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Small DNA Samples for Criminal Forensics

By: Ian Murnaghan BSc (hons), MSc - Updated: 15 Jan 2015 | comments*Discuss
 
Dna Crime Forensics Touch Dna Lcn Dna

Since discovering DNA, the technology and ability to analyse it has changed significantly. Many of the older challenges, such as efficiency and timeliness, have been virtually swept aside as better DNA analysis techniques have been developed over the years.

Smaller Sample Sizes From Skin Cells

Still, some sample sizes are so small and come from such a brief encounter or transfer that they can appear seemingly useless. That is, until recently when a technique was developed for obtaining and analysing these particular DNA samples.

Dubbed 'touch DNA', the technique represents the way in which police remove samples from only a mere few cells that remain after a person has touched something such as clothing. As humans, we shed enormous numbers of skin cells each day and these cells are transferred to clothing and other objects.

Touch DNA vs LCN DNA

One area of confusion is the difference between touch DNA and Low Copy Number (LCN) DNA. With LCN DNA, Forensic Scientists are able to analyse a very tiny sample of DNA, with anywhere from five to 20 cells.

However, a touch DNA sample will be analysed in much the same manner as a Sample From Blood or another common type of sample. It is also generally well recognised in a criminal investigation that goes to court proceedings. Commonly, PCR analysis is used to process a touch DNA sample.

Pinpointing a Suspect

So long as a form of contact occurs, there is virtually always an exchange of some kind. Assuming that during a crime, the person committing the crime transfers a reasonable amount of skin cells on some object at the scene of the crime – and if the item is identified and collected rapidly after the crime – then DNA analysis can yield information about the criminal.

Where is Touch DNA Located?

In theory, it's located virtually anywhere and everywhere. Our skin cells are transferred all of the time but in terms of what has already been accomplished, touch DNA has been used on samples from all sorts of objects ranging from a car's steering wheel to a person's clothing.

A challenge is that skin cells from a number of innocent people will still remain at the crime scene so the real test is for an investigator or forensics expert to decide where a sample is best collected.

Collecting Touch DNA

Touch DNA samples are extremely small and more challenging to obtain than other kinds of DNA samples for analysis. At the very basis of the technique is an investigator's ability to actually 'spot' where a suitable sample can best be found. A sampling approach needs to be used for obtaining the most cells possible to yield successful results.

A swab may be taken or even a piece of clothing cut off for collection of cells. Other collection methods include scraping and using tape to life off the cells.

Using Touch DNA

Touch DNA has been used in some well-publicised cases, such as the JonBenet Ramsey case in the United States. It's still not a widely used type of DNA collection for analysis but it certainly can be of significance in collecting skin cells and helping to pinpoint a perpetrator.

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