Secondary DNA Transfer Research Articles

Secondary and subsequent DNA transfer during criminal investigation

With the introduction of new multiplex PCR kits and instrumentation such as the Applied Biosystems 3500xl, there has recently been a rapid change in technology that has greatly increased sensitivity of detection so that a DNA profile can routinely be obtained from only a few cells. Research to evaluate the risks of passive transfer has not kept pace with this development; hence the risk of innocent DNA transfer at the crime-scene is currently not properly understood. The purpose of this study was to investigate the possibility of investigator-mediated transfer of DNA traces with disposable nitrile-gloves used during crime-scene examinations. We investigated the primary transfer of freshly deposited DNA from touched plastic, wood or metal substrates and secondary and tertiary transfer by a person wearing disposable nitrile-gloves and onto a third object. We show that with use of the new highly sensitive technologies available in forensic DNA analysis there is an enhanced probability to obtain a DNA-profile which has not been directly deposited on the object but is an outcome of one or more transfer events. The nitrile-gloves used by investigators during exhibit examination can act as a vector for DNA transfer from one item to another. We have shown that the amount of DNA deposited on an object affects the probability of transfer. Secondly, the type of substrate material that DNA is deposited onto has an impact on transfer rates.

DNA transfer during social interactions

Multiple DNA transfer has increasingly been brought up in court as potential means for the presence of the defendants DNA at the crime scene or on a piece of evidence. This has prompted several investigations into DNA transfer under very controlled and semi-controlled conditions, however little is published about DNA transfer in “uncontrolled” or real life situations.Here we examined the effects of multiple direct and indirect transfer of DNA within a small group of people and objects: three individuals participating in a social interaction of having a drink (jug of juice) together for 20min. At the end of the tests all the surfaces of interest were sampled and analyzed.In many instances the last person or the only person to come in contact with the object was the main or the only depositor of the DNA detected on it. The jug was a clear vector for secondary DNA transfer. Interestingly, in many instances the participants acted as vectors for foreign DNA transfer.

The Recovery and Persistence of Salivary DNA on Human Skin

Salivary DNA is encountered in many crimes, such as sexual assaults and murders. In this study, saliva from three male donors was deposited on the skin of three female recipients. The amount of male salivary DNA remaining on the female skin was measured over a 96-h period using the Quantifiler™ Y Human Male DNA Quantification Kit. In eight of the nine experiments, a full male DNA profile matching the donor was obtained even after 96 h. In addition, the study showed that the concentration of salivary DNA varied from donor to donor and from day to day. The efficiency of two recovery methods, wet and dry swabbing and minitaping, was compared. The results indicate the tapelift method gave higher DNA recovery. This study also examined the secondary transfer of salivary DNA from skin to fabrics. Cotton and polyester give higher DNA transfer than leather.

Investigation of secondary DNA transfer of skin cells under controlled test conditions

There is a paucity of data on the relative transfer rates of deposited biological substances which could assist evaluation of the probability of given crime scene scenarios, especially for those relating to objects originally touched by hand. This investigation examines factors that may influence the secondary transfer of DNA from this source, including the freshness of the deposit, the nature of the primary and secondary substrate and the manner of contact between the surfaces.The transfer rates showed that both the primary and secondary type of substrate and the manner of contact are important factors influencing transfer of skin cells, but, unlike other biological fluids, such as blood and saliva, the freshness of the deposit in most instances is not. Skin cells deposited on a non-porous primary substrate transferred more readily to subsequent substrates than those deposited on a porous substrate. Porous secondary substrates, however, facilitated transfer more readily than non-porous secondary substrates, from both porous and non-porous surfaces. Friction as the manner of contact significantly increased the rate of transfer.The findings of this study improve our general understanding of the transfer of DNA material contained in fingerprints that is left on a surface, and assist in the evaluation of the probability of secondary and further DNA transfer under specific conditions.

Secondary DNA transfer of biological substances under varying test conditions

This research investigates factors that may influence the secondary transfer of DNA. These include the type of biological substance deposited, the nature of the primary and secondary substrate, moisture content of the deposit and type of contact between the surfaces. Results showed that secondary transfer is significantly affected by both the type of primary substrate and the moisture (wetness) of the biological sample. Porous substrates and/or dry samples diminished transfer (with on average only 0.36% of biological material being transferred from one site to another), whereas non-porous substrates and/or wet samples facilitated transfer events (approximately 50–95% of biological material was transferred from one site to another). Further, the type of secondary substrate also influenced transfer rate, with porous surfaces, absorbing transferred biological substances more readily than non-porous ones. No significant differences were observed among the biological substances tested (pure DNA, blood and saliva). Friction contact between the two substrates significantly enhanced secondary transfer compared to either passive or pressure contact. These preliminary results will assist in developing general assumptions when estimating probability of a secondary DNA transfer event under simple conditions.

