| MRAP | alpha-2-macroglobulin; maximal resting anal pressure; mean right atrial pressure |
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| RAI | radioactive iodine; radioactive isotope; resident assessment instrument; resting ankle index; right ... |
| RE | radium emanation; readmission; rectal examination; reference emitter; reflux esophagitis; regional e... |
| REE | rapid extinction effect; rare earth element; resting energy expenditure |
| R-EEG | resting electroencephalography |
| back focal length | <microscopy> As measured on the principal axis, from the second lens vertex to the back focal point of the lens. It is not the equivalent of the focal length. (05 Aug 1998) |
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| bellows length | <microscopy> The distance from the eye point to the image plane in a photomicrographic apparatus. (05 Aug 1998) |
| bond length | This is the distance between the nuclei of two atoms which have formed bonds with each other. (09 Oct 1997) |
| passive length-tension curve | The relationship between passive tension and preload (rest length) for a muscle at rest. (05 Mar 2000) |
| required arch length | The sum of the mesiodistal widths of the permanent teeth from first permanent molar to first permanent molar. (05 Mar 2000) |
| restriction fragment length polymorphism | <molecular biology, technique> A method that allows familial relationships to be established by comparing the characteristic polymorphic patterns that are obtained when certain regions of genomic DNA are amplified (typically by PCR) and cut with certain restriction enzymes. The variation in the length of DNA fragments produced by a restriction endonuclease that cuts at a polymorphic locus. Such variations are generated by mutations that create or abolish recognition sites for these enzymes. This is a key tool in DNA fingerprinting, reflecting the existence of different alleles in the individual. Restriction fragment length polymorphism mapping is also used in plant breeding to see if a key trait such as disease resistance is inherited. In principle, an individual can be identified unambiquously by restriction fragment length polymorphism hence the use of restriction fragment length polymorphism in forensic analysis of blood, hair or semen). Similarly, if a polymorphism can be identified close to the locus of a genetic defect, it provides a valuable marker for tracing the inheritance of the defect. Synonym: DNA fingerprinting. Acronym: RFLP (12 Jan 1998) |
| restriction length polymorphism | Fragment length polymorphism, the existence of allelic forms recognizable by the length of fragments that result when the nucleotide chain is treated by a specific restriction enzyme that cleaves wherever a particular sequence of nucleotides occurs. A mutation in this sequence changes cleaving and hence the number of fragments. (05 Mar 2000) |
| greatest length | Measurement from the cranial to caudal end of the embryo prior to folding. (05 Mar 2000) |
| positive focal length | <microscopy> Any lens which converges parallel rays to a focus at the back of the lens is a positive lens and has a positive focal length. The focal length is measured from the second principal point of the lens to the point on the lens axis where the rays from an infinitely distant point are brought to focus. See: negative focal length. (05 Aug 1998) |
| crown-heel length | Length of an outstretched embryo or foetus from skull vertex to heel. See: Streeter's developmental horizon(s). (05 Mar 2000) |
| crown-rump length | In utero measurement corresponding to the sitting height (crown to rump) of the foetus. Length is considered a more accurate criterion of the age of the foetus than is the weight. The average crown-rump length of the foetus at term is 36 cm. (12 Dec 1998) |
| height-length index | The relation of the height to the length of the skull: (height × 100)/length. Synonym: height-length index, length-height index, transversovertical index. (05 Mar 2000) |
| spinal length | A measurement from the distal surface of the embryo where the plane passes through the developing eye (this is the cranial limit of the spinal cord) down to the rump. (05 Mar 2000) |
| negative focal length | <physics> The focal length of a negative lens. Parallel rays impinging on a negative lens can be traced to a virtual focus which exists on the same side of the lens as the impinging rays. The distance from the second principal point of the lens to this second focal point is measured on the same side of the lens as is the object. See: negative lens, focal length. (05 Aug 1998) |
| equivalent focal length | <microscopy> The focal length of the simple lens that has the same power as the compound lens. The stated focal lengths of microscope objectives are the equivalent focal length since their front and back focal lengths are very different. (05 Aug 1998) |