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ICSI  See intracytoplasmic sperm injection.

identical twins  See monozygotic twins.

ideogram  See karyogram.

illuminate  To supply or brighten with light. Illumination is an absolute requirement for tissue cultures. Fluorescent lights are commonly employed. The light intensity is dependent on the light source and the requirements of the culture.

imaginal disc  A mass of cells in the larvae of Drosophila and other holometabolous insects that gives rise to particular adult organs, such as antennae, eyes or wings.

imbibition (L. imbibere, to drink)  1. The absorption of liquids or vapours into the ultramicroscopic spaces or pores found in materials.

    2. The initial water uptake by seeds starting germination.

immediate early gene  A viral gene that is expressed promptly after infection.

immobilized cells  Cells entrapped in matrices such as alginate, polyacrylamide and agarose designed for use in membrane and filter bioreactors.

immortalization  The genetic transformation of a cell type into a cell line which can proliferate indefinitely.

immortalizing oncogene  A gene that upon transfection enables a primary cell to grow indefinitely in culture.

immune response  The processes, including the synthesis of antibodies, that are used by vertebrates to respond to the presence of a foreign antigen. See primary immune response; secondary immune response.

immunity  The state of relative insusceptibility of an animal or plant to infection by disease-producing organisms or to the harmful effects of their poisons.

immunization  The production of immunity in an individual by artificial means. Active immunization involves the introduction, either orally or by infection, of specially treated bacteria, viruses or their toxins so as to stimulate the production of antibodies.

immuno-affinity chromatography  A purification technique in which an antibody is bound to a matrix and is subsequently used to bind and separate a protein from a complex mixture. cf affinity chromatography.

immunoglobulin  One of a group of proteins (globulins) in the body that act as antibodies. They are produced by specialized cells (B lymphocytes) and are present in blood serum and other body fluids.

immunosuppression  The suppression of immune response. Immunosuppression is necessary following organ transplants in order to prevent the host rejecting the grafted organ.

immunoassay; immunodiagnostics  An assay system which detects proteins by using an antibody specific to that protein. A positive result is seen as a precipitate of an antibody-protein complex. The antibody can be linked to a radioactive atom or to an enzyme which catalyses an easily monitored reaction such as a change in colour.

immunochemical control  Use of immune agents to combat infections.

immunodiagnostics  See immunoassay.

immunogen  See antigen.

immunogenicity  The ability to elicit an immune response.

immunosensor  A biosensor having an antibody as biological part.

immunosuppressor  A substance, an agent or a condition that prevents or diminishes the immune response.

immunotherapy  The use of an antibody or a fusion protein containing the antigen binding site of an antibody to cure a disease or enhance the well-being of a patient.

immunotoxin  Protein drugs consisting of an antibody joined to a toxin molecule. Immunotoxins can be made by linking toxin and antibody molecules chemically, or by fusing the genes for the toxin and the antibody. The antibody portion of the molecule facilitates binding to a target molecule or cell, and the toxin inactivates or kills the target molecule or cell.

impeller  An agitator that is used for mixing the contents of a bioreactor.

inactivated agent  A virus, bacterium or other organism that has been treated to prevent it from causing a disease.

inbred line  The product of inbreeding, i.e., the mating of individuals that have ancestors in common; in plants and laboratory animals, it refers to populations resulting from at least 6 generations of selfing or 20 generations of brother-sister mating, that are for all practical purposes, completely homozygous. In farm animals, the term is sometimes used to describe populations that have resulted from several generations of the mating of close relatives, without having reached complete homozygosity.

inbreeding  Matings between individuals that have one or more ancestors in common, the extreme condition being self-fertilization, which occurs in many plants and some primitive animals.

inbreeding depression  Reduction in vigour, yield, etc., of a population that is commonly seen as the level of inbreeding increases. The traits that show greatest inbreeding depression are those that are most closely associated with viability and reproductive ability.

inclusion body  Protein that is overproduced in a recombinant bacterium and forms a crystalline array inside the bacterial cell.

incompatibility  1. Selectively-restricted mating competence, which limits fertilization, such as lack of proper functions by otherwise normal pollen grains or certain pistils, a condition that may be caused by a variety of factors.

