What is Low Copy Number DNA?
With LCN DNA, Profiles Can Be Obtained from Very Small Samples
Maybe LCN DNA is the next frontier. It has proven helpful in cold cases but because of the small samples there are big risks of contamination and accuracy.
The Purpose of DNA Analysis
The purpose of DNA analysis is to prove individual identity or genetic relationships.
Back in 1985, the first genetic "fingerprint" was a miracle of science. Today DNA analysis is standard practice for defining paternity or maternity, predisposition to disease, embryonic health, criminal guilt or innocence.
DNA – Involvement and Exclusion Factors
Professor Allan Jamieson is Director of The Forensic Institute, Glasgow. In the online Journal for the Scottish Law Society describes the involvement and exclusion factors of DNA like this:
For a DNA profile 10 areas of DNA are analyzed, rather like examining only 10 shelves in a library. Maybe 10% of people have a Harry Potter book. Five per cent have Alice in Wonderland. Thirty per cent have A Brief History of Time (and 0.01% understood it!). The probability of someone having all three books is 1/10 x 1/20 x 3/10 = 3/2000, or approximately 1 in 666. You can see that no matter how many books you choose to include in the search, the probability of finding a person with all of those books will get smaller, but never reach 0.
Benefits and Dangers of DNA Evidence
He explains further that two features of DNA evidence that can be viewed as its major benefits also produce its greatest potential dangers: specificity and sensitivity.
- Specificity – how useful DNA is in telling people apart, usually expressed as the match probability.
- Sensitivity - a measure of how little DNA is needed to perform analysis and produce a profile.
Low Copy Number (LCN) DNA
LCN DNA was developed by the UK Forensic Science Service (FSS) in 1999. The technique, performed by only a few laboratories across the world, is extremely expensive but is necessary when only small amounts of DNA are recovered for analysis.
What is LCN DNA?
Low Copy Number (LCN) DNA analysis is like traditional DNA analysis. The purpose is the same: to try and match the DNA extracted from cells found at the scene of the crime.
Advantages of LCN DNA Profiling
The upside of this type of DNA profiling is that it allows a very small amount of DNA to be analyzed, even the DNA from just 15 to 20 cells.
Forensic investigators are able to target areas on items where it is believed that an offender may have transferred DNA through touch, like the residue from cells such as skin or sweat, left in a fingerprint.
Problems with LCN DNA
Because of the small amount of starting DNA, many more cycles of replication are necessary and contaminants will be also be replicated, creating a greater risk of inaccurate results.
A correct fingerprint identification on a fixed object, may establish that you were at a particular point, but DNA can be transferred from one person to another and from them to somewhere else the original person may never have been.
There are a limited number of providers of this controversial technology; testimony is only allowed in a few countries at present and because many samples come from “cold cases,” forensic scientists often work with degraded or sub-microscopic volumes of material.
Effects of the Omagh Bombing Outcome
After the acquittal on all charges of Sean Hoey in the 1998 Omagh Bombing Trial in Belfast, Northern Ireland in which 29 people died, the future of LCN DNA looks uncertain.
In the United Kingdom, the Association of Chief Police Officers (Acpo) announced that it was suspending the use of LCN testing in all future cases pending the outcome of a the Crown Prosecuting Services review. All current cases in the United Kingdom in which Low Copy Number (LCN) DNA testing forms part of the evidence will be now be scrutinized.
Forensic Expert Sounds a Warning
"They were warned about it," said Professor Jamieson, of the Glasgow-based Forensic Institute. He said the Midlands-based Forensic Science Service (FSS) which claimed that they were leading the field through their LCN DNA work should have been asking during the Omagh bombing Trial why no-one else, including the well-resourced FBI, was relying on the same technique.
Source:
LCN DNA - Devil in the Detail by Allan Jamieson from the Journal Online.
