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U The uracil residue in RNA.
ultrasonication See sonication.
ultraviolet light; ultraviolet radiation (UV) The portion of the electromagnetic spectrum with wavelengths from about 100 to 400 nm; between ionizing radiation (X-rays) and visible light. UV is absorbed by DNA and is highly mutagenic to unicellular organisms and to the epidermal cells of multicellular organisms. UV light is used in tissue culture for its mutagenic and bactericidal properties.
undefined A medium or substance added to medium in which not all of the constituents or their concentrations are chemically defined, such as media containing coconut milk, malt extract, casein hydrolysate, fish emulsion or other complex compounds. cf organic complex.
understock Host plant for a grafted scion, a branch or shoot from another plant; an understock may be a fully grown tree or a stump with a living root system.
undifferentiated In a meristematic state or resembling a meristem; lacking the specialized or differential gene expression characteristic of specialized cells.
unequal crossing over Crossing over between repeated DNA sequences that have paired out of register, creating duplicated and deficient products.
unicellular Describing tissues, organs or organisms consisting of a single cell.
unisexual Describing animals and plants possessing either male or female reproductive organs, but not both.
univalent An unpaired chromosome at meiosis.
universal donor cells Cells that, after introduction into a recipient, will not induce an immune response that leads to their rejection.
universality Referring to the genetic code, the codons have the same meaning, with minor exceptions, in virtually all species.
unorganized growth In vitro formation of tissues with few differentiated cell types and no recognizable structure; many call are unorganized. cf organized growth.
upstream processing See upstream (2).
upstream 1. In molecular biology, the stretch of DNA base pairs that lie in the 5´ direction from the site of initiation of transcription. Usually the first transcribed base is designated +1 and the upstream nucleotides are marked with minus signs, e.g., -1, -10. Also, to the 5´ side of a particular gene or sequence of nucleotides.
2. In chemical engineering, those phases of a manufacturing process that precede the biotransformation step. Refers to the preparation of raw materials for a fermentation process. Also called upstream processing.
uracil A pyrimidine base found in RNA but not in DNA. In DNA, uracil is replaced by thymine.
utilization of farm animal genetic resources In AnGR: The use and development of animal genetic resources for the production of food and agriculture. (Source: FAO, 1999)
The use in production systems of AnGRs that already possess high levels of adaptive fitness to the environments concerned, and the deployment of sound genetic principles, will facilitate sustainable development of the AnGRs and the sustainable intensification of the production systems themselves. The wise use of AnGRs is possible without depleting domestic animal diversity. Development of AnGRs includes a broad mix of ongoing activities that must be well planned and executed for success, and compounded over time, hence with high value. It requires careful definition of breeding objectives, and the planning, establishment and maintenance of effective and efficient animal recording and breeding strategies. (Source: FAO, 1999)
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