Cars & Other Vehicles

How long until touch DNA is gone? How much can be found?

In January of 2012 I wrote this article.Since that time, there have been many more articles written on the subject.The article is still useful when it comes to touch/transfer DNA.

Modern technology can lead to the identification and apprehension of a criminal by simply picking up an object or touching a surface.The analysis of "touch" DNA samples is the norm in the world of the forensic DNA analyst.

In the past few years, the number of touch DNA evidence items being submitted to the lab for analysis has skyrocketed, as well as the amount of journal articles about touch and DNA transfer.The purpose of this article is to update the reader on the latest touch and transfer DNA research and attempts to answer some of the most common questions that are asked regarding the topic.

A review of what touch DNA is and how it arrives on an object.Touch DNA is the transfer of genetic material from one person to another.Since it is known that the top-most layers of skin are dead, where does the touch DNA come from?According to the experiments performed by Kita et al, small amounts of fragmented DNA are present on the surface of the skin and they theorize that these fragments of DNA may be constantly removed from the cornified layer of skin.The presence of sweat helps contribute to the DNA profile obtained from touch DNA samples, according to research by Quinones and Daniel.The researchers showed that free-floating DNA fragments not encapsulated in the cell nucleus contribute greatly to the total amount of DNA present in a sample.nucleated cells were present in sweat samples taken from volunteers.After centrifugation to collect the cellular material, the supernatant is generally discarded, because many DNA extraction methods don't use the portion of the sample where CNAs are found.In the Kita et al article, they show how changing the methodology to use the DNA from the cell-free nucleic acids has the potential to increase the amount of DNA available for profiling.

Given a certain set of circumstances, how much DNA is expected to be transferred is one of the most common questions asked.This is a difficult question to answer as there are so many variables involved.The baseline idea of how much DNA might be recovered from touched objects can be provided from various studies.The amount of DNA needed to make a full profile with most amplification kits is approximately 1 ng, and partial profiles can be obtained with even less starting material.There is a summary of the various amounts of DNA detected in published studies.

It's important to remember that not every contact leaves enough DNA behind to yield a profile.The short answer is no, but sometimes I am asked, "If a person touched this object, would they have left DNA behind?"The transfer of DNA is not always done through contact alone.Lowe and his colleagues found that 12 of 30 subjects transferred little to no DNA to a sterile tube after handling for 10 seconds.A female test subject transferred a DNA profile that was not her own to a sterile tube.Only 19 strangulation samples yielded DNA results, according to a research article by Rutty.Only 7 of these showed signs of both the victim and the suspect.A majority of people failed to leave behind their genes on a sterile tube that was held for 10 seconds.A study by Raymond et al found that of the 252 trace casework samples, 112 did not produce a profile.Only 26% of the contact traces had a DNA profile suitable for entry into the Swiss database, according to a study by Castella and Mangin.

Improvements in the technology and methodology of DNA analysis have arisen as a result of the date the study was published and what methodologies were used at that time.Many of the earlier touch and transfer DNA articles report results from samples amplified with Profiler Plus and/or COFiler which are older amplification kits that used a larger amplification volume as compared to the standard 25 l reaction volume.In addition, the majority of the earlier papers list volumes from 50 to 200 l.If this concentration step had been performed in the past, additional DNA profiles would have been developed if the extract was concentrated to a small volume.Many labs have the option of using specialized techniques to maximize their results.In addition to concentrating one's DNA extract, the analyst may also have the option to increase the injection time on the Capillary Electrophoresis instrument thus increasing the amount of DNA entering the capillary for detection.The amplification reaction can be added to with the addition of Taq and the BSA.The option to reduce the amplification volume even further has been shown to increase the sensitivity of the reaction.Additional amplified product can be added to the sample tube for injection after the post-amplification clean-up steps.It is important to be aware of possible interpretational difficulties that may arise from using these techniques, as each of these steps has the possibility of increasing the amount of DNA observed on the electropherogram.

