MCSAbbreviation for multiple cloning site. See: polylinker.
MDMesoscale Discussion- When conditions actually begin to shape up for severe weather, SPC (Storm Prediction Center) often issues a Mesoscale Discussion…
MDAAbbreviation for multiple drop array. See: microdroplet array.
Mean Areal Precipitation(abbrev. MAP)- The average rainfall over a given area, generally expressed as an average depth over the area.
Mean Daily TemperatureThe average of the highest and lowest temperatures during a 24-hour period.
Mean DepthThe average depth of water in a stream channel or conduit. It is equal to the cross-sectional area divided by the surface width.
Mean Doppler VelocityReflectivity-weighted average velocity of targets in a given pulse resolution volume. Usually determined from a large number of successive radar pulses.
Mean Low Water(MLW) - A tidal datum. The average of all the low water heights observed over the National Tidal Datum Epoch.
Mean Lower Low Water(MLLW) - A tidal datum. The average of the lower low water height of each tidal day observed over the National Tidal Datum Epoch.
Mean Power Output (of a Wind Turbine)The average power output of a wind energy conversion system at a given mean wind speed based on a Raleigh frequency distribution.
Mean Sea Level(MSL) - The arithmetic mean of hourly water elevations observed over a specific 19-year tidal epoch.
Mean sea level (MSL)The arithmetic mean of hourly water elevations observed over a specific 19-year tidal epoch.
Mean Wind SpeedThe arithmetic wind speed over a specified time period and height above the ground (the majority of U.S.
MeanderBig bend and loops in a river channel as the river snakes through a flat land area.
Meander BeltThe area between lines drawn tangential to the extreme limits of fully developed meanders.
Measured CeilingA ceiling classification applied when the ceiling value has been determined by an instrument, such as a ceilometer or ceiling light, or by the known…
Mechanical SystemsThose elements of building used to control the interior climate.
Mechanismthe means by which an effect or change is produced.
MediaAny organization in the business of informing the public with news or commentary.
medianA statistics term. The middle value in a set of measurements.
Median household incomeDivides households into two equal segments, with one-half of households earning less than the median household income and the other half earning more.
Median housing valueDivides housing units into two equal segments, one-half of housing units less than median housing value and the other half valued more.
Median Wind SpeedThe wind speed with 50 percent probability of occurring.
medium(pl.: media) 1. In plant tissue culture, a term for the liquid or solid formulation upon which plant cells, tissues or organs develop.
Medium Btu GasFuel gas with a heating value of between 200 and 300 Btu per cubic foot.
medium formulationIn tissue culture, the particular constituents for the culture medium, commonly comprising macro- and micro-elements, vitamins, plant hormones, and a…
Medium Frequency(abbrev. MF)- That portion of the radio frequency spectrum from 0.3 to 3 MHz.
Medium PressureFor valves and fittings, implies that they are suitable for working pressures between 125 to 175 pounds per square inch.
Medium RangeIn forecasting, (generally) three to seven days in advance.
Medium-height damA dam between 100 and 300 feet high. See low dam and high dam.
Medium-size water systemA water system that serves greater than 3,300 and less than or equal to 50,000 persons.
Medium-thick arch damAn arch dam with a base thickness to structural height ratio between 0.2 and 0.3 (previously defined as between 0.3 and 0.5).
mega yeast artificial chromosomeA yeast artificial chromosome (YAC) which can carry particularly large inserts (up to 1Mbp) - standard YACs typically carry inserts of up to 500kbp.
megabase(Abbreviation: Mb). A length of DNA consisting of 106 bases.
Megabase (Mb)Unit of length for DNA fragments equal to 1 million nucleotides and roughly equal to 1 cM. See also: centimorgan
Megabase cloningThe cloning of very large DNA fragments. (See Cloning.)
megaDalton(Abbreviation: MDa). One megaDalton is equal to 106 Dalton.
MegafaunaA number of species of presently extinct mammals including mammoths and mastodons.
megagametophyteThe female gametophyte; the plant that develops from a megaspore.
megasporeThe female gametophyte in heterosporous plants. Synonym: macrospore.
MegawattOne thousand kilowatts, or 1 million watts; standard measure of electric power plant generating capacity.
Megawatt (MW)A measure of instantaneous electric power consumption or production. Equal to one thousand KW.
Megawatt electrical (MWe)One million watts of electrical energy; a measure of electrical power capacity, use in PEIS is synonymous with MW.
Megawatt-hourOne thousand kilowatt-hours or 1 million watt-hours.
