Ifgene - International Forum for Genetic Engineering

Glossary of genetics and genetic engineering with key to abbreviations


See also glossaries at FAO AgBiotech Glossary and  http://www.genome.gov/glossary.cfm


ACNFP: UK Advisory Committee on Novel Foods and Processes.

ACRE: UK Advisory Committee on Releases into the Environment

Adaptive mutation: Bacteria and yeast cells in the stationary (non-growing) phase, have a way of producing (or keeping) only the mutations most approptiate for their making use of new substrates for growth.

Adenosine deaminase deficiency: A lack of an enzyme called adenosine deaminase . Its main characteristic is corresponding lack of immune defences against infection. Sufferers die shortly after birth unless kept in a germ-free environment ('bubbles').

Adenoviruses: a class of viruses amongst which is are the viruses responsible for the common cold.

Allele: Any of the alternative genes which may occupy corresponding positions (loci) on each chromosome of a pair. A mutation, such as one which may be responsible for genetic disease, is an allele.

Allergen: A substance which provokes a hypersensitive reaction in the body.

Amino acid: The structural unit of a protein. There are varying amounts of 20 possible amino acids in different proteins.

Amniocentesis: The most widely used technique of prenatal diagnosis from the 12th week of pregnancy onwards. A small quantity of fluid is removed for analysis from the fluid surrounding the developing fetus.

Anther: The male pollen-bearing part of the flower.

Attenuated vectors: Micro-organisms or pieces of DNA such as plasmids which have certain infective components removed by recombinant DNA technology to destroy their virulence, thereby making them safer to use.

Autosome: In the human being, any one of the 22 matched pairs of chromosomes. One in each pair is inherited from the mother, the other from the father.


Bacteria: Bacteria are microscopic single-celled infectious organisms. Many are harmless, but some cause diseases, eg Mycobacterium tuberculosis which causes tuberculosis.

Bacteriophage: Any viruses that infect bacteria, also known as phage.

Base: the nitrogen-containing components of the DNA molecule. There are four types of bases known as adenine (A), guanine (G), thymine (T) and cytosine (C). The sequence of bases determines the genetic code. Three bases code for each amino acid in a protein.

Biodiversity: The diversity of variety, species, families, genera etc of living organisms in a particular place.

Biodynamic agriculture: An organic farming system which treats the earth as a living organism in the context of the whole cosmos. It is therefore a holistic approach which works not only with soil, weather and seasons, as external factors, but also with the movements of planetary bodies, in particular the moon against the background of the stars. The farms are treated as individualities and as far as possible as self-contained units in that external inputs are kept to an absolute minimum if not zero. This is the most rigorous definition possible for a sustainable agriculture. It includes the development of local breeds and varieties suited to the natural conditions of a locality and to biodynamic farming practices. (for more information see Biodynamic Farming and Gardening Association USA or Biodynamic Agricultural Association (UK))

Bioremediation: Cleaning up waste or polluted land, waters etc using living organisms.

Biotechnology: the industrial use of biological processes.


Carrier: A healthy individual who has both an abnormal and a normal copy of a pair of genes for a genetic disorder or character or characteristic or trait. A carrier of a gene for a recessive disorder will usually remain unaffected through life.

Cell: The smallest structural unit of all living organisms that is able to grow and reproduce independently; a cell is formed of a mass of living material surrounded by a membrane and contains a nucleus. Cells can be classified as germ-line (sperm, eggs) or somatic (rest of body tissues).

Cell line: A culture of cells which can be kept alive indefinitely through the appropriate supply of nutrients.

Chorionic villus sampling (CVS): A small piece of tissue from part of the placenta which shared the genetic make up of the fetus is removed for prenatal diagnosis.

Chromosome: A microscopic particle containing thousands of genes (DNA) found in the nucleus of the cell. The human being has 23 pairs of chromosomes in each somatic body cell. 22 are matching (homologous) pairs called autosomes. The two remaining are sex chromosomes: in females two X chromosomes, in males an X and a Y chromosome. One chromosome of each pair plus one sex chromosome come from the mother, the other 23 from the father. Each chromosome is a double strand of DNA packaged in protein.