In 1997 initial research by van Oorschot and Jones showed that the amount of DNA detected did not change regardless of how long an object was held.The study he and Kisilevsky conducted found that the amount of DNA transferred to a substrate is not dependent on handling time.If an item is handled many times, then an increase in the amount of DNA present may be expected.

Sometimes DNA is transferred to an object via touch, but other times it is not.There are known factors that can affect the amount of DNA available for transfer.

There is a Shedder status.Some people who tend to shed skin cells at a higher rate than others may be considered good shedders.It is nearly impossible to determine if a person is a good or bad shedder as repeated tests on the same person on different days can give very different results.There is hand washing.If a person hasn't washed their hands in a while, there will be more shed cells on the surface of the hands.Personal habits.Some people tend to touch their face, eyes, nose, and hair.More often than others, the DNA from those areas is transferred onto the next thing that is touched.The process was described as loading the fingers with DNA.There is a type of contact.Pressure and friction can be related to how much DNA is transferred onto an object.An increase in the amount of pressure applied tends to lead to more DNA being transferred, and the application of friction to the contact increases the transfer even more.Substrate.It is better to collect and retain skin cell DNA on rough surfaces than it is on smooth surfaces.The smooth areas of a gun's grip andtrigger are processed for prints while the rougher areas are tested for DNA.spirationSweat increases the amount of DNA available for transfer.It is thought that this may happen for two reasons.It is possible for sweat to collect cells along the way and wash them to the surface of the skin.The study by Quinones and Daniel showed that sweat contains cells and nucleic acids which can be used for transfer to an object.

How long does touch DNA last?There is no easy answer when it comes to touch DNA.This is becoming an increasingly important area of research as defense attorneys begin presenting arguments to suggest that touch DNA found at a crime scene can be explained by the suspect's presence at the scene at an earlier time.

Imagine a scenario in which a male DNA suspect is located on a brick wall outside of the home of a murder victim.The DNA is negative for blood, semen, and saliva and appears to be from skin cells.How did it get there?The suspect fled the crime scene by climbing over the brick wall, according to the prosecution.It is possible that the victim's blood evidence is found on the wall.The suspect previously lived at the home in question and is a relative of the murder victim.Is it possible that the suspect left his skin cell DNA when he lived at the home or visited his relative?The counter top of the jewelry store was broken into.The masked man placed his ungloved hands on the counter in order to jump over it.The results yield a mixture of the suspect's genes.According to defense attorneys, the client had visited the store before to look for a new ring for his wife.Which scenarios are accurate?

Only one study addresses the persistence of touch DNA.Raymond and his team investigated the persistence of DNA at crime scenes.They applied theffy coat to wooden window frames, pieces of vinyl, and control samples consisting of glass microscope slides.The chance of recovering DNA from an outdoor crime scene decreases significantly over time with two weeks being the major drop-off point for most of the samples.The control samples were able to have full profiles developed even after six weeks, showing up good digital images from microscopes.The time between the offense and the collection of the evidence was included in the table of results obtained from actual touch DNA casework samples.It is interesting to note that two of the three evidence items with greater than 50 days between offense and collection yielded DNA profiles.A bag in a drug case that was collected at 55 days after an offense yielded a full DNA profile with 4.2ng of DNA present and fingerprints on a laptop.The stability of touch DNA on fabrics is briefly discussed in one study.Volunteers rubbed their fingers between a sample of fabric.The fabric samples were subjected to amplification after being exposed to light on a window ledge.For up to 36 days after transfer, Linacre et al were able to generate nearly complete Powerplex 16 profiles.

It is important to gather as much information as possible to determine if a touch DNA profile could have been left behind prior to the alleged incident.There is an item of evidence.It is expected that rough objects will collect more skin cell DNA than smooth items.Does the evidence have cracks, crevices, or grooves that are protected from skin cell DNA?A gun grip, buttons on a cell phone, and a computer keyboard are examples.Is the item exposed to the elements or is it expected to last longer?The item may have been touched by many people.Or only by very few (a weapon or a steering wheel)?It is not possible to give an exact time-line on how long the evidence will last.It is clear that more studies are needed in order to answer questions about the persistence of touch DNA evidence that are often asked by investigators and attorneys alike.

