macerateTo disintegrate tissue to disrupt cells. Commonly achieved via mechanical shearing, plasmolysis or enzymatic cell wall degradation.
macromoleculeAny high molecular weight molecule. Often used as a synonym for polymers.
macronutrientA major chemical element essential for normal growth and development. In tissue culture media, macronutrients are those required in concentrations above 0.
macrophageA type of white blood cell that surrounds and kills microorganisms, removes dead cells, and stimulates the action of other immune system cells.
mad cow diseaseColloquial term for bovine spongiform encephalopathy. See proteinaceous infectious particle
MADS boxA highly conserved DNA sequence motif found in a large family of transcription factors, most of which play important roles in developmental processes.
MagentaUsed in four color printing. Reflects blue & red and absorbs green.
major histocompatibility antigenA cell-surface protein or glycoprotein that allows the immune system to distinguish foreign or "non-self" from "self". A better term is histoglobulin.
major histocompatibility complex(Abbreviation: MHC). The large cluster of genes that encode the major histocompatibility antigens in mammals.
Malignant(muh-LIG-nunt) Cancerous. Malignant tumors can invade and destroy nearby tissue and spread to other parts of the body.
malt extractA mixture of organic compounds prepared from malt, used as a culture medium additive.
maltingEnzymatic reduction of starch to sugars in germinating grain, used in brewing.
mammary glandGlandular organ located on the chest. The mammary gland is made up of connective tissue, fat, and tissue that contains the glands that can make milk.
management of farm animal genetic resourcesThe sum total of technical, policy and logistical operations involved in understanding (characterization), using and developing (utilization), maintaining…
mannitol(MA-nih-TOL) A drug used to decrease swelling of the brain and to treat kidney failure.
mannoseA hexose component of many polysaccharides, occasionally used as a carbohydrate source in plant tissue culture media.
MAP1. verb: to determine the relative positions of loci (genes or DNA sequences) on a chromosome.
map distanceThe standard measure of genetic distance between loci, expressed in centiMorgans (cM) or map units .
map unitOne centiMorgan (1 cM) See: map distance; crossing-over unit.
mappingDetermining the physical location of a gene or genetic marker on a chromosome. (See Continuous map, Genetic map, Physical map.)
markerA diagnostic indication that disease may develop.
marker geneA gene of known function or known location, used for marker-assisted selection or genetic studies.
marker peptideA portion of fusion protein that facilitates its identification or purification.
marker-assisted introgressionThe use of DNA markers to increase the speed and efficiency of introgression of a new allele(s) or gene(s) into a breeding population.
marker-assisted selection(Abbreviation: MAS). The use of DNA markers to improve response to selection in a population.
mass selectionAs practised in plant and animal breeding, the selection ofa number of individuals, on the basis of their individual phenotypes, to interbreed to form the…
maternal effectAn effect attributable to a genetic contribution of the female parent of the individual being evaluated.
maternal inheritanceInheritance controlled by non-nuclear genes (e.g. mitochrondria, chloroplast ) that are transmitted only through the female line.
matric potentialA water potential component, always of negative value, resulting from the presence of solid (often finely divided) surfaces; primarily responsible for…
MCSAbbreviation for multiple cloning site. See: polylinker.
MDAAbbreviation for multiple drop array. See: microdroplet array.
MeanA statistics term. The average value in a set of measurements. The mean is the sum of a set of numbers divided by how many numbers are in the set.
MediaAny organization in the business of informing the public with news or commentary.
medianA statistics term. The middle value in a set of measurements.
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 formulationIn tissue culture, the particular constituents for the culture medium, commonly comprising macro- and micro-elements, vitamins, plant hormones, and a…
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 cloningThe cloning of very large DNA fragments. (See Cloning.)
megaDalton(Abbreviation: MDa). One megaDalton is equal to 106 Dalton.
megagametophyteThe female gametophyte; the plant that develops from a megaspore.
megasporeThe female gametophyte in heterosporous plants. Synonym: macrospore.
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.
melting temperature(Abbreviation: Tm). The temperature at which a double-stranded DNA molecule denatures into separate single strands.
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…
memory cellLong-lived B cells and T cells that mediate rapid secondary immune responses to a previously encountered antigen.
Mendel's LawsTwo laws summarizing Gregor Mendel's theory of inheritance. The Law of Segregation states that each hereditary characteristic is controlled by two…
Mendelian populationA natural, interbreeding unit of sexually reproducing plants or animals sharing a common gene pool.
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.
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.
Messenger RNA (mRNA)The class of RNA molecules that copies the genetic information from DNA, in the nucleus, and carries it to ribosomes, in the cytoplasm, where it is…
metabolic cellA cell that is not dividing. See: metabolism
metabolism(meh-TA-boh-lih-zum) The total of all chemical changes that take place in a cell or an organism.
metabolite(meh-TA-boh-lite) A substance made or used when the body breaks down food, drugs or chemicals, or its own tissue (for example, fat or muscle tissue).
metabolomicsThe large-scale study of the full complement of secondary metabolites produced by a given species in all its tissues and growth stages.
metacentric chromosomeA chromosome in which the centromere is located in the middle and, consequently, the chromosome arms are of about equal length.
metal affinity chromatographyA chromatographic technique, in which a compound interacting with a specific metal ion can be captured by immobilizing the relevant ion on the column's…
metalloenzymeAn enzyme which requires the presence of a metal in order to be catalytically active.
MetallothioneinA protective protein that binds heavy metals, such as cadmium and lead.
MetaphaseStage of mitosis or meiosis (following prophase and preceding anaphase ) during which the chromosome s, or at least the kinetochores, lie in the central…
metastasis(meh-TAS-tuh-sis) The spread of cancer from one part of the body to another. A tumor formed by cells that have spread is called a "metastatic tumor" or a…
methylationThe addition of a methyl group (-CH3) to a molecule, most commonly in the context of DNA where cytosine and, less often, adenine residues can be modified…
MHCAbbreviation for major histocompatibility complex.
micro-arrayA large set of cloned DNA molecules immobilized as a compact and orderly pattern of sub-microlitre spots onto a solid matrix (typically a glass slide).
micro-carrierSmall particles used as a support material for (particularly mammalian) cells, which are too fragile to be pumped and stirred as bacterial cells are in a…
micro-elementA nutritional element required in very small quantities.
micro-encapsulationA process of enclosing a substance in very small sealed capsules from which material is released by heat, solution or other means.
micro-environmentA small-scale environment in which the conditions (temperature, humidity, pH etc.
micro-injectionThe introduction of small amounts of (usually) liquid material (DNA, RNA, enzyme s, cytotoxic agents) into a defined tissue or single cell with a fine…
micro-isolating systemMechanical separation of single cells or protoplasts thus allowing them to proliferate individually.
micro-organismOrganism visible only under magnification.
microalgal cultureCulture in bioreactors of microalgae (including seaweeds).