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Natural selection
The differential survival and reproduction of organisms because of differences in characteristics that affect their ability to utilize environmental resources.
Necrosis
Death of tissue evidenced by discolouration, dehydration and loss of organization.
Negative control system
A mechanism by which a regulatory protein is required to turn off gene expression.
Nematode
Slender, unsegmented worms, often parasitic. Also known as eelworm, especially when phytoparasitic.
Neurodegenerative disease
Diseases caused by the irreversible deterioration of essential cell and tissue components of the nervous system.
Neurons
Cells of the nervous system, which transmit nerve impulses (electrical signals) between cells.
Neurotransmitter
A chemical that mediates the transmission of nerve impulses between neurons.
Neutral mutation
A mutation that changes the nucleotide sequence of a gene, but has no observable effect on the fitness of the organism.
Nitrile herbicide
Chemical class of herbicides used for post-emergent control of annual broadleaf weeds. Broken down by soil bacteria.
Non-selective
(In herbicides) Lacking specificity. Lethal to many plant varieties, whether or not they are considered weeds.
Nonsense mutation
A mutation which converts an amino-acid-specifying codon into a stop codon, e.g. a single base change from UAU to UAG generates the premature termination of the polypeptide chain at the position where a tyrosine was incorporated in the wild type.
Non-target organism/species
Organisms that may be exposed to a given product or event, even though they are not the intended target.
Non-transformed
Those cells which failed to incorporate foreign DNA into their genomes during an engineering attempt to add a gene(s).
Nopaline synthase
An enzyme used as a genetic tag.
Novel/novel food
New. In the context of food, the term often refers to genetically modified foods, foods developed using a new process (including the use of genetically modified organisms), or substances that have never been used as foods before.
Novel pollination mechanisms
A process that involves the use of genetic modification to create a unique pollination environment where intentionally selected varieties of a crop must pollinate each other.
Novel traits
A characteristic that has been intentionally selected, created or introduced into a distinct, stable population of the same species (animal or plant) through a specific genetic change.
Nuclear transfer
A technology by which novel animals are generated by cloning a single diploid somatic cell. It involves inserting a single diploid cell from a culture of cells into an enucleated ovum. The resultant diploid ovum develops into an embryo that is placed in a recipient female, which gives birth to the cloned animal in the normal manner. Note that the term is somewhat of a misnomer, since it is a whole cell that is transferred, not just the nucleus.
Nuclease
A class of largely bacterial enzymes that degrade DNA or RNA molecules by catalysing the cleavage of the phosphodiester bonds that link adjacent nucleotides. For deoxyribonuclease (DNAse) the substrate is DNA, for ribonuclease (RNAse) the substrate is RNA, and for S1 nuclease, the substrate is single-stranded DNA or RNA. Endonucleases cleave at internal sites in the substrate molecule, while exonucleases progressively cleave from the end of the substrate molecule. Nucleases have varying degrees of base-sequence specificity, the most specific being the restriction endonucleases.
Nucleic acid
A macromolecule consisting of polymerized nucleotides. Two forms are found, DNA and RNA. Nucleic acids may be linear or circularized, and single- or double-stranded.
Nucleolus
An RNA-rich nuclear organelle in the nucleus of eukaryotic cells, produced by a nucleolar organizer. It represents the storage place for ribosomes and ribosome precursors. The nucleolus consists primarily of ribosomal precursor RNA, ribosomal RNA, their associated proteins, and some, perhaps all, of the enzymatic equipment (RNA polymerase, RNA methylase, RNA cleavage enzymes) required for synthesis, conversion and assembly of ribosomes. Subsequently the ribosomes are transported to the cytoplasm.
Nucleoplasm
The non-staining or slightly chromophilic, liquid or semi-liquid, ground substance of the interphase nucleus and which fills the nuclear space around the chromosomes and the nucleoli. Little is known of the chemical composition of this ground substance, which is not easily defined. Sometimes called "karyoplasm" when it is gel-like, and "karyolymph" when it is a colloidal fluid.
Nucleoside
A base (purine or pyrimidine) that is covalently linked to a 5-carbon (pentose) sugar. When the sugar is ribose, the nucleoside is a ribonucleoside; when it is 2-deoxyribose, the nucleoside is a deoxyribonucleoside.
Nucleotide
A nucleoside with one or more phosphate groups linked at the 3'- or 5'-hydroxyl of a pentose sugar. When the sugar is ribose, the nucleotide is a ribonucleotide; when it is 2-deoxyribose, the nucleotide is a deoxyribonucleotide. RNA and DNA are polymers of, respectively, ribonucleoside 5'-monophosphates and deoxyribonucleoside 5'-monophosphates. Nucleotides containing the bases adenine, guanine and cytosine (A, G, C) occur in both DNA and RNA; thymine (T) occurs only in DNA, and uracil (U) only in RNA. Ribonucleoside mono-, di-, and triphosphates for which a specific base is not assigned are abbreviated NMP, NDP, and NTP, while deoxyribonucleoside mono-, di-, and tri-phosphates are abbreviated dNMP, dNDP, and dNTP. Otherwise, the "N" is replaced by the base letter abbreviation.
Nucleus
A dense protoplasmic membrane-bound region of a eukaryotic cell that contains the chromosomes, separated from the cytoplasm by a membrane; present in all eukaryotic cells except mature sieve-tube elements and red blood cells.
Source: United Nations Food and Agriculture Organization