Chymosin: one of the enzymes which causes milk to clot and turn into curds and whey during cheese making.

Clone: 1) A group of cells that have descended from one parent cell. 2) Genetically identical organisms that have descended from one parent. 3) Identical sequences of DNA (genes) that have been produced by bacteria or other organisms.

Cloning: The process of creating a clone.

Code: the sequence of DNA bases which forms the instructions for a given characteristic or trait.

Congenital: Present at birth.

Conjugation: The 'mating' process in bacteria which requires cell-to-cell contact being established, and in which genes are transferred between cells.

Cultivar: A crop plant.

Cystic fibrosis: In the UK the most common single genetic disability affecting about 1 in 2000 children. The genetic defect results in the production of abnormally thick mucus. The mucus obstructs the airways of the lung and leads to recurrent lung damage, and it obstructs glands of the intestine and leads to impaired digestion and absorption of food. The disorder requires lifelong treatment to combat infection and to enhance nutrition. Its genetic inheritance is recessive.

Cytoplasm: The part of the cell outside the nucleus.


Deoxyribose: a constituent of DNA

Differentiation: A process of development whereby properties of a cell or tissue become specialised for its particular task.

Diploid: the presence of two chromosomes of a pair in a cell.

Directed Mutation: see Adaptive Mutation

DNA: Deoxyribonucleic acid, a large molecule that contains all genetic information in the cell.

DNAse: Enzyme that breaks down DNA.

DNA polymerase: An enzyme that makes DNA in the presence of a DNA primer and a mixture of the four nucleotides.

DNA primer: A short stretch of DNA needed to start the DNA polymerase reaction.

Dominant gene or allele: Most genes in the human body come in pairs. The pair's members can have codes which match each other or be different. If they are different, one is usually dominant, the other is described as 'recessive'. This means that it is this gene which is expressed in the phenotype (eg the gene implicated in Huntington's disease).

Double-helix: the physical structure of DNA, comprising two parallel strands of DNA coiled helically.

Down's syndrome: A genetic disability in which characteristic physical features are accompanied by learning difficulty. The disorder is the consequence of a chromosome abnormality and is often called trisomy-21 because most commonly there is an additional copy of chromosome 21 present.

Duchenne muscular dystrophy: A single gene disorder which affects 1 in 5000 boys. The condition produces progressive weakness of proximal muscles, beginning in early childhood. Most affected children become chairbound before adulthood. The inheritance is X-linked i.e. it is transmitted from heterozygous females who are unaffected and are described as carriers, to sons who are affected, and to daughters who, like their mothers, are unaffected carriers.


Embryo: Early developmental stage of a plant or animal after fertilisation.

Entelechy: That which makes something, e.g. an organism, what it is. The essence of a thing, organism.

Endogenous: Inside, internal, within.

Enzyme: A protein which speeds up the rate of a chemical reaction or helps a reaction which would not take place at the given conditions to take place. It is itself not permanently changed by taking part in the reaction. (Often described as a biological catalyst)

Epigenetic factors: Factors having an influence on the form, function or behaviour of an organism but originating outside the genome.

Epistasis: Interaction between genes.

ESTs: (expressed sequence tags) Markers for parts of the genome which are known to be expressed in RNA or protein and which are used in mapping the genome.

Eugenics: Deliberate manipulation of the genetic makeup of human populations, traditionally by selective birth control, infanticide, mass murder, genocide. Genetic engineering offers now opportunities for the eugenicist including genetic screening, in vitro fertilisation plus preimplantation screening, germ line genetic modification etc. Eugenic ideas can be traced to the ancient Greek philosopher Plato, but are more recently associated with Nazi Germany and Hitler.    

Eukaryote: The major class of living things including all multicellular, higher organisms and some single-celled organisms that have a nucleus in their cells containing the, chromosomes.

Exogenous: Outside, external, without.

Expression: (of a gene) The central dogma of molecular biology says that genes (DNA) are transcribed into a message (RNA) which is translated into a polypeptide or protein, which in turn gives structural and functional features to a cell.


