditions.

Natural Selection

The evolutionary process in which individual phenotypic differences cause differential survival and reproduction (fitness) within a generation, resulting in adaptive evolution.

Selection Differential

A quantitative metric expressing the direction and magnitude of natural selection acting on a phenotypic trait within a population.

Adaptation

As a noun, a trait that enhances an organism's relative fitness in a specific environment; as a verb, the evolutionary process driven by natural selection leading to a population becoming better suited to local conditions.

Mutation

A rare, random error occurring during DNA replication in mitosis or meiosis that serves as the ultimate source of all novel genetic variation.

Point Mutation

A small-scale mutation altering one or a few base pairs in a nucleotide sequence, which includes substitutions, insertions, deletions, and inversions.

Synonymous Mutation

A neutral base substitution that alters a codon without changing the encoded amino acid, resulting in no detectable effect on the phenotype or fitness.

Germ Cells

Specialized reproductive cells (such as spermatogonia and oogonia) capable of undergoing meiosis to produce gametes; mutations in these cells are heritable by offspring.

Somatic Cells

All non-germ cells forming the body of a multicellular organism that divide via mitosis; mutations within somatic cells cannot be passed to offspring.

Gene

A discrete, physical, and functional unit of heredity composed of a specific sequence of nucleic acids.

Locus

The specific physical position or address of a gene along the length of a chromosome.

Allele

One of two or more alternative versions of a gene residing at the same chromosomal locus, differing by nucleotide sequence variation.

Meiosis

A two-stage nuclear division in sexually reproducing eukaryotes that reduces the chromosome number from diploid ($2n$) to haploid ($n$), yielding four genetically non-identical daughter cells.

Crossing Over (Recombination)

The reciprocal exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I of meiosis, creating recombinant chromatids.

Animal Life Cycle

A diploid-dominant sexual cycle containing four main phases: gamete fusion into a diploid zygote ($2n$), diploid somatic growth by mitosis, meiosis in germ cells, and a brief haploid phase ($n$) restricted to gametes.

Taxon

A formal named taxonomic unit or group of organisms at any level of biological classification (plural: taxa).

Phylogenetic Tree (Dendrogram)

A branching diagram depicting an evidence-based hypothesis about the evolutionary relationships and genealogical descent among taxa.

Node

A branch point on a phylogenetic dendrogram representing the most recent common ancestor from which descendant lineages diverged.

Sister Taxa

Two or more taxa or clades that share an immediate most recent common ancestor on a phylogenetic tree not shared by any other group.

Monophyletic Group (Clade)

A taxonomic grouping consisting of a most recent common ancestor and all of its evolutionary descendants, without excluding any taxon.

Paraphyletic Group

An unnatural evolutionary grouping that includes an ancestral taxon and some, but not all, of its descendant taxa.

Polyphyletic Group

An artificial taxonomic group consisting of taxa derived from distinct evolutionary lineages that excludes their most recent common ancestor.

Shared Ancestral Character

A homologous character that originated in an ancestor older than the common ancestor of the clade and is retained in members of the group.

Shared Derived Character (Synapomorphy)

An evolutionary innovation unique to a particular clade that was absent in its immediate ancestral group.

Principle of Parsimony

The scientific rule stating that the preferred phylogenetic tree hypothesis is the one that requires the fewest evolutionary transitions or character changes.

Molecular Clock

An evolutionary yardstick using constant rates of neutral mutation accumulation in specific genomic regions to gauge the absolute time elapsed since divergence.

Homoplasy (Convergent Evolution)

The independent evolutionary appearance of similar character states or adaptations in distantly related taxa due to similar selective pressures rather than shared ancestry.

Metazoa

The monophyletic clade comprising all animals: multicellular, heterotrophic, diploid-dominant eukaryotes with cells supported externally by collagen rather than cell walls.

Choanocytes

Flagellated collar cells unique to sponges (Porifera) that pump water through the interior body and trap suspended food particles in a mucus-coated collar.

Eumetazoa

The sub-clade of animals that possess differentiated, organized true embryonic tissues, excluding Porifera.

Radial Symmetry

A body plan arranged around a central axis such that any imaginary longitudinal cut through that axis yields mirror-image halves; lacks distinct head or front/rear ends.

Bilateral Symmetry

A body plan possessing a single sagittal plane dividing the organism into left and right mirror halves, with distinct dorsal/ventral and anterior/posterior orientations.

Cephalization

The evolutionary specialization and concentration of sensory structures, nervous tissue, and the mouth at the anterior end of a bilaterally symmetric animal.

Diploblastic

An embryonic tissue organization derived from two primary germ layers: an outer ectoderm and an inner endoderm, typical of cnidarians.

Triploblastic

An embryonic tissue organization derived from three primary germ layers: ectoderm, mesoderm, and endoderm, characteristic of all bilaterians.

Cnidocytes

Specialized predatory and defensive stinging cells exclusive to cnidarians that discharge coiled, stinging or adhesive capsules called nematocysts.

Polyp and Medusa

The two primary morphological forms in Cnidaria: polyps are sessile cylindrical forms adhering to substrate with upward-facing mouths, whereas medusae are free-floating, bell-shaped, mobile forms with downward-facing mouths.

Protostome Development

A developmental pattern characterized by spiral and determinate cleavage, schizocoelous coelom formation (splitting of solid mesoderm), and the blastopore becoming the mouth.

Coelom

A fluid- or air-filled body cavity positioned between the outer body wall and digestive tract that is completely lined by mesoderm-derived tissue.

Lophotrochozoa

A major clade of protostome bilaterians whose members exhibit either a lophophore feeding organ, a trochophore larval stage, or share defining molecular synapomorphies (e.g., flatworms, annelids, and molluscs).

Platyhelminthes

The flatworms: a triploblastic, unsegmented, acoelomate protostome phylum lacking a circulatory system, possessing an incomplete gastrovascular cavity, and exhibiting bilateral symmetry.

Annelida

The segmented worms: a coelomate, triploblastic protostome phylum characterized by true body segmentation (metamerism) and a closed circulatory system.

Parapodia

Paired, fleshy lateral appendages found on the body segments of errantian annelids (bristleworms), used for locomotion and respiration.

Mollusca

An unsegmented, coelomate protostome phylum with a body plan typically comprising three main parts: a muscular foot, a visceral mass, and a mantle; usually possesses an open circulatory system.

Open Circulatory System

A circulatory system in which hemolymph is pumped into open sinuses surrounding organs rather than being permanently confined within vessels.

Closed Circulatory System

A circulatory system in which blood moves entirely within a continuous circuit of vessels, distinct from the interstitial fluid (found in annelids, cephalopods, and vertebrates).

Cephalopoda

A class of active, predatory molluscs characterized by a closed circulatory system, advanced sensory eyes, complex brains, and shells that are typically reduced, internalized, or absent.

Ecdysis

The periodic shedding or molting of an external non-cellular cuticle or exoskeleton, which characterizes the ecdysozoan invertebrates.

Nematoda

The roundworms: an unsegmented ecdysozoan phylum covered by a tough cuticle that lacks a true coelom and possesses no circulatory system.

Arthropoda

A hyper-diverse ecdysozoan phylum characterized by segmented bodies, jointed appendages, a chitinous exoskeleton, a reduced coelom, and an open circulatory system.

Trilobita

An extinct group of early marine arthropods characterized by a three-lobed, segmented exoskeleton; flourished in the Cambrian and left no living descendants.

Hexapoda

The subphylum of arthropods comprising insects, distinguished by a body divided into head, thorax, and abdomen, six walking legs, and widespread terrestrial adaptation.

Complete Metamorphosis

A developmental pathway in insects comprising distinct larval forms (e.g., caterpillars, grubs), an intermediate pupal stage, and an adult form morphologically distinct from the larva.

Parasitoid

An insect whose larvae live as parasites inside or on a host organism, ultimately consuming and killing the host before completing development.

Deuterostome Development

A developmental pattern characterized by radial and indeterminate cleavage, enterocoelous coelom formation from archenteron pouches, and the blastopore becoming the anus.

Echinodermata

A marine deuterostome phylum characterized by an endoskeleton of calcareous plates, adults with pentameral symmetry, bilaterally symmetric larvae, and an open water vascular system.

Water Vascular System

A hydraulic network of fluid-filled canals unique to echinoderms that branches into contractile tube feet, functioning in locomotion, feeding, and gas exchange.

