positional candidate geneA gene known to be located in the same region as a DNA marker that has been shown to be linked to a single-locus trait or to a QTL, and whose deduced…
positional cloningA strategy for gene cloning that relies on the identification of closely linked markers to the target trait, and then uses chromosome walking to identify…
positive control systemA mechanism in which a regulatory protein (s) is required to turn on gene expression.
positive selectionA method by which cells that carry a DNA insert integrated at a specific chromosomal location can be selected, since this integration confers a…
Post-implantation embryoImplanted embryos in the early stages of development until the establishment of the body plan of a developed organism with identifiable tissues and organs.
pre-transplantA stage in micropropagation - the rooting and hardening process prior to transfer to soil.
precautionary principleThe approach whereby any possible risk associated with the introduction of a new technology is avoided, until a full understanding of its impact on…
precocious germinationEarly germination of a seed or embryo, prior to the full maturation of the embryo.
Precursor CellsIn fetal or adult tissues, these are partly differentiated cells that divide and give rise to differentiated cells. Also known as progenitor cells.
PreimplantationWith regard to an embryo, preimplantation means that the embryo has not yet implanted in the wall of the uterus.
pressure potentialThe pressure generated within a cell, being the net difference between the cell's osmotic potential and the water potential of the external environment.
preventive immunizationInfection with an antigen to elicit an antibody response that will protect the organism against future infections. Synonym: vaccination.
Pribnow boxConsensus sequence near the mRNA start-point of prokaryotic genes. See: TATA box.
primary antibodyIn an ELISA or other immunological assay, the antibody that binds to the target molecule.
Primary cellA cell or cell line taken directly from a living organism, which is not immortalized.
primary cell wallThe cell wall layer formed during cell expansion. Plant cells possessing only primary walls may divide or undergo differentiation.
primary cultureA culture started from cells, tissues or organs taken directly from organisms. A primary culture may be regarded as such until it is sub-cultured for the…
primary growth1. Apical meristem -derived growth; the tissues of a young plant. 2. Explant growth during the initial culture period.
primary immune responseThe immune response that occurs during the first encounter of a mammal with a given antigen.
primary immunodeficiencyA group of rare inherited disorders of the immune system, including adenosine deaminase deficiency, severe combined immunodeficiency (SCID), and…
primary structureThe linear sequence of residues making up a polymer such as a nucleic acid, polysaccharide or protein.
primary tissueA tissue that has differentiated from a primary meristem.
primary transcriptThe RNA molecule produced by transcription prior to any post-transcriptional modifications; also called a pre-mRNA in eukaryotes.
PrimerA short DNA or RNA fragment annealed to single-stranded DNA, from which DNA polymerase extends a new DNA strand to produce a duplex molecule.
primer walkingA method for sequencing long (>1 kbp) cloned pieces of DNA. The initial sequencing reaction reveals the sequence of the first few hundred nucleotides of…
Primitive streakThe initial band of cells from which the embryo begins to develop. The primitive streak establishes and reveals the embryo's head-tail and left-right…
Primordial germ cellA gamete, that is, a sperm or egg, OR a primordial cell that can mature into a sperm or egg.
primordiumA group of cells which gives rise to an organ.
primosomeA protein -replication complex that catalyses the initiation of synthesis of Okazaki fragments during discontinuous replication of DNA.
Prion-related protein (PrP)A normal protein, expressed in the nervous system of animals, whose structure when altered (by interaction with altered copies of itself) is the cause of…
PrivacyIn genetics, the right of people to restrict access to their genetic information.
pro-embryoA group of cells arising from the division of the fertilized egg cell or somatic embryo before those cells which are to become the embryo are recognizable.
pro-meristemThe embryonic meristem that is the source of organ initials or foundation cells.
pro-nuclear micro-injectionAn early, low success-rate method to achieve transgenesis in animals, involving the micro-injection of many gene copies into one of the two pro-nuclei of…
pro-nucleusEither one of the two haploid gamete nuclei, just prior to their fusion in the fertilized egg.
pro-phageThe genome of a bacteriophage integrated into the chromosome of a lysogenic bacterial cell, and replicated along with its host chromosome.
pro-toxinA latent, non-active precursor form of a toxin.