Factor VIII: One of the many protein components of the blood clotting mechanism which is missing in haemophilia A.

Foetus: Fully developed embryo in womb.

F1 hybrid: First generation after a hybrid has been formed.


Gamete: A reproductive or 'sex' cell: sperm in males, ova in females. It carries inherited characteristics from parent to offspring.

Gel electrophoresis: Analytical tool to separate substances, eg DNA fragments, from each other by having them move through a gel driven by an electric field.

Gene: the so-called biological unit of inheritance; a segment of DNA which provides the genetic information necessary to make one protein or polypeptide.

Gene amplification: The process whereby genes or a sequence of DNA in the genome is greatly increased in number of copies.

Gene cloning: The technique of making many copies of a gene.

Gene expression: the production by a cell of the protein or polypeptide for which the specific gene codes.

Gene pair: Corresponding genes in each of a pair of matching (homologous) chromosomes.

Gene pool: A term used to describe all the genes at a given locus in the population. The size of the pool is related to the genetic diversity in the population.

Genera: Plural of genus, a group of similar species.

Gene silencing: The process(es) whereby certain genes in the genome are prevented from being expressed by chemical modifications and other means.

Gene stacking: Accumulation of several advantageous traits in an organism, usually considered in the context of herbicide tolerance genes in plants (weeds).

Gene therapy: Correcting the genetic make-up of a patient by adding the correct genes in a form which will be expressed, either to the somatic tissues which are affected (eg cystic fibrosis) or to the germ line cells (egg or sperm, currently illegal).

Genetic code: The code establishing the correspondence between the sequence of bases in nucleic acids (DNA and the complementary RNA) and the sequence of amino acids in proteins.

Genetic determinism: Determinism is the doctrine that all acts, choices and events are the inevitable consequence of antecedent sufficient causes. Genetic determinism is the doctrine that the organism is the inevitable consequence of its genetic makeup, or the sum of its genes.

Genetic engineering: The manipulating of genetic material in the laboratory. It includes isolating, copying and multiplying genes, recombining genes or DNA from different species, and transferring genes from one species to another, bypassing the reproductive process.

Genetic disability, disorder or disease: Afflictions which can be associated with what some class as defects in a person's genetic inheritance. They may involve changes (mutations) in single genes or in whole chromosomes, parts of which may be lost, duplicated or placed in the wrong position; or from the interaction of multiple genes and external factors in fetal development. Later in life such interactions seem to be the basis of many of the common serious disorders, such as heart disease, diabetes and cancer, although these are not usually thought of as gene disorders.

Genetic fingerprinting: a technique which enables genetic relationships between close relatives, or the identity of individuals to be established - usually beyond reasonable doubt.

Genetic map: The body of information on the relative positions of genes on chromosomes. Much of the effort of the Human Genome Project is directed to mapping chromosomes.

Genetic marker: A harmless variable inherited change in DNA or protein that can be used to locate a diseased gene on a particular chromosome. Any segment of DNA that can be identified, or whose chromosomal location is known, so that it can be used as a reference point to map or locate other genes. Any gene which has an identifiable phenotype that can be used to track the presence or absence of other genes on the same piece of DNA transferred into a cell.

Gene therapy: The genetic modification of body cells of an individual patient, directed at alleviating disease in that patient.

Genetic inheritance: the transfer of genetic instructions for different characteristics, such as the colour and size of the cell or organism, to successive generations, via reproduction.

Genetic modification: A technique where individual genes can be copied and transferred to another living organism to alter its genetic make up and thus incorporate or delete specific characteristics into or from the organism. The technology is also referred to as genetic engineering, genetic manipulation and gene technology.

Gene: A biological unit of inheritance; a segment of DNA which provides the genetic information necessary to make one protein.

Genome: The totality of genes in an organism

Genotype: A characteristic of an organism is said to have two aspects: genotype and phenotype. Genotype is the make up of the gene itself - its code. The precise variant(s) of the gene(s) carried by an individual.

Genus: A group of similar species.

Germ line: Sperm and egg cells (ova) and their precursors.

