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Homo heidelbergensis
Homo heidelbergensis, an extinct archaic human species named after the 1907 Mauer jaw near Heidelberg, lived about 700,000–200,000 years ago in Africa and Europe; debated ancestor of Neanderthals, Denisovans, and modern humans.
Homo juluensis
Homo juluensis (巨颅, "large head people"), a proposed archaic human species named by Bae and Wu in 2024 from Xujiayao (holotype) and Xuchang (paratype) fossils in China, with a contested hypodigm including Denisovans.
Homo luzonensis
Homo luzonensis, or Callao Man, is an extinct small-bodied human species from Callao Cave, Luzon, Philippines, named in 2019; 13 fossils show australopithecine-like hands and feet, modern-like teeth, and dates revised to about 134,000 years.
Homo naledi
Homo naledi ("star" in Sesotho) is an extinct small-brained Homo species from the Rising Star cave system, South Africa, discovered 2013, over 1,550 fossils, dated 335,000-236,000 years ago; deliberate burial claims remain contested.
Homocitrate synthase
Homocitrate synthase (EC 2.3.3.14, HCS; yeast Lys20/Lys21) catalyzes 2-oxoglutarate plus acetyl-CoA to homocitrate, the first committed step of fungal lysine biosynthesis, feedback inhibited by lysine and an antifungal and metabolic-engineering target.
Homocysteine
Homocysteine, a sulfur amino acid from methionine metabolism (hyperhomocysteinemia >15 µmol/L), is lowered by B vitamins, but trials show no reduction in heart attack or death; used mainly for B-vitamin deficiency and homocystinuria testing.
Homocystinuria
Homocystinuria (HCU), also called classic homocystinuria when caused by CBS deficiency, is a rare autosomal recessive metabolic disorder of homocysteine breakdown, causing lens dislocation, skeletal changes, and thromboembolism, treated with vitamin B6, low-methionine diet, and betaine.
Homocystinuria due to cystathionine beta-synthase deficiency
Homocystinuria due to cystathionine beta-synthase deficiency is an inherited disorder of sulfur amino acid metabolism in which homocysteine accumulates, causing thrombosis, lens dislocation, and skeletal changes.
Homocystinuria without methylmalonic aciduria
Homocystinuria without methylmalonic aciduria (functional methionine synthase deficiency; cblE, cblG, cblDv1) is a rare autosomal recessive cobalamin metabolism disorder with megaloblastic anemia, high homocysteine, low methionine, and normal methylmalonic acid, treated with hydroxocobalamin.
Homogeneous assay
A homogeneous assay is a biochemical assay format that measures molecular binding or enzymatic activity with no separation or wash step, so mix-and-read protocols suit automation and high-throughput screening.
Homogentisate 1,2-dioxygenase
Homogentisate 1,2-dioxygenase (HGD, HGO, EC 1.13.11.5) is an Fe(II)-dependent cupin enzyme converting homogentisate to maleylacetoacetate in tyrosine catabolism; its gene sits at 3q13.33 and its deficiency causes alkaptonuria.
Homologous chromosome
Homologous chromosome: one of a matching pair of chromosomes, one maternal and one paternal, that pair and recombine during meiosis; basis of the Sutton-Boveri chromosome theory and genetic mapping.
Homologous recombination
Homologous recombination, also called recombination repair, is a DNA repair pathway that uses a homologous template, usually a sister chromatid, to accurately repair double-strand breaks.
Homology (biology)
Homology (biology): similarity of a gene, structure, or behavior in two organisms because a common ancestor possessed it; contrasted with homoplasy and analogy, tested by character congruence.
Homology Directed Repair
Homology directed repair (HDR) is a DNA double-strand break repair family, spanning error-free homologous recombination, error-prone single strand annealing, and MMEJ, that uses homologous templates and underlies precise CRISPR gene editing.
Homology modeling
Homology modeling, also called comparative modeling, is a computational method that predicts a protein's 3D structure using homologous proteins with known structures as templates, with accuracy depending on sequence identity.
Homomya
Homomya (Agassiz) is a fossil marine bivalve genus in the family Pholadomyidae, order Pholadomyida, ranging from Early Triassic to middle Eocene, with infaunal suspension-feeding species in Jurassic and Cretaceous strata of Europe, Asia, and Texas.
Homonymous hemianopsia
Homonymous hemianopsia (homonymous hemianopia): loss of the same half of the visual field in both eyes from retrochiasmal lesions (optic tract, LGN, radiations, occipital cortex), usually stroke; macular sparing localizes to occipital cortex.
Homoserine dehydrogenase
Homoserine dehydrogenase (EC 1.1.1.3, hom gene) reduces aspartate semialdehyde to homoserine, the committed step toward threonine, methionine, and isoleucine; regulated by threonine feedback, engineered for amino acid production.
Homoserine kinase
Homoserine kinase (HSK, EC 2.7.1.39, thrB) phosphorylates L-homoserine to O-phospho-L-homoserine in threonine biosynthesis; a GHMP kinase whose 2000 Methanocaldococcus jannaschii structure revealed base-free, transition-state-stabilized catalysis.
Homoserine/serine acetyltransferase MetX-like
MetX-like (IPR008220) homoserine/serine acetyltransferases, EC 2.3.1.31, acylate L-homoserine with acetyl-CoA as the committed step of methionine biosynthesis; non-homologous to MetA, Ser-Asp-His triad, druggable in M. tuberculosis.
Homosexual behavior in animals
Homosexual behavior in animals, also called homosexuality in animals or same-sex sexual behavior, is sexual activity between same-sex animals, documented in over 1,500 species including mammals, birds, and insects.
Homosynaptic plasticity
Homosynaptic plasticity: activity-dependent change (LTP or LTD) at synapses that were themselves active during induction, Hebbian, input-specific, NMDA receptor and calcium dependent, distinct from heterosynaptic plasticity at unstimulated synapses.
Homotherium
Homotherium, the scimitar-toothed cat (H. latidens, H. serum), an extinct Holarctic machairodont felid with short serrated canines and long limbs, a cursorial hunter of juvenile mammoths that survived until the terminal Pleistocene.
Homovanillic acid
Homovanillic acid (HVA), also called 4-hydroxy-3-methoxyphenylacetic acid, is the principal end-stage metabolite of dopamine in humans, excreted in urine and used to diagnose tumors such as neuroblastoma.
Homozygote
Homozygote: an individual with two identical alleles at a gene locus, one from each parent; contrasted with heterozygote. Central to recessive disease expression, Bateson's 1902 terminology, and runs of homozygosity used to measure inbreeding.
Homozygous familial hypercholesterolemia
Homozygous familial hypercholesterolemia (HoFH), also called bi-allelic FH, is a rare autosomal semi-dominant disorder with LDL-C above 10 mmol/L from birth, caused mainly by LDLR variants, and treated with statins, ezetimibe, PCSK9 inhibitors, evinacumab, lomitapide, and apheresis.
Honey
Honey is a sweet substance honeybees make from flower nectar or plant secretions and ripen in honeycomb; it is mostly sugars, and legal standards forbid adding ingredients or removing constituents.
Honey badger
Honey badger (Mellivora capensis, ratel): a large mustelid of sub-Saharan Africa, Arabia, and Asia, sole species of Mellivorinae, with loose tough skin, generalist diet, IUCN Least Concern status, and disputed honeyguide cooperation.
Honey bee
Honey bee (Apis mellifera), western honey bee: a eusocial bee with queen, worker, and drone castes living in ~20,000-member colonies that function as superorganisms, communicate food locations by the waggle dance, and face major losses from Varroa mite-borne viruses.