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DNA Transfer events


Previously, I discussed the circumstances that might persuade defense attorneys to explore using a DNA expert. One of these perplexing circumstances is driven—in part—by astonishing advances in the sensitivity of DNA detection. Recent DNA technologies, referred to as LOW COPY NUMBER (LCN) analysis (also called ‘low template’, ‘high sensitivity’, or ‘trace DNA’ analysis) allows crime lab analysts to PUSH DNA DETECTION CAPABILITIES to the point at which useful data is obtained from only 15-20 cells, or perhaps as few as just 1 or 2 cells. Such extremes in testing sensitivity are causing courtroom battles to emerge, due to the mere LIMITATIONS OF SCIENTIFIC ACCEPTANCE. Adding fuel to this fire, these conflicts intensify significantly when DNA expert witnesses fall into the trap I prefer to call the 'touch DNA misnomer'.

Embracing the phrase "touch DNA" on the witness stand, with NO scientific proof that touching ever occurred, is the 2011-2012 idiotic equivalent of yesteryear's 'DNA Fingerprinting misnomer'. STR-based forensic DNA typing technology involves NO examination of fingers. Nor does it relate to latent print examinations, an entirely separate forensic discipline. Why do some individuals insist upon confusing society with terms that simply do not apply?


In 1910, Dr. Edmond Locard, professor of forensic medicine at the University of Lyons, France, was the founder of the world's first forensic science lab. This great scientist was also the first forensic scientist to formally emphasize the importance of transfer events in the investigation of crimes.

Dr. Locard's incredible intuition evolved into the time-tested Locard Exchange Principal, stating that "Every contact leaves a trace." Locard's principal became universally accepted over forty years BEFORE James Watson and Francis Crick proposed the first accurate model of the DNA double helix. The exchange principal was also widely embraced over seventy years BEFORE Colin Pitchfork became the first person to be identified and convicted of a crime, using the power of DNA typing.

As an insult to the celebrated history of Dr. Locard's principal, *some* modern day prosecutors—with the support of their crime lab analysts—attempt to downplay the plausibility of DNA transfer events. Despite the fact that the crime scenes are crawling with CSI's who enthusiastically center their efforts on Locard's teachings, some courtroom comedians are allowed to drone on with their ridiculous folly of reasoning. JURORS PLEASE TAKE NOTE: TRACE MATERIAL EXCHANGE EVENTS ARE NOT THE PRODUCT OF OVERACTIVE SCIENTIFIC IMAGINATIONS.

The ludicrous efforts to downplay Locard are readily invalidated. EVERY WINTER—new strains of common cold viruses and influenza viruses succeed with their inevitable campaigns of terror throughout earth's human population. How do these prosecutors and their supporting scientists (and I am using the term ‘scientists’ loosely) suppose these viruses are so swiftly spread from human to human?

During a particularly frosty stretch of weather, look around, visit various homes, take a stroll through the local mall. Nasal cavities are draining, infected individuals are coughing and sneezing. Crumpled up facial tissues are strewn EVERYWHERE. Those tissues came from the people who are actually considerate enough to use a Kleenex every now and then—rather than their shirt sleeves OR THEIR HANDS.

Trillions of viral particles are spread by the actions of the infected, ….to door handles, telephones, computer keyboards, car keys, steering wheels, stairway railings, currency, vending machines, TV remote controls, pens, pencils, clothing, bedding, the list is endless. Each year, we are BEGGED by the Centers for Disease Control to “Wash your hands!” Any healthy person, who fails to wash his hands, and makes the mistake of rubbing his own tired eyes, ….well, ….you do the math. It takes a number of days for viral particles to establish a foothold in a human respiratory system.

DNA differs very little from viruses. Yes, our genetic molecules are much more friendly, and not very invasive. DNA causes no sore throats, no runny noses, and no coughs. Beyond that, DNA and viruses are quite similar in that they are both submicroscopic clumps of matter. Transfer events DO occur with BOTH forms of matter. Please do not let any courtroom snake oil representatives succeed in convincing you otherwise.

