DNA fragments are separated through a capillary electrophoresis machine at the Division for Biological Evidence at Rikshospitalet in Oslo (formerly the Institute of Forensic Medicine).
DNA fragments are separated through a capillary electrophoresis machine at the Division for Biological Evidence at Rikshospitalet in Oslo (formerly the Institute of Forensic Medicine).

This is how DNA analysis has been revolutionized over the last decade

A number of technological advances enable forensic geneticists to detect tiny amounts of biological material that a perpetrator has left at a crime scene.

DNA technology was central to a dramatic recent decision by Norway’s Attorney General to acquit a man, Viggo Kristiansen, who was convicted 20 years ago for the rape and murder of two girls in Kristiansand, in an area called Baneheia.

The initial DNA results from two decades ago suggested that there was DNA from two men.

New investigations of the DNA evidence showed several traces from one of two men charged in the case, Jan Helge Andersen. Andersen has argued that Kristiansen was the main attacker, and that he had nothing to do with the attack on the older of the two girls who were murdered. Andersen was convicted of the murder of the younger girl and sentenced to 19 years in prison.

But newly unearthed findings showed there was no DNA at all from Kristiansen, which cut the legs out from under Andersen’s defense.

According to a report from TV 2 (link in Norwegian), the then section leader at the Institute of Forensic Medicine claimed that the samples had been destroyed. But in 2010, employees found almost 200 test tubes with DNA from the Baneheia case in a freezer.

These tests have now yielded completely new answers.

Can extract more from biological material

Over the last ten to twenty years, there has been a gradual revolution in the methods used to analyse DNA. Many technological innovations mean that biological material can reveal more than ever before.

“Now we can extract much more information from less and less material,” says senior engineer Mariam Mjærum Bouzga at the Department of Forensic Medicine at Oslo University Hospital.

The department has a separate section for forensic genetics in criminal cases.

Bouzga would not answer questions about the Baneheia case, but discussed DNA analysis on a more general basis.

Can distinguish between close relatives

By analysing biological material from a crime scene where a possible criminal act has taken place, forensic investigators are able to extract more information today than in the past, she said to sciencenorway.no.

“We analyse several areas —markers — on the DNA strand. That gives us more specific information than before regarding who has left the biological material,” she said.

But the DNA can’t give investigators information about a person’s physical characteristics, so they don't know who the individual is until they get a reference sample for comparison.

With the information obtained from today's analyses, investigators can distinguish between close relatives, but not identical twins.

Identical twins originate from the same egg and sperm cell and thus have identical DNA profiles.

Previously, DNA analysis methods were not as sensitive as they are today.

Much less material needed

Forensic scientists need a much smaller amount of biological material now than before, Bouzga said.

“Twenty years ago, we had to have so much blood or semen to extract DNA that it corresponded to a visible stain,” she said.

Now, however, they are able to obtain information from a much smaller amount of cells. The amount needed is so small that it’s invisible to the naked eye.

The reason why forensic scientists need much less biological material now is due to improvements in all of the links in the analysis chain.

Everything has improved, from material protection methods, to how the cell nuclei is cracked open so the DNA can be extracted, and the various parts of the DNA analysis itself. Now they can duplicate a specific selection of markers on the DNA strand and read that area.

In other words, they can copy specific areas from the DNA that they are interested in.

“This means that we can now read information from a microscopic sample that is specific to individuals, which we could not do before,” Bouzga said.

Easier to detect differences between siblings

We inherit DNA from our biological parents, half from our mother and half from our father.

DNA consists of four letters, A, T, C and G, which are repeated in various combinations in a long strand.

“You and your siblings have many combinations in common. But there are differences that we can more easily detect today,” Bouzga said.

“Now we look at 23 different areas on the DNA strand, as well as one area for gender,” Bouzga said.

More than 20 years ago, forensic scientists analysed far fewer areas on the DNA strand compared to today. At that time, only ten markers were used.

This meant it could be more difficult to distinguish between close relatives when determining whether biological material came from a suspect.

Now the analysis' are more accurate, and they can determine with a greater degree of probability that the material was left by a specific suspect — or the individual’s identical twin.

“An identical twin will have identical DNA,” Bouzga said.

In all cases, investigators must have DNA with which they can compare their sample, whether it’s from a suspect who voluntarily supplies DNA, or from the person’s DNA that is part of a criminal record.

Two methods of analysis can establish identity

Forensic scientists generally use two different types of DNA analyses. One, STR analysis, is used routinely, while the other is used in special cases as an additional analysis.

Both methods can establish a reliable identity.

Simply put, one method involves seeing how short or long the repeats of specific letter combinations are.

“We can see if the combinations have been repeated ten or eleven times, for example. This makes it very specific to an individual,” she said.

This method is called an STR analysis, where STR stands for short tandem repeats — short fragment repeats, she explained.

The Y chromosome

With the second analysis, the experts can get more detailed information.

This method is called MPS analysis and means that they can also read the letters that are contained in the DNA.

“We can find the length of a word,” she said.

The combinations provide so much information that it is very specific to an individual.

Men inherit their Y chromosome in its entirety from their father. Thus, DNA analyses of the Y chromosome do not provide information that is specific to an individual. But they provide information about the DNA that is passed down from father to son for generations.

“Mutations, changes, can occur in the DNA on this chromosome, as in other areas on the DNA strand,” Bouzga said.

Research in this field has shown that there are some areas on the Y chromosome where mutations occur more frequently than others. They are called fast mutating regions.

Today, several of these areas are included in the analysis panel when forensic investigators analyse the male sex chromosome. This enables the detection of mutations that occur between generations from father to son.

The cells also contain mitochondria, with their own DNA, which is inherited from mother to child. Both girls and boys inherit this from their mother.

Requirements for safeguards

The combination of all these techniques has made the overall analysis better, Bouzga said.

But no matter how good the analysis methods are, forensic geneticists are dependent on the DNA in both new and old biological material being isolated and stored in such a way that the quality does not deteriorate, meaning that it is not destroyed or broken down.

The DNA also has to be protected from contamination, meaning that the sample is protected from biological material that is inadvertently supplied by those who secure and handle the material after it has been taken from the crime scene.

“When it comes to new material, the police and others who secure and handle biological material are subject to strict requirements, including a requirement to have protective equipment, and methods and control mechanisms to prevent contamination,” she said.

And that it is possible to discover contamination, if it does happen.

Old material

Investigating old material can be a challenge, because there are many elements that can influence it, and which can be difficult to control. This is especially true for how the material is kept and stored.

DNA extracts are stored in a freezer, at minus 21 degrees. They can be taken out when needed for new analyses.

These samples can still pose a challenge if they have been secured at a time when requirements for protective equipment and working methods were different from today.

Other biological material must be kept dark, dry and cool.

But still, the quality will degrade and be lost over time.

Translated by Nancy Bazilchuk


Read the Norwegian version of this article at forskning.no

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