    2. A physiological interaction resulting in graft rejection or failure.

    3. A function of a related group of plasmids. Plasmids which are closely related share similar replication functions and this leads to the exclusion of one or the other plasmid if they are present in the same cell; thus such plasmids are incompatible. Plasmids are placed in incompatibility groups by this simple reaction and, in general, plasmids belonging to one incompatibility group (q.v.) are very closely related.

incompatibility group  A classification scheme indicating which plasmids can co-exist within a single cell. Plasmids must belong to different incompatibility groups to co-exist within the same cell. Plasmids that belong to the same incompatibility group are unstable when placed in the same cell. A plasmid cloning vector should always belong to an incompatibility group different from that of the host bacterium's endogenous plasmids.

incomplete digest  See partial digest.

incomplete dominance  A type of gene action in which heterozygotes have a phenotype that is distinctly different from, and intermediate to, the homozygous phenotypes. See heterozygote; phenotype.

incomplete penetrance  When some individuals in a population have a specific genotype that causes an abnormality but are not affected.

incubation (L. incubare, to lie on)  1. The hatching of eggs by means of heat, either natural or artificial.

    2. Period between infection and appearance of symptoms induced by parasitic organisms.

    3. The culture of cells and organisms.

incubator  An apparatus in which environmental conditions (light, photoperiod, temperature, humidity, etc.) are fully controlled, and used for hatching eggs, multiplying micro-organisms, culturing plants, etc. cf culture room; growth cabinet.

indehiscent  Describing a fruit or fruiting body that does not open to release its seeds or spores when ripe.

independent assortment  The random distribution of alleles (from different loci) to the gametes that occurs when genes are located in different chromosomes or far apart on large chromosomes. The distribution of alleles at one locus is independent of other the distribution of alleles at another locus. cf linkage.

indeterminate growth  1. Unlimited growth potential for a definite or indefinite period. Some apical meristems can produce unrestricted numbers of lateral organs.

    2. In legumes, used to describe plant architecture.

indirect embryogenesis  Embryo formation on callus tissues derived from zygotic or somatic embryos, seedling plant or other tissues in culture. cf direct embryogenesis.

indirect organogenesis  Organ formation on callus tissues derived from explants.

inducer  A low-molecular-weight compound or a physical agent that is bound by a repressor so as to produce a complex that can no longer bind to the operator; thus, the presence of the inducer turns on the expression of the gene(s) controlled by the operator.

inducible  A gene or gene-product is said to be inducible if its transcription or synthesis is increased by exposure of the cells to an effector. Effectors are usually small molecules whose effects are specific to particular operons or groups of genes. See constitutive.

inducible enzyme  An enzyme that is synthesized only in the presence of the substrate that acts as an inducer.

inducible gene  A gene that is expressed only in the presence of a specific metabolite, the inducer.

induction  (L. inducere, to lead in)  Act or process of causing to occur; process whereby a cell or tissue influences neighbouring cells or tissues. Turning on transcription of a specific gene or operon. Getting an organism to make a protein by exposing it to some stimulus.

induction media  1. Media used to induce the formation of organs or other structures.

    2. Media causing variation or mutation in the tissues exposed to it.

inembryonation  See artificial inembryonation.

I/E region  See integration-excision region.

inert  A support structure that makes no chemical contribution, and whose only function is support. Physiologically it is a neutral or immobile unit.

infection  The invasion of any living organisms by disease-causing micro-organisms, which proceed to establish themselves, multiply, and produce various clinical signs in their host.

infectious agent  Typically, a proliferating virus, bacterium or parasite that causes a disease in plants or animals.

infiltrate  To force the passage of liquid into tissue pores or space, such as by applying a vacuum, then releasing it, during the disinfectation procedure.

inflorescence (L. inflorescere, to begin to bloom)  1. The way the flowers are arranged on the stalk of a plant.

    2. The flowers of a plant collectively.

    3. The flowering or blooming process.

IGS  Internal guide sequence  See guide sequence.

inhibitor  Any substance or object that retards a chemical reaction; a major or modifier gene that interferes with a reaction or with the expression of another gene.

inheritance  The transmission of particular characteristics and/or genes from generation to generation.

initial  Noun: Cells in a meristem that remain permanently meristematic and form tissues of particular structure and function.

initiation  1. Early steps or stages of a tissue culture process (culture growth, organogenesis, embryogenesis)

    2. Early stages of biosynthesis.

initiation codon; initiator  The codon AUG which specifies the first amino acid methionine of a polypeptide chain. In bacteria, the initiation codon is either AUG, which is translated as n-formyl methionine or, rarely, GUG (valine). In eukaryotes, the initiation codon is always AUG and is translated as methionine. The term is also used to describe the corresponding sequence in DNA, namely ATG. See start codon; initiator codon.

initiation factors  Soluble proteins required for the initiation of translation.

initiator  See initiation codon.

inoculate  Deliberately introduce something into. The process is inoculation. Not the same as contamination.