ProbabilityThe chance that an event occurs. It is usually expressed as a percent. Zero percent denotes impossibility, while 100% denotes certainty.
probandThe individual in a family in whom an inherited trait is first identified.
ProbeA sequence of DNA or RNA, labeled or marked with a radioactive isotope, used to detect the presence of complementary nucleotide sequences. See Nucleotide.
procambiumA primary meristem that gives rise to primary vascular tissues and, in most woody plants, to the vascular cambium.
processed pseudo-geneA copy of a functional gene which has no promoter, no introns and which, consequently, is not itself transcribed.
production environmentAll input-output relationships, over time, at a particular location. The relationships include biological, climatic, economic, social, cultural and…
production traitsCharacteristics of animals, such as the quantity or quality of the milk, meat, fibre, eggs, work, etc.
productivityThe amount of economically significant product generated within a given period of time from a specified quantity of resource.
Progenitor cellA progenitor cell, often confused with stem cell, is an early descendant of a stem cell that can only differentiate, but it cannot renew itself anymore.
progenyOffspring; the product of reproduction or replication.
progeny testingWith respect to discrete loci, the inference of the allelic state of an individual from the pattern of segregation among its offspring.
progesterone(proh-JES-tuh-RONE) A type of hormone made by the body that plays a role in the menstrual cycle and pregnancy.
programmed cell deathA type of cell death in which a series of molecular steps in a cell leads to its death.
ProkaryoteA bacterial cell lacking a true nucleus; its DNA is usually in one long strand. See Eukaryote.
prolactin(proh-LAK-tin) A hormone that is made by the pituitary gland (a pea-sized organ in the center of the brain).
ProliferationIncrease by frequent and repeated reproduction; growth by cell division.
PromoterAny person who, directly or indirectly, organizes or assists in the organization of a tax shelter or who participates in the sale of any interests in a…
Pronuclear injectionThe use of a fine needle to inject DNA into the nucleus of an unfertilized egg.
PronucleusEither of the two haploid gamete nuclei just prior to their fusion in the fertilized ovum.
proofreadingThe scanning of newly-synthesized DNA for structural defects, such as mis-matched base pairs. A functional activity of most DNA polymerase s.
propagationThe duplication of a whole plant from a range of vegetative materials; adapted for in vitro culture as micropropagation.
propaguleAny structure capable of giving rise to a new plant by asexual or sexual reproduction, including bulbils, leafbuds, etc.
prophaseThe first stage of nuclear division. The stage during which occurs in the first division of meiosis (see: leptonema, zygonema, pachynema, diplonema…
prostate cancer(PROS-tayt KAN-ser) Cancer that forms in tissues of the prostate (a gland in the male reproductive system found below the bladder and in front of the…
protamineA class of small basic proteins that replace the histones in the chromosomes of some sperm cells.
proteaseAn enzyme that cleaves peptide bonds that link amino acids in protein molecules.
protein(PRO-teen) A molecule made up of amino acids that are needed for the body to function properly.
protein crystallizationThe production of a pure preparation of a protein. In this form, the three-dimensional structure of the molecule can be determined.
protein engineeringGenerating proteins with modified structures that confer novel properties such as higher catalytic specificity or thermal stability.
Protein kinaseAn enzyme that adds phosphate groups to a protein molecule at serine, threonine, or tyrosine residues.
protein metabolic stepOne step in the chain of reactions that take place in an organism and dictate the composition of that organism.
protein sequencingThe process of determining the amino acid sequence of a protein. Usually achieved following initially partial hydrolysis of the protein into smaller…
protein synthesisThe creation of proteins from their constituent amino acid s, in accordance with the encoding gene DNA sequence.
proteinaceous infectious particleBelieved to be the agent responsible for the class of diseases called spongiform encephalopathies, including scrapie in sheep, bovine spongiform…
Proteinaceous infectious particle (prion)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…