| antigenic shift | Mutation, i.e., sudden change in molecular structure of RNA/DNA in microorganisms, especially viruses, which produces new strains of the microorganism; hosts previously exposed to other strains have little or no acquired immunity to the new strain; antigenic shift is believed to be the explanation for the occurrence of strains of microorganisms, such as the influenza virus, associated with large scale epidemics. (05 Mar 2000) |
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| antigen shift | Abrupt change in antigens expressed by a species or variety of organisms. Usually seen in microorganisms where the change may allow escape from immune recognition. Antigenic drift is a more gradual change. See: antigenic variation. (18 Nov 1997) |
| axis shift | Deflection of the electrical axis of the heart to the right or left of the normal. See: left axis deviation, right axis deviation, axis. Synonym: axis shift. (05 Mar 2000) |
| Balkan frame | An overhead frame, supported on uprights attached to the bedposts or to a separate stand, from which a splinted limb is slung in the treatment of fracture or joint disease. Synonym: Balkan beam, Balkan splint. (05 Mar 2000) |
| blocked reading frame | A sequence of DNA that cannot be translated into a viable protein; usually due to the interruption by one or more termination codons. Synonym: closed reading frame. (05 Mar 2000) |
| Bradford frame | An oblong rectangular frame made of pipe, over which are stretched transversely two strips of canvas; permits trunk and lower extremities of a bed-ridden patient to move as a unit. (05 Mar 2000) |
| gas shift process | A process in which carbon monoxide and hydrogen react in the presence of a catalyst to form methane and water. (05 Dec 1998) |
| reading frame | One of the three possible ways of reading a nucleotide sequence. As the genetic code is read in nonoverlapping triplets (codons) there are three possible ways of translating a sequence of nucleotides into a protein, each with a different starting point. For example: given the nucleotide sequence: AGCAGCAGC, the three reading frames are: AGC AGC AGC, GCA GCA, CAG CAG. (18 Nov 1997) |
| reading frame, open | An open reading frame in DNA has no termination codon, no signal to stop reading the nucleotide sequence, and so may be translated into protein. (12 Dec 1998) |
| chemical shift | Dependence of the resonance frequency of a nucleus on the chemical binding of the atom or molecule in which it is contained. See: chemical shift artifact. (05 Mar 2000) |
| chemical shift artifact | In magnetic resonance imaging, a dark band caused by a biochemical difference in resonant frequency of adjacent regions rather than a true anatomic separation. (05 Mar 2000) |
| chloride shift | When CO2 enters the blood from the tissues, it passes into the red blood cell and is converted by carbonate dehydratase to bicarbonate (HCO3-); HCO3- ion passes out into the plasma while Cl- migrates into the red blood cell. Reverse changes occur in the lungs when CO2 is eliminated from the blood. Synonym: Hamburger's phenomenon. (05 Mar 2000) |
| phase shift | <microscopy> A change in the phase relationship between two alternating quantities of the same frequency. (05 Aug 1998) |
| closed reading frame | A sequence of DNA that cannot be translated into a viable protein; usually due to the interruption by one or more termination codons. Synonym: closed reading frame. (05 Mar 2000) |
| phyletic shift | <ecology> A measurable change over time in a population which can be physical, morphologic, genetic, and/or behavioural. (09 Oct 1997) |