DNA fingerprinting

In 1985, Jeffreys and colleagues published a series of papers highlighting the high level of polymorphism in the number of repeats found at certain minisatellites, and their utility in defining a unique pattern for a particular individual - an approach dubbed 'DNA fingerprinting' (Jeffreys et al. 1985b, 1985c). They found that a particular 33 bp repeat present in a short minisatellite of four tandem repeats within an intron of the myoglobin gene could be used to generate a probe that detected a number of other minisatellites scattered across the genome. This 'multilocus' probe hybridized simultaneously to multiple polymorphic minisatellites when used in a Southern blot of restriction enzyme digested DNA, giving a highly specific pattern of multiple bands dependent on the numbers of repeats in particular minisatellites.

Jeffreys and coworkers noted a core sequence within the 33 bp repeat shared between the minisatellites the probe identified (GGGCAGGAXG). A given multilocus probe was highly specific: when a single probe (designated '33.15') was used the probability of a match between unrelated people was less than 3 x 10-11; when two different probes ('33.15' and '33.6') detecting particular sets of minisatellites were used this fell to less than 5 x 10-19 (Jeffreys et al. 1985c). The approach radically altered forensic practice, being used initially in criminal investigations (Fig. 7.2) (Gill and Werrett 1987) and extensively in establishing paternity (Jeffreys et al. 1991) and immigration cases (Jeffreys et al. 1985a).

A limitation of the approach for analysing scene-of-crime material such as blood stains is the need for relatively large amounts of good quality DNA (several micrograms). The use of simpler single locus probes

Dna Fingerprint
Figure 7.2 Forensic use of DNA fingerprinting. DNA fingerprinting was used in a rape case to identify the DNA fingerprint of suspect 1 as exactly matching that of the semen specimen from a vaginal swab of the rape victim. Reprinted with permission from Strachan and Read (2004).

(specific to a single minisatellite) allowed increased sensitivity with band detection down to 10 ng of DNA and avoided some of the difficulties of comparing between blots (Tamaki and Jeffreys 2005). The use of DNA fingerprinting and genetic profiling is now fundamental to forensic practice and utilizes a range of different types of human genetic variation and amplification/detection techniques, with a more recent focus on short tandem repeats (microsatellites) but also Y chromosome and mitochondrial polymorphisms, SNPs, and copy number variation.

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