Thursday, August 6, 2015

History of DNA profiling

History of DNA profiling

Prof Sir Alec Jeffreys

DNA profiling, as we know it today, was developed thanks to two independent breakthroughs in molecular biology that occurred at the same time on different sides of the Atlantic. In the USA the polymerase chain reaction (PCR) was invented by Kary Mullis, while in the UK 'DNA fingerprinting' was being discovered by Professor Sir Alec Jeffreys at the University of Leicester.

In its earliest incarnation this technique was performed by restriction of 0.5–10μg extracted DNA using the restriction enzyme HinFI, followed by Southern blotting hybridisation designed to bind to multiple 'minisatellites' present in the restricted DNA.

This multi-locus probing (MLP) technique would result in probes binding to multiple independent DNA fragments at the same time giving rise to the traditional 'bar-code' pattern that is often visualised when we think of forensic DNA analysis, even today. Differences in the number of times the probe sequence is repeated in each DNA fragment forms the basis of the individual patterns observed on the autoradiogram image.

The first DNA profiling conviction


DNA was first used to aid a criminal investigation by Professor Jeffreys in 1986. This investigation used DNA fingerprinting techniques to link semen stain samples, collected from two rapes/murders that had occurred three years apart in 1983 and 1986, in a small village in Leicestershire, UK. The probability of this match occurring by chance was calculated as 5.8 x 10-8. This result not only linked the two crimes and secured the conviction of the perpetrator Colin Pitchfork, but also exonerated an innocent man implicated in the murders and led to the first mass screening project undertaken for DNA profiling in the world.

New techniques developed


Although accurate and reproducible, this original method of analysis required the use of a large amount of high quality DNA, which is not always recovered during forensic investigations. Two big breakthroughs occurred during the late 1980s and early 1990s that would form the basis of DNA profiling techniques as they are recognised today.

An alternative class of DNA marker, the microsatellite or short tandem repeat (STR) marker and an alternative method for DNA visualisation, PCR amplification and fluorescent labelling would greatly increase the sensitivity of DNA profiling methods and increase their use for criminal investigation.


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