Germ line gene therapy: Used to describe genetic modification or 'therapy' of the sex cells (sperm, ova & their precursors). It is banned in the UK.

GMO: (genetically modified organism) An organism changed by genetic engineering. Often now called 'a transgenic'

Growth hormone: a protein, produced by the pituitary gland that promotes growth of the whole body.

GTAC: Gene therapy advisory committee.


Herbicide: a chemical compound used to kill weeds.

Haemoglobin: The red oxygen carrying pigment of the blood. Haemoglobin incorporates two pairs of polypeptides called globins. Various gene mutations which affect the kinds of globins made, or their amounts, can result in diseases called the haemoglobinopathies, notably thalassaemias and sickle cell disease.

Haemophilia: A single gene disorder, which affects about 1 in 1000 males, in which there is defective production of a protein that is necessary for blood clotting and thereby prevents excessive bleeding. Its inheritance is X-linked, i.e. the gene is on the X chromosome.

Haploid: Used to describe a cell having half the usual number of chromosomes, eg sperm and ova.

Herman the Bull: A Dutch bull engineered to contain the human lactoferrin gene which codes for the protein lactoferrin used in the treatment of sepsis. Human lactoferrin is produced in the milk of cows bred from this bull. (Said to be named after Herman de Boer the managing director of Gene Pharming, Holland)

Heterozygous: An organism is described as heterozygous when it has inherited unlike alleles of a specific gene pair from its parents.

Heterozygote An individual who has two different alleles of a gene.

HFEA: UK Human Fertilisation and Embryology Authority

Homozygous: An organism is described as homozygous when it has inherited alleles of a specific gene pair which are the same.

Homozygote An individual who has two identical allells of the gene.

Horizontal gene transfer: Transfer of genes from one individual to another, of the same or different species, usually by means other than cross-breeding. Said to have happened naturally in evolution and can now be done artificially.

Hormone: A chemical messenger which circulates in the blood, eg insulin, sex hormones.

HUGO: Human Genome Organisation, responsible for the Human Genome Project

Huntington's disease: A single gene disorder which affects about 1 in 2000 people and in which, during adult life, there is worsening involuntary movement, accompanied by progressive dementia. It is inherited as a dominant characteristic.

Hybrid: the progeny of a cross between parents of different genetic types or different species.


Iatrogenic: Created by a medical doctor.

Insulin: A protein hormone secreted into the blood from the pancreas and which is involved in controlling, amongst other things, the amount of sugar in the blood.

Interrupted genes: Genes whose coding sequence is interrupted at intervals by long stretches of non-coding sequences. The coding regions came to be known as exons and the non-coding regions as introns. This structure is now found to be characteristic of most eukaryotic genes. The number and size of introns vary greatly, and they are often much longer than the coding sequences. After transcription, the intron regions are removed, or spliced out form the RNA transcript before it is translated into protein.

Intracytoplasmic: Into the cytoplasm, the part of the cell outside the nucleus.

In vitro: Used to describe a biological process conducted outside the body of a living organism. Literally 'in the glass', as in a test-tube.

In vivo: Describes biological processes happening in a living organism.

IVF: In vitro fertilisation.


Jumping genes: More correectly called transposons or mobile genetic elements which can move round genomes and, assisted by suitable carriers, transfer between organisms.



Liposome: Mocroscopic particle of lipid (fat or oil).

Locus: In genetics the place on a chromosome which is occupied by a gene. Plural: loci.


Malformation: A fault in the primary development of an organ or tissue, and therefore present at birth.

Meiosis: The form of cell division (splitting) by which gametes (sperm, ova) are formed. It is described as a reduction division, the gametes each receiving only one of each pair of chromosomes, the haploid state.

Messenger RNA: The RNA intermediate in protein synthesis containing a transcribed copy of the gene sequence that specifies the amino acid sequence of the polypeptide it encodes.

Metabolism: The sum total of the chemical processes that take place in living organisms. resulting in growth, development, and all other forms of energy transformation.

Metabolite: One particular chemical intermediate generated in metabolism.

