Before you start reading about fascinating crime scene investigations and riddle solving, you might be interested in how the success story of the genetic fingerprint started and what DNA-analysis are done in forensics today. If so, this blog is exactly what you need!
How it all started
At the beginning of the 1980s huge progress was made in the analysis of DNA. Genetic fingerprinting (you can read about the genetic fingerprint here) was invented in the early 1980s by Alec Jeffreys, Peter Gill and Dave Werrett who were working for the Forensic Science Service in the UK. The first patent however for this method was stated in 1983 by Glassberg.
Alec Jeffreys invented the method in 1984. He was looking at X-ray images of digested and marked with radioactive Probe-DNA from his lab staff realizing that they all differed. He assumed that these unique patterns could be used to identify individuals. He used this method first publicly to prove the family relationship of a boy from Ghana. His family migrated to the UK, but after a trip to Ghana, the boy was not allowed back in the UK as he didn’t have his passport. Alec Jeffreys was asked if he could prove that this boy really was the son of the family and not a nephew. He analysed DNA of the mother and the boy in question as well as assumed siblings of the boy and prove that he was a biological son.
It didn’t take long before this method was applied in the first crime scene case in 1986. Two girls were raped and murdered in the Leicestershire area with a similar modus operandi in 1983 and 1986. There was a suspect called Richard Buckland who also confessed. Jeffreys was asked to analyse sperm samples collected from the victims and compare them with Buckland’s DNA. Surprisingly the DNAs didn’t match. So, the police asked men in a certain age range to give a DNA sample. 4000 men were tested but no one matched. Six months later a man called Collin Pitchfork was overheard in a pub, stating that he sent someone else to do the testing to evade the analysis. The police got a sample from him and voila the DNA matched. Pitchfork was arrested in 1987 and sentenced to life in prison in 1988.
Although this sounds like a major success story this method still had its downfalls:
- You needed a fairly amount of a body fluid
- The method was time intensive and expensive
- You needed a suspect to compare the DNAs
Scientific developments necessary for today’s success
The invention of the Polymerase Chain Reaction by Kary Mullis in 1987 was a crucial step in genetic analysis. As it amplifies DNA it enlarges the amount of DNA and makes it visible. This was the basis for being able to analyse DNA of every biological trace. Nowadays due to very efficient DNA extraction methods, efficient PCR reagents and highly sensitive analysis machines DNA out of hair, bones, skin cells, even down to a single human cell can be analysed.
In 1990 the analysis method for the genetic fingerprint was changed from digestion to amplifying and analysing Short Tandem Repeats (read this blog to get to know more about STRs).
Both the PCR and the STR usage were improved over the years. The analysis method of the genetic fingerprint got way cheaper, more sensitive, and highly accurate.
Nowadays you can purchase kits which can deliver a DNA result after 2 hours. Also, these kits ensure that you will obtain the individual genetic fingerprint as there are always a lot of markers included and it is assured that everything used is DNA free.
How to identify a stain from a crime scene without a suspect
In 1995 the Forensic Science Service established a DNA database saving genetic fingerprints of suspects as well as crime scene stain profiles. In 1998 the FBI followed with the so called CODIS database. The UK DNA database holds 6.6million profiles from individuals and crime scene samples, the CODIS database holds 14,541,796 offender profiles, 4,341,864 arrestee profiles and 1,103,683 forensic profiles. You can imagine that this is helpful if you have a crime scene and stains with good DNA profile. You can upload the new profile in the database and search for it.
Why are the crime scene investigators wearing these space suites?
As we already mentioned the methods of forensic DNA analysis got more and more sensitive. Also, the methods of forensic sciences got more and more sensitive too. As on crime scenes the investigators are searching for evidence, this might be biological material of the perpetrator or victim. As this is human material, another human of course can contaminate the crime scene with its own material, this might be a hair you lose, skin flakes, tiny drops of saliva you lose when you speak and so on. In times where the genetic fingerprint was new you needed a lot of body fluid, so the police contaminating these samples was hardly possible. But of course, they were wearing gloves to not contaminate real fingerprints (this technique already was used at the beginning of the 20th century). Nowadays a single, even degraded, cell will be enough to contaminate your result. That’s why as much caution as possible is carried out at the crime scene: disposable protective coveralls with a hood, disposable gloves, facemasks, tacky mats before you enter the crime scene (when possible), reduce conversations and so on.
Moreover, all the used collection materials like swabs, tubes, tapes, and bags, all the materials used in the lab like scalpels, scissors, pipette tips, PCR plates etc. need to be DNA free to minimize the risk of contamination.
Of course, as long as people are still handling the samples, mistakes may arise, that’s why modern DNA laboratories need to have a quality management system and have to prove to a state department (in the United Kingdom this department is called United Kingdom Accreditation Service) that all necessary precautions are taken and that there are mechanisms to track and trace mistakes and handle them. These days every DNA expert is aware of the pitfall of contamination and due to quality management systems, software support during resulting, employee databases and severe checks of plausibility, contaminations can be detected.
The future of forensic DNA-analysis
Just to let you know, research in forensic DNA analysis is still going on. One focus is getting the lab method on the street by building machines that can extract and analyse DNA at the crime scene, the so-called rapid DNA testing devices. Also based on sequencing methods we are now able to distinguish individuals even more, even get insides on physical traits or the geographical descendance of a person. But we will cover more information on these topics in upcoming blogs.
Success story forensic DNA analysis
There are thousands of cases solved by DNA analysis, not all of them are as spectacular as e.g., the glove in the OJ Simpson case or the case of the Golden State Killer. But DNA analysis is useful in all different kind of cases. We will provide you with some spectacular examples in upcoming blogs, but we will also cover the lesser-known cases which are also a part of the forensic DNA success story. Moreover, next to the STRs of your genetic fingerprint there is also the hidden treasure of mitochondrial DNA in your cells and the Y-chromosome in biological male individuals. These both can also be used for forensic DNA analysis. We will cover this in upcoming blogs, so stay tuned!