    1. In bacteriology, tissue culture, etc., placing inoculum into (or onto) medium to initiate a culture.

    2. In immunology, to immunize.

inoculation cabinet  Small room or cabinet for inoculation (of tissue or micro-organism cultures) operations, often with a current of sterile air to carry contaminants away from the work area.

inoculum (pl: inocula)  1. A small piece of tissue cut from callus, or an explant from a tissue or organ, or a small amount of cell material from a suspension culture, transferred into fresh medium for continued growth of the culture. See also minimum inoculum size.

    2. Microbial spores or parts (such as mycelium).

    3. Vaccine.

inorganic compound  A chemical compound that generally is not derived from living processes; compounds that do not contain carbon.

inositol (hexahydroxycyclohexane; C6H6(OH)6)  1. A cyclic acid that is constituent of certain cell phosphoglycerides.

    2. A water-soluble nutrient frequently referred to as a "vitamin" in plant tissue culture. Also acts as a growth factor in some animals and micro-organisms.

inositol lipid  A membrane-anchored phospholipid that transduces hormonal signals by stimulating the release of any of several chemical messengers. See phospholipid.

insecticide  A substance that kills insects.

insert  A DNA molecule that is incorporated into a cloning vector.

insertion element  Generic term for DNA sequences found in bacteria capable of genome insertion. Postulated to be responsible for site-specific phage and plasmid integration.

insertion mutations  Changes in the base sequence of a DNA molecule resulting from the random integration of DNA from another source. See DNA; mutation.

insertion sequence  See IS element.

insertion site; cloning site  A unique restriction site in a vector DNA molecule into which foreign DNA can be inserted. The term is also used to describe the position of integration of a transposon or insertion site element.

in situ  (Latin for "in place")  Meaning in the natural place or in the original place.

    1. Experimental treatments performed on cells or tissue rather than on extracts from them.

    2. Assays or manipulations performed with intact tissues.

in situ colony; in situ plaque hybridization  A procedure for screening colonies or plaques growing on plates or membranes for the presence of specific DNA sequences by the hybridization of nucleic acid probes to the DNA molecules present in these colonies or plaques.

in situ conservation  A conservation method that attempts to preserve the integrity of genetic resources by conserving them within the evolutionary dynamic ecosystems of their original habitat or natural environment. cf ex situ conservation.

in situ conservation of farm animal genetic diversity  In AnGR: All measures to maintain live animal breeding populations, including those involved in active breeding programmes in the agro-ecosystem where they either developed or are now normally found, together with husbandry activities that are undertaken to ensure the continued contribution of these resources to sustainable food and agricultural production, now and in the future. (Source: FAO, 1999)

in situ plaque hybridization  See in situ colony.

instability  A random-type variation or a lack of steadiness. Due to genetic instability, cell lines lose certain characteristics or functions in culture.

insulin  A peptide hormone secreted by the Langerhans islets of the pancreas, and that regulates the level of sugar in the blood.

integrating vector  A vector that is designed to integrate cloned DNA into the host cell chromosomal DNA.

integration  The recombination process which inserts a small DNA molecule (usually by homologous recombination) into a larger one. If the molecules are circular, integration involves only a single crossing-over; if linear, then two crossings-over are required. A well known example is the integration of phage l (lambda) DNA into the E. coli genome.

integration-excision (I/E) region  The portion of bacteriophage lambda (l) DNA that enables bacteriophage lambda (l) DNA to be inserted into a specific site in the E. coli chromosome and excised from this site.

integument  One of the layers that enclosed the ovule, and is the precursor of the seed coat.

intensifying screen  A plastic sheet impregnated with a rare-earth compound, such as calcium tungstate, which absorbs ß radiation and emits light. When placed on one side of a piece of X-ray film with a radioactive sample on the other side, the intensifying screen will capture some of the ß emissions which pass through the film, blackening the X-ray film and so greatly enhancing the sensitivity of the detection. An intensifying screen is used in Southern and northern blotting procedures.

