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- M -

M13  A single-stranded DNA bacteriophage used as a vector for DNA sequencing.

M13 strand  The single-stranded DNA molecule that is present in the infective form of bacteriophage M13.

mAB  See monoclonal antibody.

macerate  To disintegrate tissues to obtain a cell dissociation. Cutting, soaking or enzymatic actions are commonly used.

macromolecule  Molecule of large molecular weight, such as proteins, nucleic acids and polysaccharides.

macronutrient (Gr. makros, large + L. nutrire, to nourish) For growth media: an essential element normally required in concentrations >0.5 millimole/l.

macrophages  Large, white blood cells that ingest foreign substances and display on their surfaces antigens produced from the foreign substances, to be recognized by other cells of the immune system.

macropropagation  Production of plant clones from growing parts.

major histocompatibility antigen  A cell-surface macromolecule that allows the immune system to distinguish foreign or "non-self" from "self". A better term is histoglobulin (See histocompatibility antigen). These are the antigens that must be matched between donors and recipients during organ and tissue transplants to prevent rejection.

major histocompatibility complex  The large cluster of genes that encode the major histocompatibility antigens in mammals.

malignant  Having the properties of cancerous growth.

malt extract  A mixture of organic compounds from malt, used as a culture medium adjunct. See organic complex; undefined.

malting  A process of generating starch-degrading enzymes in grain by allowing it to germinate in a humid atmosphere. See brewing.

mammary glands  The milk-producing organs of female mammals, which provide food for the young.

mammary tumours  Tumours of the milk glands.

management of farm animal genetic resources  In AnGR: The sum total of technical, policy and logistical operations involved in understanding (characterization), using and developing (utilization), maintaining (conservation), accessing, and sharing the benefits of animal genetic resources. (Source: FAO, 1999)

mannitol (C6H14O6; f.w. 182.17)  A sugar alcohol widely distributed in plants. Mannitol is commonly used as a nutrient and osmoticum (q.v.) in suspension medium for plant protoplasts.

mannose (C6H12O6; f.w. 180.16)  A hexose component of many polysaccharides and mannitol. Mannose is occasionally used as a carbohydrate source in plant tissue culture media.

map  1. Verb: To determine the relative positions of loci on a DNA molecule. Linkage mapping is done by estimating the recombination fraction between loci, from the genotypes of offspring of particular matings. The further apart two loci are on a chromosome, the greater will be the frequency of recombination between them up to a maximum of 50%, the situation observed when they are sufficiently far apart on a chromosome that recombinant gametes are as frequent as non-recombinant gametes, or when they are on different chromosomes. Physical mapping is usually performed by the use of in situ hybridisation of cloned DNA fragments to metaphase chromosomes.

    2. Noun: A diagram showing the relative positions of, and distances between, loci.

map distance  The standard measure of distance between loci, expressed in centiMorgans (cM). Estimated from recombination fraction via a mapping function (q.v.). For small recombination fractions, map distance equals the percentage of recombination (recombination frequency) betwen two genes. 1% recombination = 1 cM. Sometimes called a map unit.

mapping  Determining the location of a locus (gene or genetic marker) on a chromosome. See continuous map; linkage map; physical map.

mapping function A mathematical expression relating observed recombination fraction (q.v.) to map distance expressed in centiMorgans. Two common mapping functions are those developed by Haldane (1919; J. Genet., 8: 299-309) and Kosambi (1944; Ann. Eugen., 12: 172-175). In both functions, the relationship between recombination fraction and map distance is approximately linear for recombination fractions less than 10%; as recombination fraction increases above 10% (up to its maximum of 50%), map distance is increasingly greater than recombination fraction.

map unit  See map distance; crossing-over unit.

marker  An identifiable DNA sequence that facilitates the study of inheritance of a trait or a gene. Such markers are used in mapping the order of genes along chromosomes and in following the inheritance of particular genes: genes closely linked to the marker will generally be inherited with it. Markers must be readily identifiable in the phenotype, for instance by controlling an easily observable feature (such as eye colour) or by being readily detectable by molecular means, e.g., microsatellite markers (q.v.). See gene tracking.

marker-assisted introgression  The use of DNA markers to increase the speed and efficiency of introgression (q.v.) of a new gene or genes into a population. The markers will be closely linked to the gene(s) in question.

marker-assisted selection (MAS)  The use of DNA markers to increase the response to selection in a population. The markers will be closely linked to one or more quantitative trait loci (q.v.).

marker gene  A gene of known function and known location on the chromosome. cf genetic marker.

marker peptide  A portion of fusion protein that facilitates its identification or purification.

