Friday, July 6, 2012

Dr. Sir Alec Jeffreys: Forensic Rock Star #2

Sir Alec Jefferys

DNA: The First Exoneration and Conviction

By: Joseph Giacalone
In my first Forensic Rock Star post, I highlighted the important contributions of Edmond Locard. Today's post will continue with the Forensic Rock Stars that have shaped the world of criminal investigations. Dr. Sir Alec Jeffreys is the reason why investigators all over the world search for evidence that contains DNA, the genetic blueprint of all human life. His discovery led to the transformation of how law enforcement manages crime scenes, how evidence is identified, secured and packaged properly.

Ashworth / Mann
Many people erroneously believe that the first time DNA was used to solve a crime was in the United States. It wasn't. In a small town in England known as Enderby, two teenage girls, Lynda Mann and Dawn Ashworth, were raped and murdered a few years apart in the same general vicinity. The police were limited on what they could derive from genetic material left at crime scenes. Analysis of the semen found at the scene provided the perpetrator's blood type as "A."  

Not only did this case get the first conviction based on DNA, but it also exonerated the first person, Richard Buckland, who initially confessed to murdering Dawn Ashworth. The police sought the help of Dr. Alec Jeffreys and his discovery of DNA profiling. Dr. Jeffreys's findings also included that no two person have the same DNA profile, except identical twins. The police suspected that Buckland was responsible for both murders, however, Dr. Jefrreys confirmed that Buckland was not the killer of either woman - the DNA profile said so. Armed with the profile the police asked all men in the area to submit a sample for testing against the profile. Thousands of blood samples were taken and tested but no match. The police were stumped, until they received a phone call about a man in a local bar claiming to have been paid to take the test for someone. After questioning the man, Colin Pitchfork was arrested and subsequently convicted. This time the confession was backed by the DNA profile. Recently, Colin Pitchfork has had his appeal denied.   
Colin Pitchfork /

Types of DNA

There are two types of DNA that are found in the body: Nuclear and Mitochondrial. However, not every cell in the body contains nuclear DNA. Nuclear DNA is the preferred finding by investigators because it contains genetic material from both parents. Mitochondrial DNA (mtDNA) does not have a nucleus and therefore does not contain genetic material from both parents. When investigators only have mtDNA, they must find a match that is derived from the maternal side. The way I always remembered it was M (mtDNA) is derived from Mom.

What is CODIS and how does it work?

CODIS is the acronym for the Combined DNA Index System. It is a nationwide system of storing and securing DNA samples. Inside of CODIS, two additional databases can be found: The Forensic Database and the Convicted Offender Database. It is easier to remember them as such: The Convicted Offender Database is the "Known" sample database and the Forensic Database contains the samples from crime scenes where the perpetrators are "Unknown." Because it is a nationwide system, each state has developed its own DNA Index System to alleviate conducting nationwide searches for what is more likely, local suspects.

How should DNA Evidence be Packaged?

All evidence that may have body fluids such as blood, saliva, semen, etc., must be packaged in paper and never in plastic. Unfortunately, law enforcement learned the hard way from all of those years that evidence was put in plastic security envelopes. Plastic over time degrades the sample due to moister buildup, rendering the sample useless in most cases.

Related Articles:

Familial DNA the Savior for Cold Cases?
New York State Votes to Expand DNA Database
Colorado's New DNA Law Paying Immediate Dividends


  1. Hi Joe.

    Great post! I love the idea of forensic rock stars. I wonder what Sir Alec would think?

    I hope you don't mind my addition of a few constructive comments to add to the story:

    The question of uniqueness of a DNA profile, although suggested by Sir Alec Jeffreys' work, is not so straightforward. It's not technically correct that all forensic DNA profiles, with the exception of identical twins', are unique. Only if forensic DNA profiling examined a person's entire complement of DNA (their genome) and compared it to all other genomes, would it be established that their profile was unique. We can infer that there's a good chance of genome uniqueness and it's now thought that this is also true for identical twins who, it's been shown, do have comparatively small differences.

    The reality is that forensic DNA profiling examines only a select few regions of the genome. In the current UK system, we examine 10 areas of DNA and an additional sex test, although other systems such as that in the US, examine more regions. To give an analogy for sense of scale, if the genome is described as a large library, then forensic DNA profiling could be likened to reading 10 books from that library (or a few extra ones in other systems). This means that we can't be sure of uniqueness, and it's the reason that DNA matches are never considered to be conclusive evidence. Instead, they're described in terms of the likelihood of matching, had the DNA not originated from the matching person, but from someone other than and unrelated to them. However, as you point out with the elimination of Richard Buckland, when DNA doesn't match, a person can be excluded as the source of DNA. There are some extremely rare circumstances when this is not quite true, but I won't elaborate on them here for fear of sending you to sleep on account of geek overload!

    What's a little more interesting is the reason that nuclear DNA is gained from both parents but mitochondrial DNA is only inherited from your mother. Nuclear DNA exists in the cell nucleus. Every cell starts off with a nucleus, but some cell types, such as red blood cells lose their nuclei. (That's right, all the nuclear DNA in blood exists in the white cells.) Mitochondrial DNA exists in a set of structures within the cell called the mitochondria. The mitochondria are the cell's energy producers. In sperm cells, the mitochondria are packed into the tail, powering movement and allowing sperm to swim. At fertilisation, when a sperm enters the egg, its tail drops off and all the male mitochondrial DNA is lost. The embryo only carries mum's mitochondrial DNA from the egg's mitochondria.

    Finally, in relation to exhibit packaging, the moisture buildup inside plastic packaging allows the growth of microorganisms on exhibits that renders them useless. Microorganisms, such as bacteria and fungi, feed on biological material in the sample, breaking down DNA. However, if you take away the moisture or freeze the samples to slow down the growth of microorganisms, samples can be preserved.

    I really enjoyed your post. Who's the next forensic rockstar in the series?

    Best wishes,
    Sue :-)

    1. Thanks Sue! By far the most informative and interesting response I ever received. I woul love for you to do a post. Great explanation-you make it sound so esy.