recombinaseA class of enzymes that are able to alter the arrangement of DNA sequences in a site-specific way.
RecombinationThe production of a DNA molecule with segments derived from more than one parent DNA molecule.
recombination fractionThe proportion of recombinant (with respect to two loci) gametes arising from meiosis.
Recombination frequencyThe frequency at which crossing over occurs between two chromosomal loci--the probability that two loci will become unlinked during meiosis.
recombinational hot spotA chromosomal region where recombination appears to occur more frequently than expected.
reconstructed cellA viable transformed cell resulting from genetic engineering.
Red Blood CellsCells that carry oxygen throughout the body (also called erythrocytes).
reduction divisionThe first division of meiosis in which the chromosome number is reduced from the somatic to the gametic number.
refugium(pl.: refugia) An area set aside to provide protection/escape from ecological consequences occurring elsewhere.
regenerationIn biology, regrowth of damaged or destroyed tissue or body part.
Regenerative medicineMedical interventions that aim to repair damaged organs, most often by using stem cells to replace cells and tissues damaged by aging and by disease.
regulatorSubstance regulating growth and development of cells, organs, etc.
Regulatory geneA gene whose protein controls the activity of other genes or metabolic pathways.
regulatory sequenceA DNA sequence involved in regulating the expression of a gene, e.g. a promoter or operator region (in the DNA molecule).
rejuvenation1. Reversion from adult to juvenile stage. 2. The process of regular reproduction of seed stocks or collections in gene banks, in order to ensure…
Relaxed plasmidA plasmid that replicates independently of the main bacterial chromosome and is present in 10-500 copies per cell. (See Plasmid.)
release factor1. A soluble protein that recognizes termination codon s in mRNA s and terminates translation in response to these codons. 2.
RemediationThe cleanup or containment of a hazardous waste disposal site to the satisfaction of the applicable regulatory agency.
renaturationOf DNA, the reforming of two complementary molecules into a double-stranded structure, following heat or chemical induction of dissociation (denaturation).
RenatureThe reannealing (hydrogen bonding) of single- stranded DNA and/or RNA to form a duplex molecule.
renninAn enzyme, secreted by cells lining the stomach in mammals, responsible for the clotting of milk. Used in the manufacture of certain dairy products.
repeat unitA sequence of nucleotide s that occurs repeatedly, often in a head-to-tail arrangement (tandemly).
Repetitive DNADNA sequences that are present in a genome in many copies, some of it originating from retrotransposon activity.
replacementThe addition of a cloned corrected copy of a defective gene. See: homogenotization.
replacement therapyThe administration of metabolites, co-factors or hormones that are deficient as the result of a genetic disease.
replica platingDuplicating a population of bacterial colonies growing on agar medium in one Petri plate to agar medium in another Petri plate.
replicaseA viral enzyme necessary for the replication of the virus in the host cell.
ReplicationThe in vivo synthesis of double-stranded DNA by copying from a single-stranded template.
replication forkY shaped structure associated with DNA replication. It represents the point at which the strands of double-stranded DNA are separated so that replication…
replicative form(Abbreviation: RF). The molecular configuration of viral nucleic acid that is the template for replication in the host cell.
RepliconA chromosomal region containing the DNA sequences necessary to initiate DNA replication processes.
replisomeThe complete replication apparatus, present at a replication fork, that carries out the replication of DNA.
Reporter geneA gene that encodes a product that can be readily assayed. Used as to confirm the incorporation of a transgene into, organ or tissue, and as a means of…
repressible enzymeAn enzyme whose activity can be diminished by the presence of a regulatory molecule.
repressible geneA gene whose expression can be diminished or extinguished by the presence of a regulatory molecule.
repressionInhibition of transcription by preventing RNA polymerase from binding to the transcription initiation site.
repressorA DNA-binding protein in prokaryotes that blocks gene transcription by binding to the operator.
reproduction1. Sexual reproduction: the regular alteRNA tion of meiosis and fertilization which provides for the production of offspring.
Reproductive cloningSomatic cell nuclear transfer used for the production of a fetus and delivery of a live offspring that is genetically identical the donor of the somatic…
repulsionA double heterozygote in which the dominant (or wild-type) allele at one locus and the recessive (or mutant) allele at a second linked locus occur on the…
residue1. See: polymer. 2. Materials remaining after degradation and/or attempted removal, e.g. pesticide residues in food.
ResistanceThe ability of an organism to develop ways to be impervious to specific threats to their existence.
resistance factorA plasmid that confers antibiotic resistance to a bacterium.
