DNA profiles for forensic use

Each of the chromosomes in your cells contains many sections of non-coding DNA – DNA that does not code for a protein, but contains areas called short tandem repeats (STRs). Each STR contains repeats of short sequences of bases, such as CATG in the sequence CATGCATGCATG.

If DNA is analysed for 10 different STRs on different chromosomes, there is only a one in a million chance that two people will have the same number of repeats in all of these STRs, except for identical twins.

This means that if the DNA profile (or fingerprint) for 10 STRs for a crime suspect matches the profile for the same 10 STRs from a sample found at the crime scene, there is a very high probability that they come from the same person. However, if the profiles differ for even one of the tested STRs, this cannot be assumed.

DNA is being used increasingly as evidence in court, but it is considered ‘circumstantial’ evidence and can only be used as proof with other supporting evidence. However, it has proven useful in establishing the innocence of suspects on its own.

Is DNA evidence infallible? Watch a story form the ABC's Catalyst program and decide for yourself: h ttp://www.abc.net.au/catalyst/stories/s1199805.htm

As seen on TV

Just like our favourite forensic science TV dramas, forensic scientists can analyse DNA samples from crime scenes and compare them with DNA samples from victims and suspects to help solve crimes.

However, unlike on TV, the techniques are a bit more complicated and take much longer than ten minutes – more like two weeks, in fact. And in a real forensic investigation, specialists would be performing specific tasks, rather than one small doing everything.

Lawyers and forensic scientists have also noted that people now have a distorted view of how forensic science is really used in criminal cases and believe that all forensic evidence is infallible.

Forensic profiling in Australia

Forensic profiling began in Australia in 1988, and has assisted police in thousands of investigations since. The Australian Government is in the process of setting up a DNA database of known criminals called CrimTrac. Only DNA profiles from convicted criminals (and not suspects) will be included on the database.

According to the Victoria Police, it takes approximately 2 weeks to obtain a full DNA profile from a tissue sample. This can be sped up in urgent cases, however there are many samples to process with several samples collected at each crime scene.

In Australia, forensic DNA testing is done at government laboratories, as well as at some universities and private organisations.

For more information about the actual process of DNA extraction and Interpretation, go to the Victoria Police website: http://www.police.vic.gov.au

Try solving a crime using DNA profiling - interactive

DNA testing of prison inmates

A number of crimes remain unsolved due to lack of evidence. The majority of crimes are committed by only a few people. Of these few, there are a number of repeat offenders. In the USA, England and New Zealand there are central DNA databases containing the profiles of all previously convicted people. This allows for a quick identification if they re-offend.

In Australia, the central database, CrimTrac, is likely to help solve some unsolved crimes. At the moment criminals in different states have different rights when it comes to DNA profiling. It is also an issue that has a lot of concerns surrounding it with some people feeling that to DNA sample inmates is a breach of legal rights.

For more information on CrimTrac, go to: http://www.crimtrac.gov.au/

Disaster victim identification

After a disaster such as a bombing or fire, it is often difficult to identify the victims. Forensic scientists are called in to identify the DNA obtained from body parts or teeth.

During the aftermath of the 2002 Bali bombing for example, relatives of victims were asked to send DNA samples from objects at home, such as a toothbrush, comb or item of clothing. So far, of the missing or deceased in Bali, 182 have been identified, including 88 Australians.

DNA profiling is just one of the identification methods used. In Bali, 12 people were identified using fingerprints, 115 people identified by methods including DNA, 100 identified by methods including dental records and 7 identified by methods including medical records.

More recently, Australian forensic experts have been sent over to Thailand to assist with the identification of bodies following the 2004 tsunami.

For information about Disaster Victim Identification, go to the Australian Federal Police website: http://www.afp.gov.au/

For more information on disaster victim identification in Bali, go to http://www.crimtrac.gov.au/dnabali.htm

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This means that if the DNA profile (or fingerprint) for 10 STRs for a crime suspect matches the profile for the same 10 STRs from a sample found at the crime scene, there is a very high probability that they come from the same person. However, if the profiles differ for even one of the tested STRs, this cannot be assumed. DNA is being used increasingly as evidence in court, but it is considered ‘circumstantial’ evidence and can only be used as proof with other supporting evidence. However, it has proven useful in establishing the innocence of suspects on its own. Is DNA evidence infallible? Watch a story form the ABC's Catalyst program and decide for yourself: h ttp://www.abc.net.au/catalyst/stories/s1199805.htm As seen on TV Just like our favourite forensic science TV dramas, forensic scientists can analyse DNA samples from crime scenes and compare them with DNA samples from victims and suspects to help solve crimes. However, unlike on TV, the techniques are a bit more complicated and take much longer than ten minutes – more like two weeks, in fact. And in a real forensic investigation, specialists would be performing specific tasks, rather than one small doing everything. Lawyers and forensic scientists have also noted that people now have a distorted view of how forensic science is really used in criminal cases and believe that all forensic evidence is infallible. Forensic profiling in Australia Forensic profiling began in Australia in 1988, and has assisted police in thousands of investigations since. The Australian Government is in the process of setting up a DNA database of known criminals called CrimTrac. Only DNA profiles from convicted criminals (and not suspects) will be included on the database. According to the Victoria Police, it takes approximately 2 weeks to obtain a full DNA profile from a tissue sample. This can be sped up in urgent cases, however there are many samples to process with several samples collected at each crime scene. In Australia, forensic DNA testing is done at government laboratories, as well as at some universities and private organisations. For more information about the actual process of DNA extraction and Interpretation, go to the Victoria Police website: http://www.police.vic.gov.au Try solving a crime using DNA profiling - interactive DNA testing of prison inmates A number of crimes remain unsolved due to lack of evidence. The majority of crimes are committed by only a few people. Of these few, there are a number of repeat offenders. In the USA, England and New Zealand there are central DNA databases containing the profiles of all previously convicted people. This allows for a quick identification if they re-offend. In Australia, the central database, CrimTrac, is likely to help solve some unsolved crimes. At the moment criminals in different states have different rights when it comes to DNA profiling. It is also an issue that has a lot of concerns surrounding it with some people feeling that to DNA sample inmates is a breach of legal rights. For more information on CrimTrac, go to: http://www.crimtrac.gov.au/ Disaster victim identification After a disaster such as a bombing or fire, it is often difficult to identify the victims. Forensic scientists are called in to identify the DNA obtained from body parts or teeth. During the aftermath of the 2002 Bali bombing for example, relatives of victims were asked to send DNA samples from objects at home, such as a toothbrush, comb or item of clothing. So far, of the missing or deceased in Bali, 182 have been identified, including 88 Australians. DNA profiling is just one of the identification methods used. In Bali, 12 people were identified using fingerprints, 115 people identified by methods including DNA, 100 identified by methods including dental records and 7 identified by methods including medical records. More recently, Australian forensic experts have been sent over to Thailand to assist with the identification of bodies following the 2004 tsunami. For information about Disaster Victim Identification, go to the Australian Federal Police website: http://www.afp.gov.au/ For more information on disaster victim identification in Bali, go to http://www.crimtrac.gov.au/dnabali.htm
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