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Jeffreys, Sir Alec (John)

dna sample bars specific

(1950– ) British biochemist: originator of DNA fingerprinting.

Jeffreys studied biochemistry and biochemical genetics at Oxford and in 1977 joined the department of genetics at the University of Leicester. In that year he discovered, with R Flavell (1945– ), the existence of introns in mammalian genes (introns are sequences of bases within DNA that do not code for a protein).

Jeffreys later realized that some very variable, and repeated, parts of the human genome (the full DNA sequence) are highly characteristic of individuals and so can be used for identification purposes. The number of these repeats is specific for each individual (except identical twins), half of them being inherited from the father and half from the mother. The method is valuable in criminal cases for linking an individual with a scene-of-crime sample and a variant of it is applicable in some paternity and immigration disputes. First proposed by Jeffreys in 1984, it was much used in the USA from 1987. A DNA profile can be got from a small sample of material (semen, blood or other tissue) which may be on clothing and can be years old. The sample is extracted to give its DNA; this is fragmented by enzyme action, the fragments are separated by gel electrophoresis and these are then radioactively labelled. A bar-code-like pattern, with its bars differing from one another in density and spacing and each derived from a DNA fragment, is the result and can be set beside the pattern obtained by similar treatment of a specimen from, for example, a suspected rapist. Bars of the same size and position in the gels point to the samples having the same genotype. The process can be repeated, say, four times, each time using a radioactive label for a specific DNA sequence, to give a ‘multilocus genotype’ print.

A chance match between the prints of two different people is widely held to have a probability of only about one in a million, although this near-uniqueness has been disputed since 1990 by some population geneticists; the problem is unresolved. Despite this, many lawyers see the technique as ‘the prosecution’s dream and the defence’s nightmare’.

Jeffries, Herb (1911–) [next] [back] Jasper, John(1812–1901) - Minister, orator, Chronology, Decision for Ministry

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