MAS  See marker-assisted selection.

mass selection  As practised in plant and animal breeding, the choosing of individuals for reproduction from the entire population on the basis of individual phenotypes.

maternal effect  An effect attributable to some aspect of performance of the mother of the individual being evaluated.

maternal inheritance  Inheritance controlled by extrachromosomal (cytoplasmic) factors that are transmitted through the egg.

matric potential  A water potential component, always of negative value, resulting from capillary, imbibitional and adsorptive forces. See pressure potential.

maturation  The formation of gametes or spores.

MCS  See polylinker.

MDA  Multiple drop array.   See microdroplet array.

mean  In statistics, the arithmetic average; the sum of all measurements or values in a sample divided by the sample size.

media  See culture medium; medium.

median  In a set of measurements, the central value above and below which there are an equal number of measurements.

medium (pl: media)  1. In plant tissue culture, a term for the liquid or solidified formulation upon which plant cells, tissues or organs develop. See culture medium.

    2. In general terms, it could also means a substrate for plant growth, such as nutrient solution, soil, sand, etc., e.g., potting medium.

medium formulation  In tissue culture, the particular formula for the culture medium. It commonly contains macro-elements and micro-elements (high and low salt), some vitamins (B vitamins, inositol), plant growth regulators (auxin, cytokinin and sometimes gibberellin), a carbohydrate source (usually sucrose or glucose) and often other substances, such as amino acids or complex growth factors. Media may be liquid or solidified with agar; the pH is adjusted (ca. 5-6) and the solution is sterilized (usually by filtration or autoclaving). Some formulations are very specific in the kind of explant or plant species that can be maintained; some are very general.

megabase (abbr: Mb)  A length of DNA consisting of 106 base pairs (if double-stranded) or 106 bases (if single-stranded). 1 Mb = 103 kb = 10bp.

megabase cloning  The cloning of very large DNA fragments. See cloning.

megadalton (MDa)  One megadalton is equal to 106 daltons. See dalton.

megaspore; macrospore  A haploid (n) spore developing into a female gametophyte in heterosporous plants.

meiosis (Gr. meioun, to make smaller)  The special cell division process by which the chromosome number of a reproductive cell becomes reduced to half (n) the diploid (2n) or somatic number. Two consecutive divisions occur. In the first division, homologous chromosomes became paired and may exchange genetic material (via crossing over) before moving away from each other into separate daughter nuclei (reduction division). These new nuclei divide by mitosis to produce four haploid nuclei. Meiosis results in the formation of gametes in animals or of spores in plants. It is an important source of variability through recombination.

meiotic analysis  A technique used to analyse chromosome-pairing relationships.

meiotic drive  Any mechanism that causes alleles to be recovered unequally in the gametes of a heterozygote.

meiotic product(s)  See gametes.

melanin  Pigment, as typically produced by specialised epidermal cells called melanocytes.

melting temperature (abbr: Tm)  The temperature at which a double-stranded DNA or RNA molecule denatures into separate single strands. The Tm is characteristic of each DNA species and gives an indication of its base composition. DNAs rich in G:C base pairs are more resistant to thermal denaturation than A:T rich DNA since three hydrogen bonds are formed between G and C, but only two between A and T.

membrane bioreactors  Bioreactors where cells grow on or behind a permeable membrane, which lets the nutrients for the cell through but retains the cells themselves. A variations on this theme is the hollow-fibre reactor.

memory cells  Long-lived B and T cells that mediate rapid secondary immune responses to a previously encountered antigen.

Mendelian population  A natural, interbreeding unit of sexually reproducing plants or animals sharing a common gene pool.

Mendelism  The theory of heredity that forms the basis of classical genetics, proposed by Gregor Mendel in 1866 and formulated in two laws (see Mendel's Laws).