Investigation into “Normal” Background DNA on Adult Necks: Implications for DNA Profiling of Manual Strangulation Victims

Others have investigated the role that DNA profiling could play as a method for identifying the perpetrator of manual strangulation. These studies have demonstrated that it is possible to collect offender DNA from the skin surface of a victim following physical contact. It is not known whether nonself biological material is normally present on the skin surface due to adventitious transfer occurring during innocent everyday interactions. To test the hypothesis that detectable amounts of nonself DNA are normally present on the skin surface of healthy adult individuals due to the adventitious transfer of DNA occurring during normal day-to-day social interactions, we designed an experiment in three phases. Phase 1 was used to deduce which DNA collection, extraction, and amplification methods were suited to investigating this question. During phase 2, the neck surface of 24 healthy adult volunteers was swabbed. DNA was extracted using the QIAamp DNA mini kit and amplified using the SGM Plus PCR amplification kit, using 28 PCR cycles. The work carried out during phase 3 involved a simulated assault to investigate primary and secondary transfer of DNA during physical contact. It was found that 23% of neck areas swabbed during phase 2 of this investigation showed nondonor alleles in the resulting DNA profile, with 5% of areas showing six or more nondonor alleles. The results of phase 3 showed that primary, secondary, and zero transfer of victim and/or offender DNA could be observed after physical contact and that alleles from an unknown source could still be detected in this more controlled experiment. The data presented in this paper demonstrate that DNA profiles generated after swabbing the skin surface of healthy adults can include components of an unknown source, present due to adventitious transfer. These components, if present in large quantities, have the potential to interfere with DNA profile interpretation of swabs taken for the investigation of physical assault by DNA profiling.

Assessment of individual shedder status and implication for secondary DNA transfer

Low copy number DNA analysis offer the sensitivity to allow for analysis of minute amounts of DNA retrieved from touched objects. An experiment was designed to investigate secondary DNA transfer, and to assess the participants DNA shedder status. The aim was to investigate the implications of individual shedder status on secondary DNA transfer from handling items. We found that a persons shedder status – good, medium or poor – is of consequence in order to deposit enough DNA for a full profile. Furthermore, the vector was not always the one with the most dominant profile on an item, implying that secondary transfer could occur from a better shedder donor through handshaking or by handling the same item.

WITHDRAWN: Assessment of individual shedder status and implication for secondary DNA transfer

WITHDRAWN: Assessment of individual shedder status and implication for secondary DNA transfer

The tendency of individuals to transfer DNA to handled items

This research investigates factors influencing the transfer of DNA to handled objects and the process known as ‘shedding’. Volunteers were recruited to hold sterile plastic tubes using experiments originally designed by Lowe et al. [A. Lowe, C. Murray, J. Whitaker, G. Tully, P. Gill, The propensity of individuals to deposit DNA and secondary transfer of low level DNA from individuals to inert surfaces, Forensic Sci. Int. 129 (2002) 25–34]. Transferred cellular material was collected from the tubes and STR profiles generated using the AmpFlSTR SGM Plus™ multiplex with 28 and 34 PCR cycles. Volunteers were asked to hold the tubes with each hand, and to participate in a series of handwashing experiments. The DNA profiling results obtained from the transferred skin cells were compared. An attempt was made to characterize the volunteers as ‘good’ or ‘bad’ shedders and to establish which, if any, of the experimental variables were associated with ‘good’ shedding. Our results suggest that many factors significantly influence shedding, including which hand an individual touches an item with and the time that has elapsed since they last washed their hands. We have found that it may be more complicated than previously reported to categorise a person as being either a ‘good’ or a ‘bad’ shedder and that if truly ‘good’ shedders exist they may be significantly rarer than some have estimated. In the current research no ‘good’ shedders were observed in a group of 60 volunteers. Given these results, it seems that rather than being applied to individual forensic cases, knowledge of shedding characteristics will be most useful in providing general background data for the interpretation of trace DNA evidence.

The propensity of individuals to deposit DNA and secondary transfer of low level DNA from individuals to inert surfaces

We have shown that there is a difference between individuals in their tendency to deposit DNA on an item when it is touched. While a good DNA shedder may leave behind a full DNA profile immediately after hand washing, poor DNA shedders may only do so when their hands have not been washed for a period of 6 h. We have also demonstrated that transfer of DNA from one individual (A) to another (B) and subsequently to an object is possible under specific laboratory conditions using the AMPFISTR ®SGM Plus™ multiplex at both 28 and 34 PCR cycles. This is a form of secondary transfer. If a 30 min or 1 h delay was introduced before contact of individual B with the object then at 34 cycles a mixture of profiles from both individuals was recovered. We have also determined that the quantity and quality of DNA profiles recovered is dependent upon the particular individuals involved in the transfer process. The findings reported here are preliminary and further investigations are underway in order to further add to understanding of the issues of DNA transfer and persistence.

Secondary Transfer of Seminal Constituents

ABSTRACTThis paper reports a case of rape in which the forensic DNA analysis of a penile swab revealed a DNA mixture in the epithelial fraction consistent with the complainant and suspect, as well as the detection of spermatozoa from a second male in the sperm fraction. Subsequently the semen present on the penile swab was shown to match the DNA profile of the complainant's boyfriend. By considering the DNA results obtained in both the female and male fractions, the Court concluded that the suspect had sexual intercourse with the complainant and was guilty of rape. The case illustrates that secondary DNA transfer, i.e. the passing of DNA through an intermediary, can be important in solving crime.

A Systematic Analysis of Secondary DNA Transfer

The Nature letter by R. van Oorschot and M. Jones (1) addressed two topics: the primary transfer of DNA from person to person or to various objects, and the secondary transfer of DNA through an intermediary. Forensic scientists have described the primary transfer of DNA and other biological evidence for many years. However, the authors also reported detecting secondary transfer of DNA from an object to a person's hands, which could adversely affect DNA typing in the forensic context. The prospect of secondary transfer raises questions of interest to both the legal and forensic communities. Therefore, we sought to evaluate parameters potentially leading to secondary DNA transfer. Our data do not support the conclusion that secondary transfer will compromise DNA typing results under typical forensic conditions.