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Home >>Biotechnology Dictionary >> DNA polymerase - Duplication
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DNA polymerase - an enzyme that catalyses the synthesis of double stranded DNA, using single-stranded DNA as a template.
DNA polymorphism - the existence of two or more alternative forms (alleles) of a chromosomal locus that differ in nucleotide sequence or have variable numbers of repeated nucleotide units.
Donor plant - an explant, graft or cutting used as a source of plant material for micro propagation purposes. a.k.a. ortet cf explant.
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DNA primase - an enzyme that catalyses the synthesis of short strands of RNA that initiate the synthesis of DNA strands.
DNA probe - a labelled (tagged) segment of DNA that is able, after a DNA, hybridisation reaction, to detect a specific DNA sequence in a mixture of sequences. If the tagged sequence is complementary to anyone in the mixture, the two sequences will form a double helix. This will be identified thanks to its label (either by radioactivity or fluorescence).
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DNA repair - a variety of mechanisms that repair errors that occur during DNA replication.
DNA repair enzymes - enzymes that catalyse the repair of DNA.DNA replication the process whereby DNA makes exact copies itself, under the action of and control of DNA polymerase.
Domestic animal diversity - in AnGR The spectrum of genetic differences within each breed, and across all breeds within each domestic animal species, together with the species differences; all of which are available for the sustainable intensification of food and agriculture production.
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DNA sequencing - procedures for determining the nucleotide sequence of a DNA fragment There are two common methods for doing this:
1. the Maxam and Gilbert technique (chemical degradation), that uses different chemicals to break the DNA into fragments at specific bases; or
2. the Sanger technique (called the di-deoxy or chainterminating method) uses DNA polymerase to make new DNA chains, with di-deoxy nucleotides (chain terminators) to stop the chain randomly as it grows. In both cases, the DNA fragments are separated according to length by polyacrylamide gel electrophoresis, enabling. the sequence to be read Directly from the gel.
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DNA topoisomerase - an enzyme that catalyses the introduction or removal of supercoils in DNA.
DNase an enzyme that catalyses the cleavage of DNA. DNase I is a digestive enzyme secreted by the pancreas, that degrades DNA into shorter nucleotide fragments. Many other endonucleases and exonucleases are involved in DNA repair and replication. cf nuclease.
Domain - a segment of a protein that has a discrete function or conformation. At the protein level, a domain can be as small as a few amino acid residues or as large as half of the entire protein.
Dominance - the type of gene action exhibited by a dominant allele (g. v.).
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Dolly - the [name of the] first mammal to be created by cloning a cell from an adult animal. In this particular case, the cell came from the mammary tissue of an adult ewe. The creation of Dolly showed that the process of differentiation into adult tissue is not, as previously thought, irreversible. The result was achieved by nuclear transfer (q.v.). Dolly's birth was announced in 1997. Since then, cattle and mice have also been cloned from adult cells.
Dominant - 1.describing an allele whose effect with respect to a particular trait is the same in heterozygotes as in homozygotes. The opposite is recessive.
2. describing the most conspicuously abundant and characteristic species of a community.
3. describing an animal that is allowed priority in access to food, mates, etc., by others of its species because of its success in previous aggressive. encounters.
Dominant marker selection - selection of cells via a gene encoding a product that enables only the cells that carry the gene to grow under particular conditions. For example, plant and animal cells that express the introduced Neor gene are resistant to the compound G418, while cells that do not carry the Neor gene are killed by G418. a.k.a. positive selection.
Dominant selectable marker gene - a gene that allows the host cell to survive under conditions where it would otherwise die.
Dominant(-acting) oncogene - a gene that stimulates cell proliferation and contributes to oncogenesis when present in a single copy. See oncogene.
Dormancy - an inactive period in the life of an animal or plant during which growth slows or completely ceases. Physiological changes associated with dormancy help the organism survive adverse environmental conditions. Annual plants survive the winter as dormant seeds, while many perennial plants survive as dormant tubers, rhizomes, or bulbs. Hibernation and aestivation in animals help them survive extremes of cold and heat respectively. cf rest period.
Dosage compensation - a phenomenon whereby inactivation of all but one of the X chromosomes in female mammals results in males and females producing the same quantity of peptide from X linked genes.
Double crossing over - two simultaneous reciprocal breakage and reunion events between the same two chromatids.
Double fertilisation - a process, unique to flowering plants, in which two male nuclei, which have travelled down the pollen tube, separately fuse with different female nuclei in the embryo sac. The first male nucleus fuses with the egg cell to form the zygote; the second male nucleus fuses with the two polar nuclei to form a triploid nucleus that develops into the endosperm.
Double helix - describes the coiling of the antiparallel strands of the DNA molecule, resembling a spiral staircase in which the paired bases form the steps and the sugar-phosphate backbones form the rails.
Double recessive - an organism homozygous for a recessive allele at each of two loci.
Double-stranded complementary DNA) - a double-strand DNA molecule created from a cDNA template.
Downstream - 1. in molecular biology, the, stretch of nucleotides of DNA that lie in the 3' direction from the site of initiation of transcription, which is designated as +1 (remembering the convention that the sequence of a DNA molecule is written from the 5' end to the 3' end). Downstream nucleotides are marked with plus signs, e.g., +2, +10. Also, to the 3' side of a particular gene or sequence of nucleotides.
2. in chemical engineering those phases of a manufacturing process that follow the biotransformation stage. Usually refers to the recovery and. purification of the product of a fermentation process.
Downstream processing - a general term for all the things which happen in a biotechnological process after the biology, be it fermentation of a microorganism or growth of a plant. It is particularly relevant to fermentation processes, which produce a large quantity of a dilute mixture of substances, products and micro-organisms. These must be separated, and the product must be concentrated and purified, and converted into a form which is useful.
Drug delivery - method by which a therapeutic agent is delivered to its site of action. For traditional therapeutic agents this is another name for formulation. However, biotechnology has allowed the development of a range of new therapeutic agent delivery systems, such as liposomes and other encapsulation techniques, and a range of mechanisms that target a therapeutic agent to a particular cell or tissue. See therapeutic agent.
Dry weight- the moisture-free weight of tissue obtained by drying at high (oven-drying) or low (freeze-drying) temperatures for an interval sufficient to remove all water.
Dual culture- a culture made of a plant tissue and one organism (such as a nematode) or an obligate parasite/ micro-organism (such as a fungus). Dual culture techniques are used for a variety of purposes, including assessing host-parasite interactions and the production of axenic cultures.
Duplex DNA - double-stranded DNA.
Duplication - the occurrence of a segment more than once in the same chromosome or enome.
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