Biology

Gammaproteobacteria A major class of gram-negative Proteobacteria including diverse free-living and pathogenic genera such as Pseudomonas, Escherichia, Vibrio and Francisella, important in ecology, me…

Ganglion (nervous system): structure, types, and functions Ganglion A ganglion is a cluster of neuronal cell bodies. This article explains its structure, major types in vertebrates and invertebrates, development, and clinical and comparative signif…

Gas exchange in organisms Gas exchange Gas exchange is the movement of oxygen and carbon dioxide between organisms and their environment. It occurs by diffusion across specialized surfaces in animals, plants, fungi and…

Gastralia (belly ribs): ventral dermal bones in reptiles Gastralia Gastralia, or belly ribs, are dermal bones in the ventral body wall of some reptiles and fossil taxa. They support the abdomen, may assist breathing, and inform reconstructions of…

Gastrulation: formation of germ layers and establishment of the body plan Gastrulation Gastrulation is an early embryonic phase when the blastula reorganizes into the gastrula, producing the primary germ layers (ectoderm, mesoderm, endoderm) and establishing axes and…

Gel electrophoresis: principles, types, and applications Gel electrophoresis Gel electrophoresis separates macromolecules such as DNA and proteins by size and charge using a porous gel and an electric field. Common formats include agarose and polyacrylamide…

Gene: units of heredity — structure, function, and significance Gene A gene is a segment of DNA that carries instructions for traits or cellular functions. This article explains gene structure, expression, inheritance, history, and applications in m…

Gene duplication: mechanisms, evolutionary significance, and impacts Gene duplication Gene duplication is the copying of DNA segments that contain genes. It supplies raw material for new functions, shapes genomes through time, and has medical and agricultural import…

Gene expression: how genetic information produces functional molecules Gene expression Overview of gene expression: processes (transcription, translation), regulation, roles in development and disease, common mechanisms, and experimental approaches.

Gene family: definition, origins, structure, and biological roles Gene family A gene family is a group of related genes that arose by duplication and divergence. This article explains how families form, their typical organization, examples, evolutionary sign…

Gene flow: movement of genes and alleles between populations Gene flow Gene flow is the transfer of genetic material (alleles) between populations by movement of organisms, gametes, seeds or human activities; it shapes genetic diversity, adaptation, a…

Gene knockout: methods, applications, and distinctions Gene knockout An overview of gene knockout — deliberate inactivation of genes — covering methods (including CRISPR), types (constitutive, conditional), uses in research and medicine, and key dis…

Gene pool — definition, dynamics, and biological significance Gene pool A gene pool is the complete set of genetic variants present in a local breeding group. This article explains its components, evolutionary forces, measurement, and importance in con…

Gene silencing: mechanisms, biological roles, and applications Gene silencing An overview of gene silencing: molecular mechanisms that reduce or block gene expression, their roles in development and genome defense, and experimental or therapeutic uses.

Gene targeting: methods, applications, and types Gene targeting Gene targeting is the directed replacement or modification of DNA in a genome to study function, create models, or introduce traits. Methods include homologous recombination, engin…

Genetic code: how nucleotide sequences specify proteins Genetic code The genetic code is the set of rules by which nucleotide triplets (codons) in DNA or mRNA specify amino acids during protein synthesis. It is largely universal, degenerate, and cen…

Genetic drift: random changes in allele frequencies Genetic drift Genetic drift is the random fluctuation of allele frequencies in populations, reducing genetic variation over time—especially in small or isolated populations—and distinct from nat…

Genetic engineering: principles, history, techniques, applications and controversies Genetic engineering Overview of genetic engineering: what it is, how it is done, key milestones, common uses, risks and ethical, ecological and legal considerations.

Genetically Modified Organism (GMO) Genetically modified organism Overview of genetically modified organisms: definition, methods, history, applications in agriculture and medicine, regulatory and safety considerations.

Genetics: the science of heredity and biological variation Genetics Overview of genetics: fundamental concepts (genes, DNA, chromosomes), historical milestones, experimental methods, applications in medicine and agriculture, and key distinctions.

Genome: definition, structure, history, and applications Genome A genome is the complete hereditary information of an organism, usually encoded in DNA (or RNA in some viruses). This article covers composition, variation, sequencing, uses, and e…

Genome editing: methods, mechanisms, applications, and ethical considerations Genome editing Genome editing uses engineered nucleases to make precise changes to an organism's DNA. This article explains the methods, molecular repair pathways, applications, history, limitati…

Genomics: study of genomes, methods, history, and applications Genomics Genomics is the scientific study of complete genomes — the full DNA complement of organisms — encompassing sequencing, mapping, function, and large-scale interactions among genes.