MeiosisA special form of cell division in which each daughter cell receives half the amount of DNA as the parent cell.
meiotic analysisThe use of patterns of chromosome pairing at meiotic prophase and metaphase to detect relationships between chromosomes, from which can be deduced the…
meiotic driveAny mechanism that causes a particular allele or chromosome to be over-represented in a population of gametes.
melanin(MEH-luh-nin) A pigment that gives color to skin and eyes and helps protect it from damage by ultraviolet light.
Melanocyte(mel-AN-o-site) A cell in the skin and eyes that produces and contains the pigment called melanin.
melanoma(MEH-luh-NOH-muh) A form of cancer that begins in melanocytes (cells that make the pigment melanin).
melting layerThe layer below the 0°C isotherm where snowflakes melt and turn into raindrops.
Melting LevelThe altitude which ice crystals and snowflakes melt as they descend through the atmosphere.
Melting PointThe temperature at which a solid substance undergoes fusion, changing from a solid to a liquid state. Contrast with freezing point.
melting temperature(Abbreviation: Tm). The temperature at which a double-stranded DNA molecule denatures into separate single strands.
Membrane (diaphragm)A membrane or sheet or thin zone or facing, made of a flexible impervious material such as asphaltic concrete, plastic concrete, steel, wood, copper…
membrane bioreactorA vessel in which cells are cultured on or behind a permeable membrane, which allows the diffusion of nutrients to the cells, but retains the cells…
memoryData storage in the form of chips, or the actual chips used to hold data; storage is used to describe memory that exists on tapes or discs.
memory cellLong-lived B cells and T cells that mediate rapid secondary immune responses to a previously encountered antigen.
Memory cellsA subset of antigen-specific T or B cells that "recall" prior exposure to an antigen and respond quickly without the need to be activated again by CD4…
Mendel's LawsTwo laws summarizing Gregor Mendel's theory of inheritance. The Law of Segregation states that each hereditary characteristic is controlled by two…
Mendel, Johann (Gregor)Austrian biologist, born in 1822 and died in 1884, who laid the foundations for the science of genetics.
Mendelian inheritanceManner in which genes and traits are passed from parents to children. Examples of Mendelian inheritance include autosomal dominant, autosomal recessive…
Mendelian populationA natural, interbreeding unit of sexually reproducing plants or animals sharing a common gene pool.
MeniscusThe curved top of a column of liquid in a small tube caused by surface tension.
Merchant generatorA generating plant built with no energy sales contracts in place.
MerchantableLogs from which at least of the volume can be converted into sound grades of lumber ("standard and better" framing lumber).
Mercury BarometerAn instrument for measuring atmospheric pressure. The instrument contains an evacuated and graduated glass tube in which mercury rises or falls as the…
Mercury Vapor LampA high-intensity discharge lamp that uses mercury as the primary light-producing element. Includes clear, phosphor coated, and self-ballasted lamps.
mericlinalRefers to a chimera with tissue of one genotype partly surrounded by that of another genotype.
mericloningA propagation method using shoot tips in culture to proliferate multiple buds, which can then be separated, rooted and planted out.
meridian(meh-RID-ee-un) In traditional Chinese medicine, one of 20 channels that form a network through which qi (the body's vital energy) flows and that connect…
Meridional circulationMeridional circulation An atmospheric circulation in a vertical plane oriented along a meridian.
Meridional FlowLarge-scale atmospheric flow in which the north-south component (i.e., longitudinal, or along a meridian) is pronounced.
meristeleThe branch of a stele supplying the leaf.
meristemUndifferentiated but determined plant tissue, in which the cells are capable of active division and differentiation into specialized tissues such as…
meristem cultureA tissue culture containing meristematic dome tissue without adjacent leaf primordia or stem tissue.
meristem tipAn explant comprising the meristem (meristematic dome) and usually one pair of leaf primordia.
meristem tip cultureCultures derived from meristem tip explants . Used widely to achieve virus elimination and axillary shoot proliferation, less commonly for callus…
meristemoidA localized group of callus cells, characterized by their accumulation of starch, RNA and protein, and giving rise to adventitious shoots or roots.
merozygotePartial zygote produced by a process of partial genetic exchange, such as transformation in bacteria.
MesaA broad, flat-topped elevation with one or more steeply-sloping to vertical sides.
Mesemchymal stem cellAlso known as bone marrow stromal cells, mesenchymal stem cells are rare cells, mainly found in the bone marrow, that can give rise to a large number of…