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| Persistence |
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Ability of an organism to remain in a particular setting for a period of time after it is introduced.
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| Pesticide |
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A substance that kills harmful organisms (for example, an insecticide or fungicide).
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| Phage (particle) |
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See Bacteriophage.
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| Phenotype |
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The observable characteristics of an organism, the expression of gene alleles (genotype) as an observable physical or biochemical trait. See Genotype.
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| Pheromone |
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A hormone-like substance that is secreted into the environment.
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| Phosphatase |
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An enzyme that hydrolyzes esters of phosphoric acid, removing a phosphate group.
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| Phosphodiester bond |
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A bond in which a phosphate group joins adjacent carbons through ester linkages. A condensation reaction between adjacent nucleotides results in a phosphodiester bond between 3' and 5' carbons in DNA and RNA.
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| Phospholipid |
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A class of lipid molecules in which a phos- phate group is linked to glycerol and two fatty acyl groups. A chief component of biological membranes. (See Inositol phospholipid.)
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| Phosphorylation |
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The addition of a phosphate group to a compound.
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| Physical map |
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A map showing physical locations on a DNA molecule, such as restriction sites, and sequence-tagged sites. (See Mapping.)
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| Plant Pest Act (PPA) |
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See U.S. Department of Agriculture.
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| Plant Variety Act (PVA) |
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See U.S. Department of Agriculture.
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| Plaque |
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A clear spot on a lawn of bacteria or cultured cells where cells have been Iysed by viral infection.
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| Plasmid (p). |
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A circular DNA molecule, capable of autonomous replication, which typically carries one or more genes encoding antibiotic resistance proteins. Plasmids can transfer genes between bacteria and are important tools of transformation for genetic engineers. (See Nicked circle, pAMP, Relaxed plasmid, Stringent plasmid, Supercoiled plasmid.)
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| Pleiotrophy |
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The effect of a particular gene on several different traits.
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| Point mutation |
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A change in a single base pair of a DNA sequence in a gene. (See Mutation.)
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| Poly(A) polymerase |
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Catalyzes the addition of adenine residues to the 3' end of pre-mRNAs to form the poly(A) tail. (See Polymerase.)
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| Polyacrylamide gel electr |
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Electrophoresis through a matrix composed of a synthetic polymer, used to separate proteins, small DNA, or RNA molecules of up to 1000 nucleotides. Used in DNA sequencing. (See Electrophoresis.)
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| Polyclonal antibodies |
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A mixture of immunoglobulin molecules secreted against a specific antigen, each recognizing a different epitope.
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| Polygenic |
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Controlled by or associated with more than one gene.
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| Polylinker |
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A short DNA sequence containing several re- striction enzyme recognition sites that is contained in cloning vectors.
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| Polymer |
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A molecule composed of repeated subunits.
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| Polymerase (DNA). |
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Synthesizes a double-stranded DNA molecule using a primer and DNA as a template. (See Poly(A) polymerase, Polymerase chain reaction, RNA polymerase, Taq polymerase.)
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| polymerase chain reaction |
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A procedure that en- zymatically amplifies a DNA polymerase. (See Polymerase.)
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| Polymorphisms |
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Variant forms of a particular gene that occur simultaneously in a population.
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| Polynucleotide |
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A DNA polymer composed of multiple nucleotides. (See Nucleotide.)
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| Polypeptide (protein) |
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A polymer composed of multiple amino acid units linked by peptide bonds.
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| Polyploid |
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A multiple of the haploid chromosome number that results from chromosome replication without nuclear division.
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| Polysaccharide |
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A polymer composed of multiple units of monosaccharide (simple sugar).
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| Polyvalent vaccine |
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A recombinant organism into which has been cloned antigenic determinants from a number of different disease-causing organisms. (See Vaccine.)
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| Population |
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A local group of organisms belonging to the same species and capable of interbreeding.
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| PPA |
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See U.S. Department of Agriculture.
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| Primary cell |
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A cell or cell line taken directly from a living organism, which is not immortalized.
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| Primer |
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A short DNA or RNA fragment annealed to single-stranded DNA, from which DNA polymerase extends a new DNA strand to produce a duplex molecule.
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| Prion |
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See Proteinaceous infectious particle.
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| Probe |
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A sequence of DNA or RNA, labeled or marked with a radioactive isotope, used to detect the presence of complementary nucleotide sequences. See Nucleotide.
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| Prokaryote |
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A bacterial cell lacking a true nucleus; its DNA is usually in one long strand. See Eukaryote.
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| Promoter |
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A region of DNA extending 150-300 bp upstream from the transcription start site that contains binding sites for RNA polymerase and a number of proteins that regulate the rate of transcription of the adjacent gene. (See Constitutive promoter.)
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| Pronucleus |
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Either of the two haploid gamete nuclei just prior to their fusion in the fertilized ovum.
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| Protease |
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An enzyme that cleaves peptide bonds that link amino acids in protein molecules.
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| Protein |
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A polymer of amino acids linked via peptide bonds and which may be composed of two or more polypeptide chains. (See Polypeptide.)
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| Protein kinase |
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An enzyme that adds phosphate groups to a protein molecule at serine, threonine, or tyrosine residues.
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| Proteinaceous infectious |
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A proposed pathogen composed only of protein with no detectable nucleic acid and which is responsible for Creutzfeldt-Jakob disease and kuru in humans and scrapie in sheep.
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| Proteolytic |
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The ability to break down protein molecules.
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| Proto-oncogene |
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See oncogene.
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| Public Health Service Act |
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See Food and Drug Administration.
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| pUC |
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A widely used expression plasmid containing a -galactosidase gene. (See Plasmid.)
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| PVA |
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The Plant Variety Act. See U.S. Department of Agriculture.
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| Reading frame |
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A series of triplet codons beginning from a specific nucleotide. Depending on where one begins, each DNA strand contains three different reading frames. (See Open reading frame, Overlapping reading frames.)
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