heteroplasmyA condition in which two genetically different organelles are present in the same cell. The equivalent to heterozygous in the context of nuclear genes.
heteroploidCells with nuclei containing chromosome numbers other than diploid.
heteropyknosisThe property of certain chromosomes, or of their parts, to remain more dense during the cell cycle and to stain more intensely than other chromosomes or…
heterotrophOrganism non capable of self-nourishment utilizing carbon dioxide or carbonates as the sole source of carbon and obtaining energy from radiant energy or…
High Energy EventIn solar-terrestrial terms, flares (class two or more) with outstanding Centimetric Bursts and SID.
High Frequency (HF)The portion of the radio frequency spectrum between between 3 and 30 MHz
High hazardA downstream hazard classification for dams in which more than 6 lives would be in jeopardy and excessive economic loss (urban area including extensive…
High LatitudesWith specific reference to zones of geomagnetic activity, "high latitudes" refers to 50º to 80º geomagnetic.
High liquefaction potentialRefers to the susceptibility of soils to liquefy when subjected to sudden loading, such as intense ground shaking from an earthquake.
High Risk (of severe thunderstorms)Severe weather is expected to affect more than 10 percent of the area. A high risk is rare, and implies an unusually dangerous situation and usually the…
High Seas Forecast(HSF) - Marine forecasts for the major oceans of the world. In this context, major gulfs or seas (e.g.
High SurfLarge waves breaking on or near the shore resulting from swells spawned by a distant storm.
High Surf AdvisoryA High Surf Advisory is issued when breaking wave action poses a threat to life and property within the surf zone. High surf criteria vary by region.
High Surf WarningA High Surf Warning is issued when breaking wave action results in an especially heightened threat to life and property within the surf zone.
high throughput screeningAutomated systems designed to process large numbers of assays, especially in the context of genotyping.
High WindSustained wind speeds of 40 mph or greater lasting for 1 hour or longer, or winds of 58 mph or greater for any duration.
High Wind AdvisoryThis product is issued by the National Weather Service when high wind speeds may pose a hazard. The criteria for this advisory varies from state to state.
High Wind WarningThis product is issued by the National Weather Service when high wind speeds may pose a hazard or is life threatening.
High Wind WatchThis product is issued by the National Weather Service when there is the potential of high wind speeds developing that may pose a hazard or is life…
Higher heating valueQuantity of heat liberated by the complete combustion of a unit volume or weight of a fuel assuming that the produced water vapor is completely condensed…
Higher Heating Value (HHV)(HHV)The maximum heating value of a fuel sample, which includes the calorific value of the fuel (bone dry) and the latent heat of vaporization of the water in…
Higher LubricityThe ability to reduce friction—usually in fuel pumps and fuel injectors.
Highly conserved sequenceA DNA sequence that is very similar in several different kinds of organisms. Scientists regard these cross species similarities as evidence that a…
Highly discordant land useRefers to development that is at variance with the existing condition of the land. It might also be described as incongruous.
Hinge CrackCrack caused by significant changes in water level.
HistocompatibleA tissue or organ from a donor (the person giving the organ or tissue) that will not be rejected by the recipient (the patient in whom the tissue or organ…
histoglobulinThe peptides present on the surface of nucleate cells, responsible for the differences between genetically non-identical individuals that cause rejection…
histology(his-TAH-loh-jee) The study of tissues and cells under a microscope.
histoneA type of protein found in chromosomes. Histones bind to DNA, help give chromosomes their shape, and help control the activity of genes.
HistoricThe time period after the appearance of written records. In the New World, this generally refers to the time period after the beginning of European…
Historic AreaAn area or building in which historic events occurred, or one which has special value due to architectural or cultural features relating to the heritage…
Historic propertiesAny prehistoric or historic districts, sites, buildings, structures, or objects included in, or eligible for inclusion in, the National Register of…
Historic resourcesMaterial remains and the landscape alterations that have occurred since the arrival of Euro-Americans.
HistosolWet organic soils, such as peats and mucks.
HLAOne of a group of proteins found on the surface of white blood cells and other cells that play an important part in the body's immune response to foreign…
HMD(Hemispheric Map Discussion)- This discussion is issued once a day around 1 PM EST (2 PM EDT) and is primarily intended to provide insight into the…
Hoar FrostA deposit of interlocking crystals formed by direct sublimation on objects, usually those of small diameter freely exposed to the air, such as tree…
HoarfrostHoarfrost A deposit of interlocking ice crystals (hoar crystals) formed by direct sublimation on objects, usually those of small diameter freely exposed…
HodographA polar coordinate graph which shows the vertical wind profile of the lowest 7000 meters of the atmosphere.
HOEA shovel that digs by pulling a broom-and-stick-mounted bucket toward itself.
Hoechst dyeA dye used to identify hematopoietic stem cells (HSCs).
Hog fuel or hogged fuelWood residues processed through a chipper or mill to produce coarse chips normally used for fuel.
HogbackRidge formed by erosion of resistant, steeply inclined sedimentary layers.
HogbacksAn eroded steep ridge of resistant rocks produced by erosion of the broken edges of highly tilted strata.
HoistThe mechanism by which a bucket or blade is lifted, or the process of lifting it.
HoleThe vacancy where an electron would normally exist in a solid; behaves like a positively charged particle.
hollow fibreA tube of porous material, with an internal diameter of a fraction of a millimetre, making its ratio of surface area to internal volume very large.
Hollow-jet valveA valve having a closing member that moves upstream to shut off the flow. The hollow-jet valve discharges a hollow or annular jet dispersed over a wide…
holocelluloseThe total carbohydrate fraction of wood; cellulose plus hemicellulose.
HoloceneThe past 10,000 years of geologic time. The most recent epoch of the Quaternary period.
Holocene epochan epoch of the Quaternary period dating from the end of the Pleistocene approximately 11,500 years ago until the present.
holometabolousAn insect that undergoes complete metamorphosis to the adult from a morphologically distinct larval stage.
holoprosencephalyA birth defect where the forebrain does not separate properly into two halves during early fetal life.
Home Energy Rating Systems (HERS)(HERS)A nationally recognized energy rating program that gives builders, mortgage lenders, secondary lending markets, homeowners, sellers, and buyers a precise…
HomeoboxA highly conserved 180 bp DNA sequence that controls body part-, organ- or tissue-specific gene expression, most particularly involved in segmentation in…
homeotic genesGenes that act in concert to determine fundamental patterns of development.
homeotic mutationA mutation that causes a body part to develop in an inappropriate position in an organism, such as the mutation in Drosophila melanogaster that causes…
homoalleleOne of a number of otherwise identical alleles which differ at the same site in their sequence.
homodimerA protein comprising two identical polypeptide chains, or a dimer of identical residues.
homoduplex DNAA double-stranded fully complementary DNA molecule.
homoeologousReferring to chromosome s which are descended from a common progenitor, but which have evolved to be no longer fully homologous.
homogameticProducing similar gametes with regard to the sex chromosomes . In mammals, the female is homogametic (XX), and the male is heterogametic (XY).
HomogeneousLooking the same at every location. Homogeneous milk has no lumps or impurities; it remains the same no matter where you look.
Homogeneous earthfill damAn embankment dam construction throughout of more or less uniform earth materials, except for possible inclusion of internal drains or blanket drains.
Homogeneous Rolled Earth DamAn embankment dam constructed of similar earth material throughout, except for possible inclusion of internal drains or drainage blankets; distinguished…
homogenotizationAn allele replacement technique, in which a bacterial cell is transformed with a plasmid containing an altered copy of the target sequence, and a double…