Glossary of Genetic Engineering Terms

By Dr. Mae-Wan Ho


Adaptive mutation, or Directed mutation The phenomenon whereby bacteria and yeast cells in stationary (non-growing) phase, have some way of producing (or selectively retaining) only the most appropriate mutations that enable them to make use of new substrates for growth.

Allele A particular variant of a gene.

Allergen A substance that causes the body to react hypersensitively to it.

Antibiotic resistance marker genes Genes coding for antibiotic resistance used in genetic modification. They allow the cells that have taken up the foreign GM construct to be selected with antibiotics, and frequently remain in the genetically modified organism and transgenic line created.

Autosome A chromosome other than the sex-chromosome, or sex-deter-mining chromosome.

Bacteriophage Any virus that infect bacteria, also known as phage.

Biofilm A layer of extracellular matrix containing quiescent, non-proliferating micro-organisms.

Cell line A supposedly genetically uniform population of cells derived from one individual cell. The genetic identity of all the cells is a fiction, as the genetic material is subject to many ‘fluid genome’ processes that constantly make cells genetically different from one another, and especially in culture. Both plant and animal cells are subject to large variations known collectively as somaclonal variations.

Chromosome A structural unit of genetic material consisting of a long molecule of DNA complexed with special proteins in eukaryotes, but not in prokaryotes

Clone An identical copy of an individual organism, a cell, or a gene, or the totality of all the identical copies made from an individual organism, a cell, or a gene. In genetics, the clone implies identical in genetic make-up to the original.

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

Directed mutation See Adaptive mutation.

DNA DeoxyriboNucleic Acid, the genetic material consisting of a long chain of individual units called nucleotides, each consisting of a base joined to a sugar and a phosphate group.

DNAse Deoxyribonuclease, an enzyme that breaks down DNA.

DNA sequence The sequence of bases in a stretch of DNA. There are 4 different bases, which are simply represented by the alphabets, A, T, C and G. An example of a DNA sequence is as follows: ATTTCCGCTACGCGTTA... An RNA sequence is similar, except that the alphabet T is replaced by U.

DNA methylation An endogenous process in the cell which adds a methyl group, -CH3, to the base cytosine or adenosine, resulting in gene-silencing, or failure of the gene to become expressed.

DNA polymerase An enzyme that makes DNA.

Dominant allele An allele which is expressed when only one copy is present in an individual, i.e., in heterozygous condition.

Ecosystem The totality of all plant and animal species that constitute an interdepent, interrelated community.

Entropy A measure of the disordered, degraded energy that is unavailable for work.

Enzyme A Protein produced by living organisms that acts as a catalyst for a specific biochemical (metabolic) reaction.

Epistasis Interaction between genes.

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.

Gene A unit of heredity, usually a stretch of genetic material (DNA or RNA) with a defined function in the organism or cell, such as one for a protein. There are many genes within a genome. For example, the human genome is now found to contain about 30 000 genes, while the rice genome has about 50 000.

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, isolating the gene and identifying it.

Gene expression The synthesis of the gene-product or protein encoded by the gene.

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

Gene therapy Treating diseases by replacing the defective gene, either by incorporating a normal copy of the gene in the germ-cells (egg or sperm) or in the embryo (germline gene replacement therapy), or by supplying copies of the normal gene to be taken up and incorporated into cells of the adult (somatic cell gene replacement therapy).

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 marker 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.

Genetic modification or transgenesis is the process whereby a genetically modified organism is made in the laboratory. This involves making artificial or modified genetic material (GM constructs) which are inserted into the genomes of cells or embryos. The cell or embryo is regenerated to an organism, out of which a GM line or transgenic line is derived.

Genetically modified organism (GMO) An organism which has foreign DNA inserted into its genome by means of genetic modification in the laboratory.

Genome The totality of all the genetic material (deoxyribonucleic acid or DNA) in an organism, organised in a precise, though by no means fixed or constant way. In the case of viruses, most of them will have ribonucleic acid or RNA as the genetic material.

Genotype The precise variant(s) of the gene(s) carried by an individual.

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

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

Horizontal gene transfer The direct uptake of foreign genetic material by cells and incorporation into the cells’ genome.

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.

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 An organism that can be seen only under a microscope, usually, an ordinary light microscope. It includes bacteria, mycoplasm, yeasts, single-celled algae and protozoa. Multicellular organisms are normally not included, nor fungi apart from yeasts. Viruses are also not automatically included, as many scientists do not classify them as organisms.

Mitochondria Membrane-bound cellular organelles in which organic substrates derived from food are oxidized to provide energy for all kinds of vital activities. 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.

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.

Multigene families are 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.

Nuclear transplant cloning A process whereby the nucleus containing the genome of an adult cell is transferred into an egg from which the nucleus was previously removed. The egg with the transplant nucleus is then stimulated to divide and develop into an organism.

Nucleus 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.

Operon A multigenic unit consisting of a regulator gene, a promoter-operator region and one or more other genes whose expression is regulated.

Pathogen Any agent that can cause disease.

Phage A bacterial virus

Phenotype The expressed characteristics, or an expressed character of an organism due to its genotype.

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

Polypeptide or Protein A long chain of different amino-acids joined together by special chemical (peptide) bonds.

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

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

Promoter A piece of genetic material that acts as a gene switch, so that a gene can become expressed in the cell. It is the region at which the RNA polymerase binds to start transcription. Most promoters are located upstream of the gene, except that some eukaryotic genes have promoters internal to the gene.

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

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

Recessive allele An allele which is not expressed unless two copies are present in the individual, i.e., in homozygous condition.

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

Recombination hotspot A frequent breakpoint in the DNA or RNA, which promotes recombination.

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.

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 complementary DNA (cDNA) from an RNA sequence - catalyzed by the enzyme, reverse transcriptase.

Ribosome An organelle in the cell required for protein synthesis.

Ribosomal RNA RNA molecules which make up the ribosome.

RNA RiboNucleic Acid, similar to DNA except for the sugar in the nucleotide unit, which is ribose, instead of deoxyribose, and the base Uracil instead of Thymine. RNA is the genetic material for RNA viruses,

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 transform-ation of one base to another. This subverts the genetic information carried in the genes.

RNA polymerase An enzyme that makes RNA.

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

Stem cells Cells that have the potential to multiply indefinitely and become many different cell types.

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

Thermodynamics The branch of physics dealing with the transformation of energy, especially of heat and other forms of energy.

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 another.

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 organism An organism created by genetic engineering, in which one or more foreign genes have been incorporated into its genome.

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.

Transposon See Mobile genetic element.

Vector A carrier or transmitter, of genes or of disease. Artificial vectors are made in genetic engineering for multiplying and transferring genes into genomes.

Virus A parasitic genetic element enclosed in a protein coat that can replicate in cells, and form infectious particles, or remain dormant in the cells. Its genetic material can become integrated into the cell's genome to form provirus.

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