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| Recessive gene |
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Characterized as having a phenotype expressed only when both copies of the gene are mutated or missing.
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| Recessive(-acting) oncoge |
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A single copy of this gene is sufficient to suppress cell proliferation; the loss of both copies of the gene contributes to cancer formation. (See Oncogene.)
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| Recognition sequence (sit |
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A nucleotide sequence--composed typically of 4, 6, or 8 nucleotides--that is recognized by a restriction endonuclease. Type II enzyrnes cut (and their corresponding modification enzymes methylate) within or very near the recognition sequence.
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| Recombinant |
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A cell that results from recombination of genes.
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| Recombinant DNA |
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The process of cutting and recombining DNA fragments from different sources as a means to isolate genes or to alter their structure and function.
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| Recombination frequency |
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The frequency at which crossing over occurs between two chromosomal loci--the probability that two loci will become unlinked during meiosis.
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| Regulatory gene |
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A gene whose protein controls the activity of other genes or metabolic pathways.
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| Relaxed circle plasmid |
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See Plasmid.
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| Relaxed plasmid |
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A plasmid that replicates independently of the main bacterial chromosome and is present in 10-500 copies per cell. (See Plasmid.)
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| Renature |
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The reannealing (hydrogen bonding) of single- stranded DNA and/or RNA to form a duplex molecule.
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| Replicon |
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A chromosomal region containing the DNA sequences necessary to initiate DNA replication processes.
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| Repressor |
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A DNA-binding protein in prokaryotes that blocks gene transcription by binding to the operator.
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| Restriction endonuclease |
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A class of endonucleases that cleaves DNA after recognizing a specific sequence, such as BamH1 (GGATCC), EcoRI (GAATTC), and HindIII (AAGCTT). Type I. Cuts nonspecifically a distance greater than 1000 bp from its recognition sequence and contains both restriction and methylation activities. Type II. Cuts at or near a short, and often symmetrical, recognition sequence. A separate enzyme methylates the same recognition sequence. Type III. Cuts 24-26 bp downstream from a short, asymmetrical recognition sequence. Requires ATP and contains both restriction and methylation activities.
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| Restriction map |
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See Mapping.
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| Restriction-fragment-leng |
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Differences in nucleotide sequence between alleles at a chromosomal locus result in restriction fragments of varying lengths detected by Southern analysis.
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| Retrovirus |
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A member of a class of RNA viruses that utilizes the enzyme reverse transcriptase to reverse copy its genome into a DNA intermediate, which integrates into the hostcell chromosome. Many naturally occurring cancers of vertebrate animals are caused by retroviruses.
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| Reverse genetics |
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Using 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 cloned gene to predict the amino acid sequence of its encoded protein.
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| Reverse transcriptase (RN |
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An enzyme isolated from retrovirus-infected cells that synthesizes a complementary (c)DNA strand from an RNA template.
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| RFLP |
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See Restriction-fragment-length polymorphism.
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| Rhizobia |
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Bacteria in a symbiotic relationship with leguminous plants that results in nitrogen fixation. See Nitrogen fixation.
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| Rhizosphere |
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The soils region on and around plant roots.
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| Ribosomal RNA (rRNA). |
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The RNA component of the ribosome. (See RNA.)
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| Ribosome |
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Cellular organelle that is the site of protein synthesis during translation. See Organelle, Translation.
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| Ribosome-binding site |
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The region of an mRNA molecule that binds the ribosome to initiate translation.
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| Ribozyme |
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See Catalytic RNA.
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| RNA (ribonucleic acid). |
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An organic acid composed of re- peating nucleotide units of adenine, guanine, cytosine, and uracil, whose ribose components are linked by phosphodiester bonds. (See Antisense RNA, Heterogeneous nuclear RNA, Messenger RNA, Ribosomal RNA, RNA polymerase, Small nuclear RNA, Transfer RNA.)
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| RNA polymerase |
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Transcribes RNA from a DNA template. (See Polymerase, RNA.)
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| S&E |
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See U.S. Department of Agriculture.
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| Salmonella |
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A genus of rod-shaped, gram-negative bacteria that are a common cause of food poisoning.
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| Satellite RNA (viroids) |
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A small, self-splicing RNA molecule that accompanies several plant viruses, including tobacco ringspot virus.
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| Selectable marker |
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A gene whose expression allows one to identify cells that have been transforrned or transfected with a vector containing the marker gene. (See B-Lactamase, Kanr.)
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| Self-pollination |
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Pollen of one plant is transferred to the female part of the same plant or another plant with the same genetic makeup.
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| Semiconservative replicat |
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During DNA duplication, each strand of a parent DNA molecule is a template for the synthesis of its new complementary strand. Thus, one half of a preexisting DNA molecule is conserved during each round of replication.
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| Sequence hypothesis |
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Francis Crick's seminal concept that genetic information exists as a linear DNA code; DNA and protein sequence are colinear.
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| Sequence-tagged site (STS |
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A unique (single-copy) DNA sequence used as a mapping landmark on a chromosome.
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| Sexual reproduction |
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The process where two cells (gametes) fuse to form one hybrid, fertilized cell. See Asexual reproduction, Gamete, Hybrid.
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| Signal transduction |
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The biochemical events that conduct the signal of a hormone or growth factor from the cell exterior, through the cell membrane, and into the cytoplasm. This involves a number of molecules, including receptors, pro- teins, and messengers.
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| Site-directed mutagenesis |
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The process of introducing spe- cific base-pair mutations into a gene.
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| Small nuclear RNA (snRNA) |
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Short RNA transcripts of 100-300 bp that associate with proteins to form small nuclear ribonucleoprotein particles (snRNPs), which participate in RNA processing. (See RNA.)
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| snRNA |
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See Small nuclear RNA.
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| Somatic cell |
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Any nongerm cell that composes the body of an organism and which possesses a set of multiploid chromosomes (diploid in most organisms). (See Gamete, Somatic cell gene therapy.)
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| Somatic cell gene therapy |
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The repair or replacement of a defective gene within somatic tissue. (See Somatic cell.)
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| Somatotrophin |
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See Human growth hormone.
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| Southern blotting |
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See Southern hybridization.
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| Southern hybridization (S |
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A procedure in which DNA restriction fragments are transferred from an agarose gel to a nitrocellulose filter, where the denatured DNA is then hybridized to a radioactive probe (blotting). (See Hybridization.)
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| Species |
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A classification of related organisms that can freely interbreed.
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| Spore |
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A form taken by certain microbes that enables them to exist in a dormant stage. It is an asexual reproductive cell. See Asexual reproduction, Dormant.
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| Stationary phase |
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The plateau of the growth curve after log growth, during which cell number remains constant. New cells are produced at the same rate as older cells die. (See Growth phase.)
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| Sticky end |
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A protruding, single-stranded nucleotide se- quence produced when a restriction endonuclease cleaves off center in its recognition sequence.
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