Biology

Tandem repeat (DNA) Tandem repeat Tandem repeats are consecutive copies of short DNA sequences found throughout genomes. They influence genome structure, evolution, heredity, forensics, and certain human genetic di…

Tapeworm (Cestoda): biology, life cycle, health effects and prevention Tapeworm Tapeworms (class Cestoda) are parasitic flatworms that live in vertebrate intestines. This article covers their anatomy, life cycle, human health effects, diagnosis, treatment and…

Taste (gustation): how we perceive basic tastes and flavor Taste Overview of taste (gustation): detection by taste receptors, the five basic tastes, anatomy and brain processing, interaction with smell, evolutionary role, culinary importance, an…

Taste bud Taste buds are sensory structures on the tongue and other oral surfaces that detect the basic tastes, guide food choices, and contribute to flavor and digestive reflexes.

Taxidermy: practice, history, techniques and uses Taxidermy Taxidermy is the preparation and mounting of animal skins for display, study, or memorial purposes. This article explains methods, history, applications, ethical issues and how tax…

Taxon (taxa): definition, ranks, and role in biological classification Taxon A taxon (plural: taxa) is any named or defined group of organisms used in biological classification. This article explains what taxa are, common ranks, historical development, exam…

Taxonomy: principles and practice of classifying organisms Taxonomy Taxonomy is the scientific discipline of naming, describing and organizing living things into groups based on shared characteristics and evolutionary relationships.

Telomerase: structure, function, discovery, and biomedical relevance Telomerase Telomerase is a ribonucleoprotein enzyme that extends telomeres—repeating DNA at chromosome ends—supporting genome stability, stem cell function, and implicated in ageing and cance…

Telomere: structure, function, history and medical relevance Telomere Telomeres are repetitive DNA sequences at chromosome ends that safeguard genetic information. This article explains their structure, role in aging and cancer, discovery, telomerase…

Temporal bone The temporal bone is a complex skull bone at the sides and base of the cranium that houses ear structures, transmits cranial nerves and blood vessels, and varies in form across mam…

Tentacle (limblike organ found in animals and plants) Tentacle A tentacle is a flexible, elongated organ used by various animals and some plants for sensing, grasping, feeding and locomotion. This article describes forms, structure, examples,…

Tephritidae (tephritid fruit flies) Tephritidae Tephritidae is a large family of colorful 'peacock' fruit flies. Many species are agricultural pests while others help control weeds; taxonomy and control methods are active resear…

Terrestrial locomotion: forms, evolution, and adaptations Terrestrial locomotion Overview of how animals move on land, the major modes and mechanics, evolutionary origins, ecological importance, and notable distinctions in morphology and gaits.

Testicle (testis): structure, function, and clinical overview Testicle The testicle (testis) is the male gonad responsible for sperm and testosterone production, typically two in mammals, housed in the scrotum and subject to specific anatomy, physiolo…

Tetrapods — four-limbed vertebrates and their evolutionary significance Tetrapod Tetrapods are vertebrates descended from four-limbed ancestors. This article explains their defining traits, major groups, fossil origins, evolutionary transitions, and notable ada…

Tetrapodomorph: the lineage bridging lobe-finned fishes and tetrapods Tetrapodomorph Tetrapodomorpha is the clade of lobe-finned vertebrates that includes tetrapods and their closest fossil relatives, showing the anatomical changes from finned fish to four-limbed l…

The Genetical Theory of Natural Selection R. A. Fisher's 1930 book that integrated Mendelian genetics with Darwinian natural selection, advancing population genetics and shaping the modern evolutionary synthesis.

The Red Queen (evolutionary hypothesis and its uses) The Red Queen An overview of the Red Queen concept: its origin in Lewis Carroll, Van Valen’s evolutionary hypothesis, its application to sex and coevolutionary arms races, evidence, limits, and…

The Selfish Gene: Richard Dawkins’s gene-centered account of evolution The Selfish Gene Overview of Richard Dawkins's 1976 book The Selfish Gene: its gene-centered interpretation of evolution, the replicator/vehicle distinction, the coinage 'meme', and its scientific…

Theriodont: mammal-like therapsids and the origins of mammals Theriodont Theriodonts are a major clade of therapsids that include gorgonopsians, therocephalians and cynodonts; their mammal-like anatomy and evolutionary steps led to the first true mammal…

Thermophile Organisms adapted to life at high temperatures. Covers definitions, temperature ranges, cellular adaptations, habitats, evolutionary context, and industrial and scientific uses.

Thermoregulation Thermoregulation is an organism's control of internal temperature through physiological and behavioral mechanisms to maintain homeostasis across environments.

Thiotrichales: an order of sulfur‑associated and diverse bacteria Thiotrichales Thiotrichales is an order of Gammaproteobacteria that includes sulfur‑oxidizing filamentous forms, giant cells such as Thiomargarita, and medically important taxa like Francisella.

Thorax (body region) Thorax The thorax is the mid-body region in many animals. In vertebrates it forms the chest enclosing heart and lungs; in arthropods it is the middle tagma bearing legs and wings.