Resistance managementStrategies that can delay the onset of resistance. For insect resistance management, this includes the use of a refuge in which the insect will not be…
rest periodA physiological condition of viable seed s, buds or bulbs that prevents growth even in the presence of otherwise favourable environmental conditions.
restitution nucleusA single nucleus arising from a failure of nuclear division, either during meiosis, in which a gamete is formed with the unreduced chromosome number; or…
restriction endonucleaseA class of enzymes that cut DNA after recognizing a specific sequence. The three types of restriction endonuclease are: I.
Restriction endonuclease (enzyme)A class of endonucleases that cleaves DNA after recognizing a specific sequence, such as BamH1 (GGATCC), EcoRI (GAATTC), and HindIII (AAGCTT). Type I.
restriction enzymesEnzymes that recognize a specific sequence of double-stranded DNA and cut the DNA at that site.
restriction exonucleaseA class of enzymes that degrade DNA or RNA, starting from either the 5'- or the 3'-end.
restriction fragmentA shortened DNA molecule generated by the cleavage of a larger molecule by one or more restriction endonucleases.
restriction fragment length polymorphism(Abbreviation: RFLP). A class of genetic marker based on the detection of variation in the length of restriction fragments generated when DNA is treated…
Restriction fragment length polymorphism (RFLP)Differences in nucleotide sequence between alleles at a chromosomal locus result in restriction fragments of varying lengths detected by Southern analysis.
Restriction-enzyme cutting siteA specific nucleotide sequence of DNA at which a particular restriction enzyme cuts the DNA. Some sites occur frequently in DNA (e.g.
Retinoic acid(REH-tih-NOH-ik A-sid) A form of vitamin A that is made by the body, and can also be made in the laboratory.
retro-elementAny of the integrated retrovirus es or the transposable elements that resemble them.
retroposonA transposable element that moves via reverse transcription but lacks the long terminal repeat sequences necessary for autonomous transposition.
Retroviral infectionThe presence of retroviral vectors, such as some viruses, which use their recombinant DNA to insert their genetic material into the chromosomes of the…
retroviral vectorsGene transfer systems based on viruses that have RNA as their genetic material.
retrovirus(REH-troh-VY-rus) A type of virus that has RNA instead of DNA as its genetic material.
reversal transferTransfer of a culture from a callus-supporting medium to a shoot-inducing medium.
Reverse geneticsUsing linkage analysis and polymorphic markers to isolate a disease gene in the absence of a known metabolic defect, then using the DNA sequence of the…
Reverse transcriptaseAn enzyme that uses an RNA molecule as a template for the synthesis of a complementary DNA strand. Synonym: RNA -dependent DNA polymerase.
reverse transcription(ree-VERS tran-SKRIP-shun) In biology, the process in cells by which an enzyme makes a copy of DNA from RNA.
reversionRestitution of a mutant gene to the wild-type condition, or at least to a form that gives the wild-type phenotype; more generally, the appearance of a…
rhizobacteriumA micro-organism whose natural habitat is near, on, or in, plant roots.
RhizobiaBacteria in a symbiotic relationship with leguminous plants that results in nitrogen fixation. See Nitrogen fixation.
Rhizobium(pl.: Rhizobia) Prokaryotic species which are able to establish a symbiotic relationship with leguminous plants, as a result of which elemental nitrogen…
RhizosphereThe soils region on and around plant roots.
Ri plasmidA class of large conjugative plasmid s found in the soil bacterium Agrobacterium rhizogenes , which can infect certain plants and cause hairy root disease.
ribonuclease(Abbreviation: RNA se). Any enzyme that catalyses the hydrolysis of RNA.
ribonucleic acid(RY-boh-noo-KLAY-ik A-sid) One of the two types of nucleic acids found in all cells.
Ribonucleic acid (RNA)A chemical similar to a single strand of DNA. In RNA, the letter U, which stands for uracil, is substituted for T in the genetic code.
RiboseA monosaccharide found in all ribonucleosides, ribonucleotides and RNA. Its close analogue, 2-deoxyribose, is similarly found in all deoxyribonucleosides…
ribosomal binding siteA sequence of nucleotides near the 5' end of a bacterial mRNA molecule that facilitates the binding of the mRNA to the small ribosomal sub-unit.
ribosomal DNAThe coding locus for ribosomal RNA. This is generally a large and complex locus, typically composed of a large number of repeat units, separated from one…
ribosomal RNA(Abbreviation: rRNA). The RNA molecules that are essential structural and functional components of ribosomes, where protein synthesis occurs.