Today's state-of-the-art DNA detection technology can decipher a full DNA profile from less than one BILLIONTH of a gram of DNA. One way to grasp such extraordinarily tiny amounts of DNA is to visualize the mass of material in a standard packet of artificial sweetener. These packets contain one gram of material. Imagine setting aside 1/1000th of a single packet and disposing of the remaining 999 parts. The spec of powder set aside would weigh one milligram. Now imagine setting aside 1/1000th of this milligram and discarding the remainder. You now have one microgram of material (which is 1/1 millionth of the original sweetener packet). This amount of material cannot be clearly seen without the use of a microscope. By some means, you must now set aside 1/1000th of your microgram of artificial sweetener-this is one nanogram, or 1/1 BILLIONTH of the original starting material. One nanogram of DNA is PLENTY of genetic material for generating a FULL DNA profile. The astonishing sensitivity of forensic DNA typing technology does not diminish the fact that we are indeed working with a profoundly tiny mass of DNA.

Scientific debates focusing on the mechanisms of casual/incidental transfer events, involving such tiny amounts of DNA, are far from settled. In December 2010, some of the world's most renowned authorities on forensic trace DNA (Roland Oorschot, Kaye Ballantyne, and R. John Mitchell), published a REVIEW in Investigative Genetics. Quoting these authors directly from the "Transfer Issues" section of the review:

"Greater effort needs to be made by police/crime investigators to investigate how a DNA sample arrived at the location where it was found, as well as by scientists to better understand the impact of activities on the relative amounts of DNA from particular sources at a crime scene. In some instances, it is possible to derive the chain of events that led to a trace DNA sample being present at a crime scene - for example, prior visits to the scene or the known use of an item. Awareness of these variables, and their impact on transfer events, will assist in weighting the likelihood of proposed alternative scenarios." 

In 2010, Allan Jamieson and Georgina Meakin of The Forensic Institute (Glasgow, UK), published an article in The Barrister Magazine entitled: "EXPERIENCE IS THE NAME THAT EVERYONE GIVES TO THEIR MISTAKES"

The following is a quote from this article:

"The examination of evidence for handler DNA can reveal DNA of people who have, or have not, handled the item; the stronger profile may, or may not, be the person who last handled the item; An inference of direct contact between an individual and the item may or may not be supportable, depending on the circumstances of the case. In other words, we did not know enough to make any sensible scientific judgements as to how DNA came to be on an item." 

Later, the article continues:

"Frequently, the underlying hypothesis is that touching, or direct contact, is a more likely scientific explanation for the finding of a DNA profile on an item than indirect contact. This to the extent that it may be described as providing ‘extremely strong’ support for direct versus indirect transfer.  In our view, such an opinion on DNA transfer is not supportable based on case experience or on the available scientific research."

Finally, a 2009 article in Law Officer (a journal for police and law enforcement) is entitled: 'TRANSFER THEORY IN FORENSIC DNA ANALYSIS'. The author, Suzanna Ryan, arrived at the conclusion:

"Obviously, the inadvertent transfer of DNA is an area that should be further studied. Since so many of the available journal articles present conflicting information, more work is needed to see how likely it is to both transfer and detect DNA in a secondary or even a tertiary fashion, especially considering the sensitivity of modern forensic DNA analysis."

It is vital to keep in mind that the average adult human sheds approximately 36,000 skin cells every 60 seconds. This number varies broadly among individuals, as there are profound differences between those who can be characterized as 'good shedders', and others who are 'poor shedders'.

A single drop of saliva, expelled during a cough or a sneeze, will contain approximately 500,000 salivary epithelial cells. Forensic Biologists can attest to the fact that 500 to 10,000 nanograms of DNA are routinely recovered durng collection of a single oral swab. Once again, recall that ONLY ONE NANOGRAM is optimal for generating a complete DNA profile. This mass of DNA can be readily extracted from as few as 200 cells. This tiny number of cells could sit-nearly invisible-upon the very tip of a toothpick.

How many falsely accused individuals have been wrongfully imprisoned as a consequence of a few hundred cells finding their way to an incriminating location?

The next article is entitiled:

DNA Mixture Interpretation versus Misinterpretation

Michael J. Spence, Ph.D.


December 30, 2011


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