Mendel's Laws  Two laws summarizing Gregor Mendel's theory of inheritance. The Law of Segregation states that each hereditary characteristic is controlled by two `factors' (now called alleles), which segregate and pass into separate germ cells. The Law of Independent Assortment states that pairs of `factors' segregate independently of each other when germ cells are formed. See independent assortment; linkage.

mericlinal  Refers to a chimera with tissue of one genotype partly surrounded by that of another genotype.

mericloning  A propagation method using shoot tips in culture to proliferate multiple buds, which can then be separated, rooted and planted out.

meristele  The vascular cylinder tissue in the stem. See stele.

meristem   (Gr. meristos, divisible)  Undifferentiated but determined tissue, the cells of which are capable of active cell division and differentiation into specialized and permanent tissue such as shoots and roots.

meristem culture  A tissue culture containing meristematic dome tissue without adjacent leaf primordia or stem tissue. The term may also imply the culture of meristemoidal regions of plants, or meristematic growth in culture.

meristem tip  An explant comprising the meristem (meristematic dome) and usually one pair of leaf primordia. Also refers to explants originating from apical meristem tip or lateral or axillary meristem tip. Do not confuse the meristem tip with the term "shoot tip," which is much larger and usually has more immature leaves and stem tissue.

meristem tip culture  Cultures derived from meristem tip explants. The use of meristem tip culture is for virus elimination or axillary shoot proliferation purposes, but less commonly for callus production.

meristemoid  A localized group of cells in callus tissue, characterized by an accumulation of starch, RNA and protein, and giving rise to adventitious shoots or roots.

merozygote  Partial zygote produced by a process of partial genetic exchange, such as transformation in bacteria.

mesh bioreactor  See filter bioreactor.

mesoderm  The middle germ layer that forms in the early animal embryo and gives rise to parts such as bone and connective tissue.

mesophile  A micro-organism able to grow in the temperature range 20 to 50°C; optimal growth often occurs at about 37°C.

mesophyll (Gr. mesos, middle + phyllon, leaf)  Leaf parenchyma tissue occurring between epidermal layers.

messenger RNA  See mRNA.

metabolic cell  A cell that is not dividing.

metabolism (M.L. from the Gr. metobolos, to change)  In an organism or a single cell, the biochemical process by which nutritive material is built up into living matter, or aids in building living matter, or by which complex substances and food are broken down into simple substances.

metabolite  1. A low-molecular-weight biological compound that is usually synthesized by an enzyme.

    2. A compound that is essential for a metabolic process. A substance synthesized by the organism, or taken in from the environment. Autotrophic organisms take in inorganic metabolites, such as water, CO2, nitrates and some trace elements.

metacentric chromosome  A chromosome with the centromere near the middle and, consequently, two arms of about equal length.

metallothionein  A protective protein that binds heavy metals such as cadmium and lead.

metaphase (Gr. meta, after + phasis, appearance)  Stage of mitosis during which the chromosomes, or at least the kinetochores, lie in the central plane of the spindle. It is the stage following prophase and preceding anaphase.

metastasis  The spread of cancer cells to previously unaffected organs.

methionine  A sulphur-containing amino acid.

methylation  The addition of a methyl group (-CH3) to a macromolecule, such as the addition of a methyl group to specific cytosine and, occasionally, adenine residues in DNA.

Michaelis constant  See Km.

microalgal culture  Culture in bioreactors of microalgae; microalgae include seaweeds.

micro-array, DNA  See DNA micro-array.

microbe  A general term for a micro-organism.

microbial mats  Layered groups or communities of microbial populations.

microbody (Gr. mikros, small + body)  A cellular organelle always bound by a single membrane, frequently spherical, from 20 to 60 nm in diameter, containing a variety of enzymes.

micro-carriers  Small particles used as a support material for cells, and particularly mammalian cells, which are too fragile to be pumped and stirred as bacterial cells are in a large-scale culture.

microdroplet array; multiple drop array (MDA); hanging droplet technique. Introduced by Kao and Konstabel (1970), this technique is used to evaluate large numbers of media modifications, employing small quantities of medium into which are placed small numbers of cells. Droplets of liquid are arranged on the lid of a Petri dish, inverted over the bottom half of the dish containing a solution with a lower osmotic pressure, and the dish is sealed. The cells or protoplasts form a monolayer at the droplet meniscus and can easily be examined.

micro-element  An element required in very small quantities.

micro-encapsulation  A process of enclosing a substance in very small sealed capsules from which material is released by heat, solution or other means.

micro-environment (Gr. mikros, small + O.F. environ, about)  The environment close enough to the surface of a living or non-living object to be influenced by it.

microfibrils (Gr. mikros, small + fibrils, diminutive of fibre)  Microfibrils are exceedingly small fibres visible only at the high magnification of the electron microscope.

microgametophytes  See anther.

micrograft  See shoot-tip graft.

micro-injection  The introduction of small amounts of material (DNA, RNA, enzymes, cytotoxic agents) into a single eukaryotic cell with a fine, microscopic needle, penetrating the cell membrane.

micro-isolating system  Mechanical separation of single cells or protoplasts thus allowing them to proliferate individually.

micron; micrometre (Gr. mikros, small)  A unit of distance: 10-6 m; 0.001 mm. Symbol: mm.