Is it possible that my client's DNA arrived on the item of evidence via secondary transfer?Is it possible that someone's DNA could be found on an item even though they never touched it?The answer is yes, based on several recent studies.

When I shake your hand, my DNA is transferred to your hands.You transfer my genetic material to a knife.

I pick up and swing a wooden bat and transfer my DNA to the handle of the bat, you pick it up the same way and a sample of your hands shows me.

I use a bath towel that is wrapped around a gun and my DNA is found on the gun as a secondary transfer from the towel.

After the short correspondence between van Oorschot and Jones in Nature in 1997 about examples of secondary transfer, there was a study by Ladd et al in 1999.They conclude their paper by saying that secondary transfer was not observed.A closer look shows that low-level secondary transfer was observed.Minor peaks from the second individual were observed.This is the primary transfer.The increased sensitivity common with today's methods and techniques would likely have yielded an even greater appearance of secondary DNA transfer.Studies show that the transfer of DNA can happen under different circumstances.

The study looked at the transfer of touch DNA onto wood, glass, and fabric.Mixed DNA profiles were obtained in 10% of the samples.There are two instances in which a major male/minor female profile was obtained from samples held by female individuals.The results are similar to a study done by Lowe et al in 2002 in which an individual held hands with another individual and then handled a pre-sterilized plastic tube and transferred only the second individual's DNA to the tube, none of their own.

Goray et al performed a detailed study on the transfer of skin cells.The researchers found that freshly transferred skin cells transferred to a secondary surface more easily than dried transfers and that non-porous primary substrates generated increased transfer rates.Transfer rates double when pressure is involved in the transfer, as opposed to a passive contact, and transfer rates increase even further when friction is used.The amount of primary DNA deposit that would be necessary to allow for the secondary transfer of 1 gram of DNA was estimated by the authors.The authors state something.

The amount of original deposit will vary depending on a number of factors.If a fresh sample was deposited on cotton and then subjected to pressure contact with a secondary surface that is hard and non-porous, like plastic, a minimum deposit of 385ng of DNA is needed for 1ng to have been.

An example of how secondary transfer could affect the interpretation of a case was shown by Sarah Jones and the Centre for forensic Investigation at the Body Fluids Conference.If non-intimate contact resulted in the transfer of DNA to a male volunteer's underwear and penis, it was done by Jones and Scott.Even though there was no direct contact between the female and the male, one of the scenarios resulted in the transfer of their genes to each other.1 minute of face-touching, 3 minutes of handholding and immediate urination was involved in the scenario.During the 15 minute period between non-intimate contact and urination, no female DNA was found on either the underwear or penis of the male volunteers.

It is possible for DNA to be transferred from person to object.A recent study by Goray et al discusses the transfer of DNA within forensic exhibit packaging.The results of their study were startling.The authors packaged mock evidence samples and handled them in a way that mimicked the movement of evidence from the crime scene to the laboratory.The transfer of skin cells from a swab to a plastic tube was shown in the results.Blood stains and saliva from cigarette butt were found to transfer to other items in the same container, as well as onto the interior of the packaging itself.Bloodied knives showed the transfer of material from the tip of the knife to other areas.

It is not possible to determine who handled an item last due to the variable nature of DNA transfer.Who might have handled an item the most is the same thing.It doesn't mean that they must have handled the phone last because one person's DNA profile is more prevalent on an item like a cell phone.It doesn't mean that the phone must be theirs because more of their genes are present.It could be that one of the factors that increase the amount of DNA transferred is in play.They may be a good shedder or they may have some personal habits which lead to a greater amount of DNA on their hands, for example.

How long until touch DNA is gone? How much can be found?

Related Posts: