Multipotent stem cellsStem cells whose progeny are of multiple differentiated cell types, but all within a particular tissue, organ, or physiological system.
multivalent vaccineA vaccine designed to elicit an immune response either to more than one infectious agent or to several different antigenic determinants of a single agent.
mutable geneA gene which has an unusually high rate of mutation.
Mutagen(MYOO-tuh-jen) Anything that causes a mutation (a change in the DNA of a cell).
mutagenesisInduction of heritable change(s) in the genetic constitution of a cell through alterations to its DNA.
MutagenicityThe capacity of a chemical or physical agent to cause permanent genetic alterations. See also: somatic cell genetic mutation
mutantAn organism or an allele bearing a mutation. Usually applied when a characteristic change in phenotype can be recognized.
Mutation(myoo-TAY-shun) Any change in the DNA of a cell. Mutations may be caused by mistakes during cell division, or they may be caused by exposure to…
Mutation breedingCommonly used practices in plant breeding and other areas in which chemicals or radiation are applied to whole organisms, for example plants, or cells so…
mutation pressureA constant mutation rate that adds mutant genes to a population; repeated occurrences of mutations in a population.
Myelin sheath(my' uh lin) the tubular structure that surrounds the nerve fibers.
Myeloid(MY-eh-loyd) Having to do with or resembling the bone marrow. May also refer to certain types of hematopoietic (blood-forming) cells found in the bone…
Myeloid stem cellsPrecursors to the other lines of blood cells: erythrocytes, granulocytes, monocytes, and platelets.
myeloma(MY-eh-LOH-muh) Cancer that arises in plasma cells, a type of white blood cell.
MyoD1A group of four basic myogenic regulatory factors (helix-loop-helix transcription) and a newly discovered factor called muscle enhancer factor-2 which…
narrow-host-range plasmidA plasmid that can replicate in one, or at most a few, different bacterial species.
narrow-sense heritabilityThe proportion of the phenotypic variance that is due to variation in breeding values; the proportion of the phenotypic variance that is due to additive…
National Science Foundation (NSF)A nonregulatory agency which has oversight of biotechnology research activities that the agency funds.
native proteinThe naturally occurring form of a protein.
Natural killer cellA type of white blood cell that contains granules with enzymes that can kill tumor cells or microbial cells.
Natural selectionThe differential survival and reproduc- tion of organisms with genetic characteristics that enable them to better utilize environmental resources.
necrosis(ne-KRO-sis) Refers to the death of living tissues.
negative autogenous regulationInhibition of the expression of a gene or set of co-ordinately regulated genes by the product of the gene or the product of one of the genes.
negative control systemA mechanism by which a regulatory protein is required to turn off gene expression.
negative selectionSelection against individuals possessing a certain character. Opposite: positive selection.
neomycin phosphotransferase II(Abbreviation: npt-II). An enzyme which detoxifies the antibiotic neomycin, used as a marker gene to select for successfully transformed cells in plant…
neoplasm(NEE-oh-PLA-zum) An abnormal mass of tissue that results when cells divide more than they should or do not die when they should.
neotenyThe retention of juvenile body characters in the adult state, or the occurrence of adult characters in the juvenile state.
NestinAn intermediate filament protein found in cells such as neural and pancreatic precursors.
net photosynthesisPhotosynthetic activity minus respiratory activity, measured by the net absorption of carbon dioxide.
Neural crestA band of cells that extend lengthwise along the neural tube of an embryo and give rise to cells that form the cranial, spinal, and autonomic ganglia, as…
Neural plateA thickened band of ectoderm along the dorsal surface of an embryo. The nervous system develops from this tissue.
Neural stem cellA type of stem cell that resides in the brain, which can make new nerve cells (called neurons) and other cells that support nerve cells (called glia).
Neural stem cell (NSC)A stem cell found in adult neural tissue that can give rise to neurons, astrocytes, and oligodendrocytes.
Neural tubeThe embryological forerunner of the central nervous system.
NeuroectodermThe central region of the early embryonic ectoderm, which later forms the brain and spinal cord, as well as evolving into nerve cells of the peripheral…
NeuroepitheliumA specialized epithelial structure that forms the termination of a nerve of a special sense, i.e.
neurofibromatosisAn inherited progressive disorder in which tumors form on peripheral nerves. The tumors can be severely disfiguring and can also result in loss of hearing…
NeuronsNerve cells, the structural and functional unit of the nervous system. A neuron consists of a cell body and its processes-an axon and one or more…
NeurosphereA primitive neural tissue that arises when embryonic stem cells are grown in certain culture conditions.
neutral mutationA mutation that changes the nucleotide sequence of a gene, but has no observable effect on the fitness of the organism.
neutral theoryThe theory that much of evolution has been primarily due to random drift of neutral mutations.
neutropenia(noo-troh-PEE-nee-uh) An abnormal decrease in the number of neutrophils, a type of white blood cell.
neutrophil(NOO-tro-fil) A type of white blood cell.
nickTo break (or a break in) a phosphodiester bond in one of the strands of a double-stranded DNA molecule.
Nick translationA procedure for making a DNA probe in which a DNA fragment is treated with DNase to produce single-stranded nicks, followed by incorporation of…
nicked circleDuring the extraction of plasmid DNA from a bacterial cell, one strand of the DNA often becomes nicked.
Nicked circle (relaxed circle)During extraction of plasmid DNA from the bacterial cell, one strand of the DNA becomes nicked.
Niemann-Pick disease, type C (NPC)A disease that causes progressive deterioration of the nervous system by blocking movement of cholesterol within cells.
nif gene clusterGroup of bacterial genes responsible for the biological fixation of atmospheric nitrogen.
NIHA federal agency in the U.S. that conducts biomedical research in its own laboratories; supports the research of non-Federal scientists in universities…
nitrateThe form of nitrogen that can be used directly by plants; a major component of inorganic fertilizers.
nitrificationThe natural process in which nitrogen in plant and animal wastes is oxidized, first to nitrites and then to nitrates, through the action of soil-borne…
NitrocelluloseA membrane used to immobilize DNA, RNA, or protein, which can then be probed with a labeled sequence or antibody.
nitrogen assimilationThe incorporation of nitrogen into the cells of living organisms.
Nitrogen fixationThe conversion of atmospheric nitrogen to biologically usable nitrates.
Nitrogenous baseThe purines (adenine and guanine) and pyrimidines (cytosine, and thymine or uracil ) that are present in DNA and RNA.
Nitrogenous basesThe purines (adenine and guanine) and pyrimidines (thymine, cytosine, and uracil) that comprise DNA and RNA molecules.
NMDA receptor(N-methyl-d-aspartate receptor). A neurotransmitter receptor for excitatory synapses.
nodal cultureThe culture of a lateral bud and a section of adjacent stem tissue.
nodeAny device connected to network. PCs, servers, and printers are all nodes on the network.
nodularTerm commonly used to describe the pebbly (rough) texture of a callus.
nodulationThe formation of nodules on the roots of legumes following colonization by symbiotic nitrogen-fixing bacteria.
nodule(NOD-yool) A growth or lump that may be cancerous or noncancerous.
non repetitive DNA/RNAA nucleotide sequence which does not include a significant proportion of repetitive sequences of nucleotide s.
non-additive genetic variationThe proportion of the total genetic variation in a population that does not respond to simple mass selection and that causes specific pairwise crosses to…
non-autonomousA term referring to biological units that cannot function by themselves; such units require the assistance of another unit, or "helper".
non-coding DNAThe strand of DNA that does not carry the information necessary to make a protein.
non-directivenessThe process by which genetic counselors advise clients toward a certain test or outcome, particularly related to child-bearing issues, without pressure or…
non-disjunctionFailure of separation of homologous chromosomes or chromatids in mitosis or meiosis, resulting in too many chromosomes in some daughter cells and too few…
Non-Myeloablative ("Mini") Stem Cell TransplantA method used to prime a patient for a stem cell transplant by employing lower doses of chemotherapy and/or radiotherapy to damage the leukemia-producing…