2-micron plasmid  See 2mm plasmid.

micronutrient (Gr. mikros, small + L. nutrire, to nourish)  For growth media: An essential element normally required in concentrations < 0.5 millimole/litre.

micro-organism  Organism visible only under magnification.

microplasts  Vesicles produced by subdivision and fragmentation of protoplasts or thin-walled cells.

micropyle  1. A small opening in the surface of a plant ovule through which the pollen tube passes prior to fertilization.

    2. A small pore in some animal cells or tissues.

microprojectile bombardment  A procedure for modifying cells by shooting DNA-coated metal (tungsten or gold) particles into them. See biolistics.

micropropagation  Miniaturized in vitro multiplication and/or regeneration of plant material under aseptic and controlled environmental conditions on specially prepared media that contain substances necessary for growth; used for three general types of tissue: excised embryos (= embryo culture); shoot-tips (= meristem culture or mericloning); and pieces of tissue that range from bits of stems to roots. Four stages of plant tissue culture have been defined by Murashige:
Stage I. Establishment of an aseptic culture.
Stage II. The multiplication of propagules.
Stage III. Preparation of propagules for successful transfer to soil (rooting and hardening).
Stage IV. Establishment in soil.

microsatellite  A form of VNTR (q.v.). Specifically, a segment of DNA characterized by the occurrence of a variable number of copies (from a few up to 30 or so) of a sequence of around 5 or fewer bases (called a repeat unit, q.v.). A typical microsatellite is the repeat unit AC, which occurs at approximately 100 000 different sites in a typical mammalian genome. At any one site (locus), there are usually several different "alleles," each identifiable according to the number of repeat units. These alleles can be detected by PCR (q.v.), using primers designed from the unique sequence that is located on either side of the microsatellite. When the PCR product is run on an electrophoretic gel, alleles are seen to differ in length in units equal to the size of the repeat unit, e.g., if the primers correspond to the unique sequence immediately on either side of the microsatellite and are each 20 bases long, and an individual is heterozygous for an AC microsatellite with one allele comprising 5 repeats and the other comprising 6 repeats, the heterozygote will exhibit two bands on the gel, one band being 20 + (2 × 5) + 20 = 50 bases long, and the other allele being 20 + (2 × 6) + 20 = 52 bases long. Microsatellites have been the standard DNA marker: they are easily detectable by PCR, and they tend to be evenly located throughout the genome. Thousands have been mapped in many different species.

microspore  The smaller of the two kinds of meiospores produced by heterosporous plants in the course of microsporogenesis; in seed plants, microspores give rise to the pollen grain, the male gametophyte.

microtuber  Cultured tissue capable of growing into tuberous plant.

microtubules  A minute filament in living cells that is composed of the protein tubulin and occurs singly, in pairs, triplets or bundles. Microtubules help cells to maintain their shape; they also occur in cilia, flagella and the centrioles, and form the spindle during nuclear division.

middle lamella (L. lamella, a thin plate or scale). Original thin membrane separating two adjacent protoplasts and remaining as a distinct cementing layer between adjacent cell walls.

mid-parent value  In quantitative genetics, the average of the phenotypes of two mates.

minimum effective cell density  The inoculum density below which the culture fails to give reproducible cell growth. The minimum density is a function of the tissue (species, explant, cell line) and the culture phase of the inoculum suspension. Minimum density decreases inversely to the aggregate size and division rate of the stock culture.

minimum inoculum size  The critical volume of inoculum (q.v.) required to initiate culture growth, due to the diffusive loss of cell materials into the medium. The subsequent culture growth cycle is dependent on the inoculum size, which is determined by the volume of medium and size of the culture vessel.

mini-prep  A small-scale (mini-) preparation of plasmid or phage DNA. Used to analyse DNA in a cloning vector after a cloning experiment.

minisatellite  A form of VNTR (q.v.) in which the repeat units (q.v.) typically range from 10 to 100 bases. They are usually detected by Southern hybridization (q.v.), using a probe comprising a clone of the repeat unit. The first DNA fingerprints (q.v.) were minisatellites detected in this way. Minisatellites tend to be located at the ends of chromosomes and in regions with a high frequency of recombination.