Thrips (Thysanoptera): tiny fringed-wing insects, pests and pollinators Thrips Overview of thrips (order Thysanoptera): appearance, life cycle, ecology, economic importance as crop pests and virus vectors, and approaches to monitoring and control.

Thrombolite — clotted microbial carbonate structures Thrombolite Thrombolites are clotted, accretionary carbonate structures built by microbial communities (often cyanobacteria). They formed in shallow water, were widespread in early Paleozoic s…

Thrombosis: formation, types, symptoms, diagnosis and treatment Thrombosis Thrombosis is the formation of a blood clot inside a blood vessel that impedes circulation. This article explains causes, common locations, symptoms, diagnosis, treatment and preve…

Thymus — primary lymphoid organ for T cell development Thymus The thymus is a central lymphoid organ in the chest where T lymphocytes mature and learn self-tolerance. It is most active in early life and gradually involutes with age; it has cl…

Tibia (shinbone): anatomy, function, development and clinical significance Tibia The tibia, or shinbone, is the larger weight-bearing bone of the lower leg. This article explains its anatomy, growth, functions, common injuries and how it differs from the fibula…

Tissue (biology): structure, types, functions and study Tissue A tissue is a group of similar cells that perform a specific role within multicellular organisms. Covers animal and plant tissues, organization, examples, histology and medical rel…

Tissue culture (cell culture): methods, history and applications Tissue culture Tissue culture (cell culture) is the laboratory growth of plant or animal cells outside the organism. This article summarizes key methods, equipment, history, uses, and common chal…

Tobacco mosaic virus (TMV) Tobacco mosaic virus Tobacco mosaic virus is a rod-shaped, single-stranded RNA virus that infects tobacco and many other plants, causing characteristic mosaic symptoms and serving as a model in virolog…

Toe: anatomy, function, variation and clinical notes Toe Toes are the terminal digits of the foot that contribute to balance, propulsion and manipulation. This article covers their structure, variation among animals, roles in gait and co…

Toll-like receptor (TLR) Toll-like receptor Toll-like receptors are innate immune pattern-recognition proteins that detect microbial molecules, initiate inflammatory signalling and bridge innate and adaptive immunity.

Tongue: anatomy, functions, sensation and clinical overview Tongue Concise encyclopedia entry on the human tongue: structure, surface features, taste, roles in eating and speech, innervation, blood supply, common conditions and basic clinical and…

Tooth: structure, function, development and evolution Tooth Overview of tooth anatomy, types and functions, development and evolution, common disorders and basic care. Covers vertebrate and human variation and the role of teeth in culture a…

Torpor: energy-saving physiological state in birds and mammals Torpor Torpor is a regulated reduction of metabolic rate and body temperature used by some warm-blooded animals to conserve energy when resources are limited. It ranges from short daily e…

Touch: the somatic sense of contact, temperature and pain Touch Touch is the bodily sense that detects contact, pressure, texture, temperature and pain. It relies on cutaneous and deep receptors, nerve pathways and cortical processing to suppor…

Toxicofera Toxicofera: a proposed clade within Squamata uniting snakes and several lizard groups that share an ancient oral toxin system; its recognition changed thinking about the origin of…

Toxoplasma gondii: biology, transmission, and clinical significance Toxoplasma Overview of the protozoan parasite Toxoplasma gondii: life cycle, hosts, transmission routes, clinical effects, prevention and historical notes on discovery and research.

Trace fossil (ichnofossil) Trace fossil Trace fossils are preserved records of organism activity — footprints, burrows, feeding marks, coprolites and microbial structures — used to interpret behaviour, environments and g…

Trachea (windpipe): structure, function and clinical significance Trachea The trachea, or windpipe, is the sturdy, cartilaginous airway that conducts air from the larynx to the lungs. This article explains its anatomy, histology, development and common c…

Trait (biology): definition, types, inheritance and significance Trait A biological trait is any observable feature or behavior of an organism. This article explains types of traits, their genetic and environmental causes, examples, and their role in…

Transcript (record, academic record, and genetic transcription) Transcript A transcript is a written or printed record of spoken words, an official academic record of courses and grades, or the RNA copy produced from DNA during gene expression.

Transcription (genetics): how cells copy DNA into RNA Transcription (genetics) Transcription is the enzymatic process that produces RNA from a DNA template, initiating gene expression and producing mRNA, rRNA, tRNA and other functional RNAs.

Transcription factor — proteins that control gene expression Transcription factor Proteins that bind specific DNA sequences to regulate gene transcription, recruiting or blocking RNA polymerase and coordinating with chromatin modifiers to control when, where and…

Transcriptome: the complete set of RNA molecules expressed by cells Transcriptome The transcriptome is the full collection of RNA molecules produced in a cell or cell population. It reflects gene expression, includes coding and noncoding RNAs, and is measured by…

Transduction (genetics) Transfer of genetic material between cells by viruses; includes bacteriophage-mediated exchange in bacteria and viral-vector delivery used in research and therapy.