Micro-organism: a microscopic organism

Mitochondria: Small structures in living cells which are found outside the nucleus and which contain a small number of the cell's genes. Mitochondria are often described as the 'power house of the cell'. They carry their own complement of DNA and are replicated independently so that when the cell divides, each daughter cell will receive half of the mitochondria.

Mitosis: Cell division of somatic cells. Each daughter cell receives both chromosomes of each pair, the diploid state.

Mobile Genetic Element, also called Transposon or Transposable Genetic Element: A sequence of DNA that can move (transpose) from one place to another in the genome of a cell.

Molecule: The smallest unit of any chemical substance which can have an independent separate existence and still retain the properties of that substance; it is composed of atoms bonded together.

Molecular biology: The study of proteins and nucleic acids, substances that make up the living world, their structures and their relationships to biochemical activity; and the substances that are the repositories of genetic information and the agencies for its communication from one generation to the next.

Monoculture: Growing the same crop over a large area year after year.

Multigene families: Genes that exist in multiple copies in the genome. from several copies to many thousands or hundreds of thousands of copies.

Mutagen: A substance or agent that causes genetic mutations, or chemical alteration of the genetic material, DNA.

Mutation: A change in the genetic code (DNA) in a particular gene. A gene which has undergone a mutation is called a mutant; so also is an organism in which the mutant gene is expressed.


Nucleotide: A building block of DNA containing a base.

Nucleus: The place in the cell containing the chromosomes. A structure in the eukaryote cell bounded by a membrane, that contains the genetic material, in the form of DNA organized into chromosomes.


Oncogenes: Genes associated with cancer.

Ooplasmic transplantation: Adding some of the cytoplasm of an ovum from a donor to the ovum of another woman so that the recipient will receive healthy mitochondria. As the mitochondria contain some 30 or so genes the child resulting from the fertilised treated ovum would strictly have 3 genetic parents. By May 2001 some 30 children were reported to have been born by this IVF variant.

Organism: an individual plant, animal or microorganism that can independently carry out all life functions.

Ovulation: Release of egg cell (ovum) from the ovary of an animal.


Patent: Intellectual property protection which gives the owner exclusive right to exploit an invention for a fixed period (e.g 17-20 years) in exchange for full disclosure of how the invention is made.

Pathogen: Any agent that can cause disease.

Phage: A virus which infects bacteria.

Phenotype: How a gene manifests itself as an observable phenomenon (eg a visible characteristic of an organism). The expressed characteristics, or an expressed character of an organism due to its genotype.

Phenylketonuria (PKU): A rare recessive inherited disorder affecting about 1 in 10,000 births in the UK. Affected individuals inherit the abnormal gene from each parent and are unaffected at birth; but, with the introduction of feeding, a substance in the blood (phenylalanine and 10 breakdown products) builds up and causes brain damage, so that the untreated children become severely handicapped. Every baby in the UK has a blood test (sometimes called the heel test) for phenylalanine at about 6 days of age and if the diagnosis is confirmed a special diet is started.

Phytoremediation: Cleaning up waste or pollution using plants.

Placenta: The organ which links a developing foetus to the wall of the womb and the maternal blood supply.

Plasmid: A piece of parasitic genetic material found in a cell that can propagate itself using the cell’s energetic resources.

Polypeptide: An amino acid chain, one or more of which are needed to make up a protein.

Polygenes: The (hypothetical) many genes affecting a character, each having a small, additive effect on the character.

Polygenic: Controlled by or associated with more than one gene.

Polymer: A molecular chain, ring or web formed of units of smaller molecules, often repeating in an ordered fashion. 

Polymerase: An enzyme which links together the building blocks of a polymer to form the polymer.

Polymerase chain reaction (PCR): A laboratory process in which a specific DNA sequence is amplified many millions of times in only a few hours.

Polyploidy: Refers to the number of chromosomes in a cell. Most cells are normally diploid, i.e. have two sets of chromosomes. When the number is increased the cell shows polyploidy.

Positional cloning: Isolation of a gene through knowledge of its specific location on a particular chromosome.

Primer: See DNA primer.

