Q&A: How are advances in DNA enabling breakthroughs in missing persons cases?

Why are advances in DNA forensics enabling breakthroughs in criminal and missing persons cases – even cold cases going back many years?

DNA technology, especially to identify remains and suspects in criminal investigations, has undergone remarkable advances in recent years.

Techniques now routinely available are more precise, easier to deploy, quicker in getting results, and less expensive. Moreover, it’s possible to work on small, even tiny, samples or where DNA is partially degraded. A large number of samples can be processed in a forensics lab with sophisticated data processing.

The technology is so reliable it is possible to identify an individual following exhumation decades after burial, and even to go back thousands of years analysing ancient DNA samples.

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Why is DNA so significant?

The human body is composed of billions of cells of many different types such as blood cells; hair, skin and bone and muscle cells. Almost all cells contain a nucleus with an identical copy of a person’s DNA (their genetic blueprint).

Because of this DNA from a person’s blood will be the same as that found in their saliva or hair roots. Half of our DNA is inherited from our mother and half from our father.

Who tests DNA samples in criminal and missing person cases on behalf of the State and the Garda?

Tests are carried out by DNA experts working with Forensic Science Ireland, a division of the Department of Justice based at Garda HQ in Dublin's Phoenix Park.

Though each person's DNA is unique, with current technology it is not practical to look at each difference. So FSI in its laboratory looks at 16 different areas of DNA, known to have a wide variance within the Irish population, Dr Edward Connolly, it's serious crime team manager explained.

The 16 areas, represented by 32 peaks in genetic profiles, contain short repeating sequences known as short tandem repeats (STR). The number of these repeating sequences varies between individuals.

DNA profiling involves analysing and measuring differences in length of STRs. An additional two peaks on the profile (labelled XY or XX) determines whether the person is male or female.

What has been the key advance?

The standard technology used to identify individuals is short tandem repeat (STR) analysis. It identifies “genetic markers” and was developed in the 1990s.

But forensic scientists now avail of a range of new technologies, while many of the processes previously carried out manually can now be done by robotics – especially in the way DNA is extracted, prepared and cleaned for profiling.

It then undergoes “quantification” - the amount of DNA is measured as an optimum amount is required for successful profiling. The DNA pieces targeted in profiling are copied many times, a process known as amplification. This makes profiling sensitive enough to generate a profile even from a barely visible blood stain.

Profiles are then generated using a technique known as capillary electrophoresis. At that point, it can be determined if there’s a match or not, according to Dr Connolly.

Familial DNA testing is different to conventional DNA testing, which looks for positive matches, like matching the DNA from a bloody glove to the DNA from a specific suspect. Crucially, a match can only be made if the suspect’s DNA can be collected, which makes it impractical for most cold cases.

But familial DNA searches, which are deployed on a case-by-case basis, look for partial matches, which could indicate that the sample comes from a sibling or a parent rather than the same person. That’s not enough to conclusively identify a person on its own, but it can give police a crucial lead that can result in further testing down the road.