Laundry in a washing machine as a mediator of secondary and tertiary DNA transfer.

The aim of this work was to investigate the possibility of secondary and tertiary DNA transfer during laundry. The modes of transfer tested were mixed and separate laundry of worn and unworn garments in household and public washing machines. In addition, the possibility of a background DNA carry-over from a washing machine's drum was investigated. In the mixed (worn and unworn garments washed together) laundry experiment, 22% of samples from new unworn socks with no traceable DNA prior to experiment produced DNA profiles post-laundry. In the tertiary DNA transfer experiment performed in a public washing machine (unworn garments only), no detectable DNA profiles were observed. Samples collected from the internal drum of 25 washing and drying machines did not produce detectable STR profiles. The implications of these results are discussed in the context of forensic DNA casework analysis. Graphical Abstract ᅟA real-life scenario of secondary DNA transfer between worn and unworn garments during machine washing has been evaluated. Experiments demonstrated this scenario is possible (22% of samples) and may in fact result in high quality DNA profiles. On the contrary, testing washing machine's interior for deposition of biological material between separate washing cycles to serve as a mediator of tertiary DNA transfer resulted in no DNA profiles.

A search for obligatory paternal alleles in a DNA database to find an alleged rapist in a fatherless paternity case.

A sexual assault case resulted in a pregnancy, which was subsequently aborted. The alleged father of the fetus was unknown. Maternal and fetal types were obtained using the 11-locus AmpFℓSTR(®) SGM Plus(®) kit. The national DNA database was searched for the paternal obligatory alleles and detected two suspects who could not be excluded as father of the male fetus. Additional typing using the AmpFℓSTR(®) Minifiler(™) kit, containing three additional autosomal loci, was not sufficient to exclude either suspect. Subsequent typing using the PowerPlex(®) 16, containing four additional loci, and Y-Filer(™) kits resulted in excluding one suspect. Searching a database for paternal obligatory alleles can be fruitful, but is fraught with possible false positive results so that finding a match must be taken as only preliminary evidence.

STR typing of formalin-fixed paraffin embedded (FFPE) aborted foetal tissue in criminal paternity cases.

Sexual assault or rape cases occasionally result in unwanted pregnancies. In almost all such cases the foetus is aborted. A forensic laboratory may receive the foetus, the placenta, or paraffin embedded abortion material for paternity testing. Obtaining a foetal profile DNA from a foetus or placenta may not be successful due to the age or condition of the tissue. Moreover, maternal contamination of placental material will invariably result in a mixed DNA profile. However, the use of properly screened abortion material from paraffin blocks will almost always result in obtaining a foetal DNA profile. Furthermore, foetal tissue fixed in paraffin blocks does not require special conditions for submission and storage as required to preserve fresh foetal or placental tissue. As hospitals routinely prepare foetal tissue in paraffin blocks, which should be readily obtainable by forensic laboratories, these samples would appear to be the preferred choice for paternity testing.

The use of adhesive tape for recovery of DNA from crime scene items.

The selection of the appropriate method of collection of biological material from crime scene items can be crucial to obtaining a DNA profile. The three techniques commonly used for sampling items are: cutting, swabbing, and taping. The tape sampling technique offers an advantage, in that it enables the collection of a potentially highly informative source of DNA, shed epithelial cells, from selected areas on crime scene items (the inside fingers of a glove, for instance). Furthermore, surface collection of biological material by taping reduces co-sampling of known PCR inhibitors such as clothing dyes. The correct choice of tape for crime scene item sampling is important. Not all tapes are suitable for biological trace evidence collection as well as DNA extraction. We report on one tape that met both these criteria. Three different cases are presented which demonstrate the usefulness of adhesive tape sampling of crime items. Finally, the advantages of the tape collection technique are discussed and guidelines for preferred areas of tape sampling on various casework items are presented.