Progeny: offspring

Prokaryote: The class of living things, including all bacteria, that do not have a nucleus in their cell.

Promoter: The region of a gene at which the RNA polymerase binds to start transcription. Most promoters are located upstream of the gene, except some eukaiyotic genes which have promoters internal to the gene.

Protein: A chemical substance made up of the elements carbon, nitrogen, oxygen and hydrogen which either makes up the structure of living tissues (eg muscle) or helps chemical reactions in living tissues to take place (eg enzymes). Egg-white is the purest example of a protein in everyday life. Made of one or more polypeptides. Enzymes and some hormones are proteins.

Proto-oncogenes Cellular genes which when mutated, or over-expressed become oncogenes.

Provirus: A virus that has inserted its genome or a complementaly copy of its genome into the host cell genome.



Recessive gene or allele: A gene that exercises little or no outward effect unless it is present in both of a pair of chromosomes, and therefore has been inherited from both parents, is said to be recessive.

Recombination: The formation of new combinations of alleles or new genes which occur when two homologous DNA or chromosomes break and exchange parts.

Recombinant DNA technology: The procedure for 'cutting' and 'splicing' DNA to make new combinations of genes.

Reductionism: The doctrine that complex systems can be completely understood in terms of its simplest parts. For example, an organism is to be completely understood in terms of its genes, a society in terms of its individuals, and so on.

Refuge: A stand of non-genetically modified crop in a GM crop designed to minimise the build up of pesticide resistance genes in the pest population by interbreeding of the two pest populations, i.e. exposed and unexposed to the pesticide concerned, thereby diluting the resistance genes.

Replication: The process whereby DNA makes copies of itself when a cell divides. The two strands of the DNA molecule unwind and each strand directs the synthesis of a new strand complementary to itself (and identical to its former partner)

Retinoblastoma: Eye cancer

Retrotransposon: A mobile genetic elements that depends on a reverse transcription step to move and to duplicate.

Reverse Transcription: The reverse of transcription - making a copy of complementaly DNA (eDNA) from an RNA sequence -catalyzed by the enzyme, reverse franscriptase.

Ribose: A constituent of RNA.

Ribosome: An organelle in the cell required for protein synthesis.

Ribosomal RNA: RNA molecules which make up the ribosome.

RNA: Ribonucleic acid. Forms of nucleic acid which are concerned with the synthesis of a protein. Messenger RNA is the means whereby the recipe for a polypeptide encoded in DNA which is contained in the nucleus of a cell, is transcribed and carried to the place in the cell where proteins are synthesised, namely the cytoplasm. The transcribed recipe then guides the assembly of the corresponding polypeptide, a process called translation.

RNA editing: The process in which the base sequence of the RNA transcript is changed by addition of bases to the RNA molecule or by chemical transformation of one base to another. This subverts the genetic information canied in the genes.

RNA polymerase: An enzyme that makes RNA.


Sex chromosomes: The X and Y chromosomes in human beings that determine the sex of an individual. Females have two X chromosomes in most body cells; males have an X and a Y chromosome.

Sickle cell disease: A single gene disorder caused by an altered polypeptide in the globin of haemoglobin. It was the first disorder in which a mutation in a structural gene was shown to produce an altered amino acid sequence. Inheritance is autosomal recessive. In homozygotes there is severe chronic anaemia, episodes of painful infarction (tissue death due to obstruction of the blood supply) especially of lungs, spleen and bones, and proneness to infection. It is connected with a resistance to malaria.

Somatic: Used to describe body tissues which do not include the sex cells (sperm & ova and their precursors)

Somaclonal variation Genetic variations of plant cells arising in cell culture, due to enhanced genetic instability.

Species: smallest unit of classification of living organisms commonly used; the group whose members have greatest mutual resemblance; a group of individuals able to breed amongst themselves but -- disregarding geographical constraints -- generally not with organisms of other groups. A reproductively isolated group whose genes do not usually combine with outsiders.

Species barrier: A hypothetical boundary believed to exist between one species and another (not a scientific concept!).