interaction  In statistics, an effect that cannot be explained by the additive action of contributing factors; a departure from strict additivity.

intercalary   (L. intercalare, to insert)  Meristematic tissue or growth not restricted to the apex of an organ, i.e., growth at nodes.

intercalary growth  A pattern of stem elongation typical of grasses. Elongation proceeds from the lower internodes to the upper internodes through the differentiation of meristematic tissue at the base of each internode.

intercalating agent  A chemical capable of inserting between adjacent base pairs in a DNA molecule.

intercellular space  Pore space between cells, especially typical of leaf tissues.

interfascicular cambium  Cambium that arises between vascular bundles.

interference  Crossing over at one point that alters the chance of another crossing-over nearby; detected by studying the pattern of crossings-over with three or more linked genes. Interference is positive or negative depending on whether the chance of another crossing-over nearby is reduced or increased, respectively.

interferon  A family of small proteins that stimulate viral resistance in cells.

intergeneric  A cross between two different genera.

intergenic regions  DNA sequences located between genes; they comprise a large percentage of a genome and have no known function.

interleukin  A group of proteins that transmit signals between immune cells and are necessary for mounting normal immune responses.

internal guide sequence (IGS)  See guide sequence.

intervening sequence  See intron.

internode (L. inter, between + nodus, a knot)  The region of a stem between two successive nodes.

interphase  The stage in the cell cycle when the cell is not dividing; the stage follows telophase of one division and extends to the beginning of prophase in the next division. DNA replication occurs during this stage.

intersex  An organism displaying a mixture of male and female attributes.

interspecific  Between two different species, e.g., an interspecific cross is a cross between two species.

intervening sequence  See intron.

intracellular  (L. intra, within + cell)  Occurring within a cell.

intracytoplasmic sperm injection (ICSI)  The injection, using micromanipulation, of a single sperm into the cytoplasm of a mature oocyte.

intrageneric  Within a genus, such as a hybrid resulting from a cross between species within one genus.

intragenic complementation  Complementation that occurs between two mutant alleles of a gene; common only when the product of the gene functions as a homomultimer.

intraspecific  Within a species or its populations, including subspecies, such as an intraspecific cross, or variation.

introgression  The introduction of new gene(s) into a population by crossing between two populations, followed by repeated backcrossing to that population while retaining the new gene(s).

intron; intervening sequence  A segment of DNA sequence of a eukaryotic gene, not represented in the mature (final) mRNA transcript, because it is spliced out of the primary transcript before it can be translated; a process known as intron splicing. Some genes of higher eukaryotes contain a large number of introns, which make up the bulk of the DNA sequence of the gene. Introns are also found in genes whose RNA transcripts are not translated, namely eukaryotic rRNA and tRNA genes. In these cases the intron sequence does not appear in the functional RNA molecule. cf exon.

invariant  Constant, unchanging; usually referring to the portion of a molecule that is the same across species.

invasiveness  Ability of a plant to spread beyond its introduction site and become established in new locations, where it may have a deleterious effect on organisms already existing there.

inversion  A chromosome re-arrangement that reverses the order of a linear array of genes in it.

inverted repeat  Two regions of a nucleic acid molecule which have the same nucleotide sequence but in an inverted orientation, such as

      5´ GCACTTG... ...CAAGTGC 3´
      3´ CGTGAAC... ...GTTCACG 5´

    Because they contain exactly the same message when read in either direction, inverted repeats are said to be palindromes.

in vitro (L. for "in glass")  Living in test tubes, outside the organism or in an artificial environment, typically in glass vessels in which cultured cells, tissues, organs or whole plants may reside.

in vitro embryo production (IVEP)  The combination of ovum pickup (q.v.), in vitro maturation (q.v.) of ova, and in vitro fertilization (q.v.). A potential means of overcoming the variability between donors in number of ova collected in embryo-transfer programmes.

in vitro fertilization (IVF)  A widely used technique in human and animal science, whereby the egg is fertilized with sperm outside the body. Usually, the fertilized egg is cultured outside the body for a few days (to confirm that fertilization has occurred) before re-implantation into a female.

in vitro maturation (IVM)  Culture of immature ova in the laboratory, usually until they are ready for in vitro fertilization.