Chordata

A bilaterian deuterostome phylum defined by four shared derived morphological characters: a notochord, a dorsal hollow nerve cord, pharyngeal slits or clefts, and a muscular post-anal tail.

Notochord

A flexible, longitudinal rod composed of fluid-filled cells situated between the digestive tract and dorsal nerve cord, providing skeletal support in chordates.

Cyclostomes

The clade of living jawless vertebrates comprising hagfishes (Myxini) and lampreys (Petromyzontida) with cartilaginous skulls and rudimentary vertebral columns.

Chondrichthyes

The cartilaginous fishes (sharks, rays, and chimaeras), possessing jaws derived from skeletal gill arches, mineralized teeth, and an endoskeleton formed of cartilage.

Dermal Denticles

Tooth-like placoid scales that form the skin covering of cartilaginous fishes (Chondrichthyes), reducing drag and providing physical defense.

Osteichthyans

The clade of bony fishes and tetrapods possessing an ossified, mineralized endoskeleton and lungs or lung derivatives (such as swim bladders).

Tetrapods

The clade of osteichthyans characterized by four limbs bearing skeletal digits, adapted for colonization and locomotion on terrestrial land.

Amniotic Egg

A specialized, shelled egg containing four extraembryonic membranes (amnion, chorion, yolk sac, allantois) that allowed terrestrial vertebrates to reproduce independently of water.

Mammalia

The amniote clade distinguished by the presence of hair/fur and mammary glands producing milk for nourishing young.

Embryophyta

The monophyletic clade of land plants within Archaeplastida characterized by alternating generations and multicellular, dependent embryos nurtured by maternal tissues.

Alternation of Generations

A plant reproductive life cycle wherein a multicellular haploid gametophyte generation alternates with a multicellular diploid sporophyte generation.

Gametophyte

The multicellular haploid ($n$) phase of the plant life cycle that produces gametes (sperm and egg) by mitosis.

Sporophyte

The multicellular diploid ($2n$) phase of the plant life cycle that produces haploid spores via meiosis within sporangia.

Sporangium

A multicellular capsule or organ on the plant sporophyte where diploid cells undergo meiosis to generate walled, haploid spores (plural: sporangia).

Sporopollenin

A highly resilient, durable biopolymer coating the walls of plant spores and pollen grains, preventing desiccation and decay in harsh environments.

Apical Meristem

A region of active cell division (mitosis) localized at the growing tips of plant roots and shoots that drives elongation and tissue differentiation.

Gametangium

A specialized multicellular organ of the plant gametophyte responsible for producing gametes (plural: gametangia).

Archegonium and Antheridium

The female and male gametangia of plants, respectively; an archegonium produces a single non-motile egg, whereas an antheridium produces and releases sperm.

Bryophytes

The nonvascular land plants (mosses, liverworts, hornworts), characterized by a gametophyte-dominant life cycle, absence of vascular tissue, rhizoids instead of true roots, and dependence on water for fertilization.

Rhizoids

Root-like cellular filaments that anchor bryophyte gametophytes to the substrate without functioning in primary water or nutrient uptake.

Sphagnum (Peat Moss)

A genus of wetland moss forming extensive, slowly decomposing peat deposits that act as an enormous global terrestrial reservoir of organic carbon.

Xylem

Vascular tissue in plants that conducts water and dissolved minerals upward from roots, strengthened by lignin to provide rigid mechanical support.

Phloem

Vascular tissue composed of living cells that transports sugars, amino acids, and other photosynthetic products throughout the plant body.

Lignin

A rigid polymer reinforcing the cell walls of xylem elements, providing the compressive strength needed for vascular plants to grow tall on land.

Prothallus

The small, free-living, heart-shaped multicellular haploid gametophyte of a homosporous fern, bearing antheridia and archegonia for fertilization.

Homospory

The production of a single size and type of spore that develops into a bisexual gametophyte producing both eggs and sperm (typical of bryophytes and most ferns).

Heterospory

The production of two distinct sizes of spores: megaspores that give rise to female gametophytes and microspores that give rise to male gametophytes (typical of all seed plants).

Seed

A reproductive adaptation of seed plants consisting of a multicellular plant embryo and a nutritive food supply enclosed within a protective maternal seed coat.

Pollen Grain

A microscopic, sporopollenin-coated male gametophyte produced from a microspore, capable of wind- or animal-mediated dispersal without requiring water for fertilization.