Stem cell: A cell that throughout life is able to produce all the cells within an organ. A change whether accidental or engineered, in the genetic complement of a stem cell will be passed to its progeny, by mitosis, and may be expressed in them. Appropriate stem cells are therefore an obvious target for somatic cell gene therapy.

Substantial equivalence: A non-scientific term to describe novel food crops produced by biotechnology which have passed all compulsory tests for stability, nutritional properties and safety.

Substrate: A chemical substance that takes part in a chemical reaction catalyzed by an enzyme.

Superweeds: Weeds that are tolerant to one or more herbicides.

Sustainable agriculture: Agriculture which minimises inputs in the form of fuel and chemicals (pesticides, pertilisers) and outputs in the form of air, groundwater and soil pollutants whilst producing soils that retain fertility for future generations (e.g. biodynamic, organic and permaculture systems).


Telos: That which makes a thing (organism) what it is.

Terminator technology: A biotechnological 'technology protection system' that renders sterile the seeds which are saved the first generation after the first sowing.

Terminator genes: Genes exploited in terminator technology.  

Thalassaemias: A group of disorders in which there is reduced production of one or more of the globin chains which constitute normal haemoglobin. This imbalance of globin chains results in chronic anaemia, which is a common cause of premature death and much suffering. Inheritance of each of the many genes which may be responsible is recessive.

Tissue: A collection of cells specialised to perform a particular function. Tissues are usually composed of several cell types. Organs, eg. heart, are made up of such tissues.

Toxicity: Poisonousness.

Toxin: A poisonous substance.

tPA: (tissue-type plasminogen activator) A protein in the blood which has an enzyme like function in helping the enzyme plasminogen to dissolve blood clots.

Trait: A character difference associated with a particular gene.

Transcription: The process of making a complementary sequence of the gene sequence in the genome, which is either used directly, as in case of Ribosomal RNAs (rRNAs) and Transfer RNAs (tRNAs), or is further processed into the messenger RNA, which is translated into protein. The process is catalyzed by the enzyme known as DNA-dependent RNA polymerase.

Transcription factors: Proteins in eukaryotes that regulate the transcription of other genes by binding to regulatory sequences of the gene, interaction with one another and with the RNA polymerase.

Transduction: In genetics. the transfer of genes by viruses from one organism to an-other.

Transfer RNA: RNA molecules which transfer specific amino acids to the messenger RNA so that the polypeptide it encodes can be synthesized.

Transformation In genetics, the transfer of genes by one organism taking up DNA belonging to another organism of the same or different species.

Transgenic: Describes an organism which has had DNA (genes) foreign to that organism put in it by genetic engineering (Transgenesis) in the laboratory. Related words: transgene, transgenesis.

Translation: The step in protein synthesis in which the messengerRNA directs the synthesis of a polypeptide of a particular amino-acid sequence by ‘decoding’ the genetic code.

Translocation: A rearrangement of chromosomal material between different chromosomes, not of the same pair.

Trisomy: The existence of three chromosomes instead of the normal two. e.g. trisomy 21 involves three copies of human chromosome 21.

Transposon - See Mobile genetic element.


Umbilicus: Organ connecting foetus to placenta.


Virus: A tiny infectious parasitic organism, too small to reproduce outside a host cell. Viruses carry either DNA or RNA, surrounded by a protein coat. Some cause disease, eg. chicken pox, influenza. Some viruses, however, suitably modified, can be used in research as a means of delivering a gene into cells. Here it is their ability to infect cells which is exploited. Its genetic material can become integrated into the cell’s genome to form provirus.

Virus vector: A virus used as a carrier for a gene when making a GMO.

Virulence Ability (of pathogens) to infect organisms and cause disease.

Vector: Carrier



X-linked: Describes the form of inheritance of diseases for which the gene responsible is carried on the X chromosome.

Xenotransplantation: animal to human organ transplants or xenografts. Their association with gene technology is because the animals will have to be genetically modified so that their organs when removed will 'look' sufficiently like human organs to the recipient's immune system that they will not be rejected.



Zygote: A fertilised ovum.


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See also glossaries at: http://www.genome.gov/glossary.cfm and FAO AgBiotech Glossary

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