minitubers  Small tubers (5-15 mm in diameter) formed on shoot cultures or cuttings of tuber-forming crops, such as potato.

mismatch  The lack of a complementary pair of bases in a double helix of DNA, e.g., A:C, G:T.

mismatch repair  DNA repair processes that correct mismatched base pairs.

missense mutation  A mutation that changes a codon for one amino acid into a codon specifying another amino acid.

mist propagation  Application of fine droplets of water to leafy cuttings in the rooting stage to reduce transpiration. cf fog.

mites  Free-living and parasitic animals belonging to the order Acarina, class Arachnida (with spiders). Mites may infest plant crops, reducing their harvest. They may also infest plant tissue culture work areas and incubation facilities in search of sugars, and so contaminate culture vessels and spread bacteria and fungi.

mitochondrial DNA (mtDNA)  A circular ring of DNA found in mitochondria. In mammals, mtDNA makes up less than 1% of the total cellular DNA, but in plants the amount is variable. It codes for ribosomal RNA and transfer RNA, but only some mitochondrial proteins (up to 30 proteins in animals), the nuclear DNA being required for encoding most of these.

mitochondrion  (Gr. mitos, thread + chondrion, a grain; pl: mitochondria)  A small cytoplasmic organelle that carries out aerobic respiration. Oxidative phosphorylation takes place to produce ATP.

mitosis (Gr. mitos, a thread; adj: mitotic; pl: mitoses)  Disjunction of replicated chromosomes and division of the cytoplasm to produce two genetically identical daughter cells. The division involves the appearance of chromosomes, their longitudinal duplication, and equal distribution of newly formed parts to daughter nuclei. It is separated into five stages: interphase, prophase, metaphase, anaphase and telophase.

mixed bud  A bud containing both rudimentary leaves and flowers.

mixoploid  Cells with variable (euploid, aneuploid) chromosome numbers. Mosaics or chimeras differ in chromosome number as a result of a variety of mitotic irregularities.

mobilization  1. The transfer between bacteria of a non-conjugative plasmid by a conjugative plasmid.

    2. The transfer between bacteria of chromosomal genes by a conjugative plasmid.

mobilizing functions  The genes on a plasmid that give it the ability to facilitate the transfer of either a non-conjugative or a conjugative plasmid from one bacterium to another.

modal class; mode  In a frequency distribution, the class having the greatest frequency.

model  A mathematical description of a biological phenomenon.

modification  1. Enzymatic methylation of a restriction enzyme DNA recognition site.

    2. Specific nucleotide changes in DNA or RNA molecules.

modifier; modifying gene  A gene that affects the expression of some other gene.

MOET  See multiple ovulation and embryo transfer.

molality  The number of moles of solute per litre of solvent.

molarity  The number of moles of a substance contained in a kilogram of solution. See mole.

mole (symbol: M). Amount of substance that has a weight in grams numerically equal to the molecular weight of the substance. Also called gram molecular weight. A mole contains 6.023 × 1023 molecules or atoms of a substance.

molecular biology  The area of knowledge concerned with the molecular aspects of organisms and their cells.

molecular cloning  The biological amplification of a specific DNA sequence through mitotic division of a host cell into which it has been transformed or transfected. See cloning.

molecular genetics  The area of knowledge concerned with the genetic aspects of molecular biology, especially with DNA, RNA and protein molecules.

molecule (L. diminutive of moles, a little mass)  A unit of matter, the smallest portion of an element or a compound that retains chemical identity with the substance in mass. The molecule usually consist of a union of two or more atoms; some organic molecules containing a very large number of atoms.

monoclonal antibody (mAB) A single type of antibody that is directed against a specific epitope (antigen, antigenic determinant) and is produced by a single clone of B cells or a single hybridoma cell line, which is formed by the fusion of a lymphocyte cell with a myeloma cell. Some myeloma cells synthesize single antibodies naturally.

monocot  See monocotyledon.

monocotyledon  (Gr. monos, solitary + kotyledon, a cup-shaped hollow) A plant whose embryo has one seed leaf (cotyledon). Examples are cereal grains (corn, wheat, rice), asparagus, and lily. Colloquially called a monocot. cf dicotyledon.

monoculture  The agricultural practice of cultivating a single crop on a whole farm or area.

monoecious  Denoting plant species that have separate male and female flowers on the same plant (e.g., maize).

monogastric animals  Animals with simple stomachs that do not ruminate. cf ruminant animals.