Genotype: genetic constitution and its relationship to phenotype Genotype A clear overview of genotype — the inherited genetic constitution of an organism — covering its components, history, ways of study, examples, and how genotype interacts with enviro…

Genus (biological classification) Genus A genus is a principal taxonomic rank grouping closely related species. This article explains its role, naming conventions, history, practical use, and how taxa are delimited and r…

Germ: biological agents, seed embryos, and other meanings Germ Germ — a term with multiple meanings: commonly a disease-causing microbe, the embryonic part of a seed (wheat germ), reproductive germ cells, mathematical germs, and related biolog…

Germ theory of disease Scientific explanation that many infectious diseases are caused by microorganisms; its development transformed medicine, public health, and hygiene practices worldwide.

Gerontology: the multidisciplinary study of aging Gerontology Gerontology is the interdisciplinary study of aging, examining biological, psychological, social, and policy dimensions to understand later life, improve healthspan, inform care, a…

Gestation: biology, variation, and significance in viviparous animals Gestation Gestation is the process by which an embryo or fetus develops inside a viviparous female. This article explains stages, physiological mechanisms, variation among species, and notab…

Giant Gippsland earthworm (Megascolides australis) Giant Gippsland earthworm A very large native Australian earthworm with exceptional length, deep clay burrows and a restricted distribution in South Gippsland; slow growth and habitat loss make it a conserv…

Giant tube worm (Riftia pachyptila) Giant tube worm A large annelid of deep‑sea hydrothermal vents that hosts chemosynthetic bacteria in an internal organ, lacks a digestive tract as an adult, and supports diverse vent communities.

Giardia lamblia (Giardia intestinalis): overview, biology, and public health Giardia lamblia Giardia lamblia is a flagellated protozoan parasite that infects the small intestine of humans and many animals, causing the diarrheal illness giardiasis; transmitted via contamina…

Gill A gill is a respiratory organ that extracts dissolved oxygen from water; found in fish, many amphibians, some invertebrates, and also as a spore-bearing structure in certain fungi.

Gizzard (gastric mill): structure, function, and occurrence in animals Gizzard A gizzard (gastric mill) is a muscular part of the digestive system that mechanically grinds food using ingested grit or internal structures. Found in many birds, some reptiles, cr…

Gland (biology): types, structure, and roles in organisms Gland Overview of glands: definition, major types (endocrine/exocrine), modes of secretion, examples in animals and plants, development, and clinical importance.

Glial cell (neuroglia): types, functions, development and medical importance Glial cell Glial cells are non-neuronal cells in the nervous system that support neurons, provide myelin, regulate the environment, and contribute to immune defense and repair. Overview, type…

Glires: the clade uniting rodents and lagomorphs Glires Glires is the mammalian clade that groups rodents with lagomorphs (rabbits, hares, pikas). It is defined by shared anatomical and genetic traits and has a complex history in morpho…

Globular protein Globular proteins are compact, water-soluble proteins whose folded polypeptide chains perform diverse catalytic, transport, regulatory and storage roles in living systems.

Glow-worm — bioluminescent insects and their biology Glow-worm Glow-worms are bioluminescent insects found worldwide. This article explains their light production, life cycle, main groups, behavior, ecological roles and differences among famil…

Glycogen: animal storage polysaccharide and rapid glucose reserve Glycogen Glycogen is the main multi-branched storage form of glucose in animals, stored as cytosolic granules in liver and muscle and mobilized during fasting or exercise.

Glycolysis: the central glucose breakdown pathway Glycolysis Glycolysis is a conserved ten‑step cytosolic pathway that converts glucose to pyruvate, producing ATP and NADH and serving as the entry point to aerobic and anaerobic energy metabo…

Glycoprotein A glycoprotein is a biomolecule made of a polypeptide linked to carbohydrate chains. They occur on cell surfaces and in secretions, with roles in recognition, signalling, immunity…

Gnathostomata — jawed vertebrates (sharks, bony fish and tetrapods) Gnathostomata Gnathostomata are vertebrates that bear jaws and paired appendages. This clade includes modern jawed fishes and all tetrapods; it arose in the early Paleozoic and diversified in th…

Gnathostomulida (jaw worms): tiny marine interstitial invertebrates Gnathostomulida Gnathostomulida, or jaw worms, are a small phylum of minute marine invertebrates that live between sand grains in shallow coastal sediments and tolerate low-oxygen conditions.

Golden algae (Chrysophyceae): biology, ecology and notable species Golden algae Golden algae (Chrysophyceae) are mostly freshwater protists with golden pigments, siliceous resting cysts and varied nutrition; includes ecologically important planktonic forms and…

Golgi complex (Golgi apparatus): structure, function, and significance Golgi complex Overview of the Golgi complex: its structure, roles in protein and lipid processing, historical discovery, variations across organisms, and importance in cellular transport and hea…

Gonadotropins: LH, FSH and related reproductive hormones Gonadotropin Gonadotropins are pituitary glycoprotein hormones (mainly LH and FSH) that regulate reproductive function in males and females. They act on the gonads and are central to fertility,…

Gonadotropin-releasing hormone (GnRH): role, regulation, and clinical relevance Gonadotropin-releasing hormone Overview of gonadotropin-releasing hormone (GnRH), its secretion from the hypothalamus, role in controlling FSH/LH, pulsatile regulation, developmental activation, and clinical app…