in vitro mutagenesis  See directed mutagenesis.

in vitro transcription; cell-free transcription  The specific and accurate synthesis of RNA in the test tube using purified DNA preparations as a template. So-called "coupled systems" may be obtained from E. coli which carry out both mRNA synthesis and its translation into protein. For eukaryotes, separate cell-free systems have to be set up to demonstrate the activity of the three functionally distinct RNA polymerase complexes.

in vitro translation; cell-free translation  The synthesis of proteins in the test-tube from purified mRNA molecules using cell extracts containing ribosomal sub-units, the necessary protein factors, tRNA molecules and aminoacyl tRNA synthetases, ATP, GTP, amino acids and an enzyme system for re-generating the nucleoside triphosphates. Prokaryotic translation systems are usually prepared from E. coli or the thermophilic bacterium, Bacillus stearothermophilus. Eukaryotic systems usually employ rabbit reticulocyte lysates or wheat germ.

in vivo  (L. for "in living")  The natural conditions in which organisms reside. Refers to biological processes that take place within a living organism or cell under normal conditions.

in vivo gene therapy  The delivery of a gene or genes to a tissue or organ of an individual to alleviate a genetic disorder.

ion A charged particle.

ion channel  An integral protein within a cell membrane, through which selective ion transport occurs.

ionic bonds  Attractions between oppositely charged chemical groups.

ionizing radiation  The portion of the electromagnetic spectrum that results in the production of positive and negative charges (ion pairs) in molecules. X-rays and gamma rays are examples of ionizing radiation.

IPTG (Isopropyl-b-d-thiogalactopyranoside)  An inducer of the lac (lactose) operon. In recombinant DNA technology, IPTG is often used to induce cloned genes that are under the control of the lac repressor-lac promoter system.

irradiation  (L. in, into + radius, ray)  1. Exposure to any form of radiation.

    2. Treatment with a ray, such as ultraviolet rays, etc.

    3. Apparent enlargement of objects, due to difference in illumination.

    4. In food technology: exposure of food to controlled low levels of ionizing radiation to sterilize or disinfest it, without inducing radioactivity in the target. If in sealed containers, the product is sterile and can be stored under ambient conditions. Used for continuous flow disinfestation of grain at unloading facilities.

IS element (insertion sequence)  A short (800-1400 nucleotide pairs) DNA sequence found in bacteria that is capable of transposing to a new genomic location; other DNA sequences that are bounded by IS elements may also be transposed.

isoalleles  Different forms of a gene that produce the same phenotype or very similar phenotypes.

isochromosome  A chromosome with two identical arms and identical genes. The arms are mirror images of each other.

isodiametric Term commonly used to describe cells with equal diameters.

iso-electric focusing gels  Variant of DNA gel electrophoresis, which separates macromolecules on the basis of their iso-electric point rather than their size.

iso-enzyme  See isozyme.

isoform  A member of a family of closely related proteins that have some amino acid sequences in common and some different.

isogamy  Sexual reproduction involving the production fusion of gametes that are similar in size and structure.

isogenic stocks  Strains of organisms that are genetically identical; completely homozygous.

isolating mechanism  Any of the biological properties of organisms that prevent interbreeding (and therefore exchange of genetic material) between members of different species that inhabit the same geographical area.

isolation medium  An optimum medium suitable for explant survival, growth and development.

isoleucine  See amino acid.

isomerase  Any of a class of enzymes that catalyse the re-arrangement of the atoms within a molecule, thereby converting one isomer into another.

iso-osmotic  See isotonic.

isotonic; iso-osmotic  Solutions having the same osmotic potential; the same molar concentration. For protoplasts to survive, the medium they are suspended in must be isotonic with them.

isotope  One of two or more forms of an element that have the same number of protons (atomic number) but differing numbers of neutrons (mass numbers). Radioactive isotopes are commonly used to make DNA probes and metabolic tracers.

isozyme  A variant of a particular enzyme. In general, all the isozymes of a particular enzyme have the same function and sometimes the same activity, but they differ in amino-acid sequence. With the help of isozyme analysis, based on electrophoresis techniques that can separate the different variants, related species or cultivars can be distinguished.

IVEP  See in vitro embryo production.

IVF  See in vitro fertilization.

IVM  See in vitro maturation.

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