monophyletic  Describing any group of organisms that are assumed to have originated from the same ancestor.

monogenic  Controlled by a single gene, as opposed to multigenic.

monohybrid   (Gr. monos, solitary + L. hybrida, a mongrel)  The offspring of two homozygous parents that differ from one another by the alleles present at only one locus.

monohybrid cross  A cross between parents differing in only one trait or in which only one trait is being considered.

monolayer  A single layer of cells growing on a surface.

monomer  A single molecular entity that may combine with others to form more complex structures.

monoploid  See haploid.

monosaccharide  A single sugar. cf polysaccharide.

monosomic (n: monosomy)  describing a diploid organism lacking one chromosome (2n -1) of its proper (disomic) complement; a form of aneuploidy. See also disomy.

mono-unsaturates  Oils containing mono-unsaturated fatty acids.

monozygotic twins  One-egg or identical twins; twins derived from the splitting of a single fertilized ovum.

morphogen  A substance that stimulates the development of form or structure in an organism.

morphogenesis  The development, through growth and differentiation, of form and structure in an organism.

morphogenic response  The effect on the developmental history of a plant or its parts exposed to a given set of growth conditions or to a change in the environment.

morphology (Gr. morphe, form + logos, discourse)  1.The science of studying form and its development.

    2. General: Shape, form, external structure or arrangement.

mosaic  An organism or part of an organism that is composed of cells with different origin.

mother plant  See donor plant.

movable genetic element  See transposon.

mRNA; messenger RNA  The RNA transcript of a protein-encoding gene. The information encoded in the mRNA molecule is translated into a polypeptide of specific amino acid sequence by the ribosomes. In eukaryotes, mRNAs transfer genetic information from the DNA to ribosomes, where it is translated into protein.

MRUs  Minimum recognition units. See dabs.

mtDNA  See mitochondrial DNA.

multi-copy  Describing plasmids which replicate to produce many plasmid molecules per host genome, e.g., pBR322 is a multi-copy plasmid, there are usually 50 pBR322 molecules (or copies) per E. coli genome.

multigene family  A group of genes that are similar in nucleotide sequence or that produce polypeptides with similar amino acid sequences.

multigenic  Controlled by several genes, as opposed to monogenic.

multi-locus probe  A probe that hybridizes to a number of different sites in the genome of an organism. See probe.

multimer; multimeric  A protein made up of more than one peptide chain.

multiple alleles  The existence of more than two alleles at a locus in a population.

multiple cloning site  See polylinker.

multiple drop array (MDA)  See microdroplet array.

multiple ovulation and embryo transfer  (MOET)  A technology by which a single female that usually produces only one or two offspring can produce a litter of offspring. Involves stimulation of a female to shed large numbers of ova; natural mating or artificial insemination; collection of fertilized ova (either surgically, or non-surgically through the cervix); and transfer (usually non-surgical, through the cervix) of these fertilized ova to recipient females.

multivalent vaccine  A single vaccine that is designed to elicit an immune response either to more than one infectious agent or to several different epitopes of a molecule.

mutable genes  Genes with an unusually high mutation rate.

mutagen  An agent or process which is capable of inducing a mutation, such as UV light. cf mutation.

mutagenesis  Change(s) in the genetic constitution of a cell through alterations to its DNA.

mutant  An organism or an allele that differs from the wild type because it carries one or more genetic changes in its DNA. A mutant organism may carry mutated gene(s) (= gene mutation); mutated chromosome(s) (= chromosome mutation); or mutated genome(s) (= genome mutation). a.k.a. a variant.

mutation  (L. mutare, to change)  A sudden, heritable change appearing in an individual as the result of a change in the structure of a gene (= gene mutation); changes in the structure of chromosomes (= chromosome mutation); or in the number of chromosomes (= genome mutation). cf genetic diversity; genetic drift.

mutation pressure  A constant mutation rate that adds mutant genes to a population; repeated occurrences of mutations in a population.

mutualism  See symbiosis.

mycelium (pl: mycelia)  Threadlike filament making up the vegetative portion of thallus fungi.

mycoprotein  Fungal protein.

mycotoxin  Toxic substance of fungal origin, such as aflatoxin.

mycorrhiza   (Gr. mykos, fungus + riza, root)  Fungi that form an association with or have a symbiotic relationship with roots of more developed plants.

myeloma  A plasma cell cancer.

myo inositol  See inositol.

myosin  See actin.

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