Biological evidence

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When examining a scene or an item of evidence it is very important to be aware of any biological evidence. This is because biological evidence is forensically very important because it can make a direct link between a suspect and the scene or item using DNA profiling.

         One of the most useful pieces of biological evidences is blood. It is possible to easily extract DNA from a blood sample which will produce a DNA profile which can be a direct link to the person it belongs to. Firstly, the sample has to be identified as possibly being blood using a presumptive test. Currently there are many different types but a common one is the Kastle-Meyer test. This reacts with haemoglobin resulting in a colour change and can detect blood diluted down by 1 in 1x104 (Johnston et al, 2008). This technique also has the advantage that it does not degrade any DNA allowing DNA analysis to take place afterwards (Bittencourt et al, 2009) Newer techniques are being produced using anti-primate antibodies which only react with primate haemoglobin. These techniques, such as Hexagon OBTI, have the advantage that blood from other species, such as a domestic pet, will not give a positive result saving time and money. (Johnston et al, 2008)

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         After a positive presumptive test has been established then it needs to have a confirmatory test to prove it is defiantly blood. This can be done with either a Takayama or Teichmans test. These tests react with the haemoglobin to produce crystals which can be identified under a light microscope (Virkler & Lednev, 2009a). A possible new confirmatory technique for blood is by using Raman spectroscopy. This is a useful technique because it can be used on very small samples and does not destroy any of the sample (Wael et al, 2008) (Virkler & Lednev, 2008). If you only have a small sample of blood then you might not be able to afford to destroy any of it you can use this method to confirm that it is blood.

Semen is another body fluid often found at a crime scene. Current methods for detection of blood include the presumptive Acid Phosphate test. This reacts with the acid phosphate in the semen resulting in a colour change. However, other materials contain acid phosphate such as virginal secretion which will give false positives. (Virkler & Lednev, 2009a). To confirm the presence of semen, either microscopy or a Prostate Specific Antigen (PSA) test in carried out. In microscopy the sample is stained and viewed under a microscope for any spermatozoa. However, this will not work in males who do not produce Spermatozoa. (Virkler & Lednev, 2009a). Another method is using a PSA test. This is an assay which reacts with PSA, which is only in sufficient quantities in semen (Pang & Cheung, 2007). A more recent test has been developed which looks for semenogelin using a RSID-Semen Test. This has an advantage over PSA because it is possible that semenogelin is more stable. (Pang & Cheung, 2007)

Like blood, Raman spectroscopy could possibly be used as a confirmatory test for semen. Virkler & Lednev (2009b) have shown that it is possible to use Raman spectroscopy to confirmatory test for semen. The advantages of this method are similar to blood in that it is non-destructive to the sample. Also, portable Raman spectrometers are readily available which means this technique can be easily carried out at a crime scene saving negative samples being brought back to the laboratory.

         The tests mentioned above are all carried out one at a time. This can waste time, sample and money if you have to carry out each one. Also, once the presence of blood or semen has been confirmed it is sent off for DNA analysis. However, due to the cost in both time and sample, sometimes the confirmatory step is missed out and the sample is sent straight away for DNA analysis. (Hansen et al, 2009) This means that samples that do not contain biological stains are being analysed for DNA which is expensive. Juusola & Ballantyne (2005) have developed a method for identifying and confirming a body fluid from the mRNA present. Each different type of cell expresses different genes and therefore has different quantities of mRNA species present in them. By identifying the mRNA present through PCR it is possible to identify the biological stain.

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         This has the advantage that you can test for more each sample (blood, urine, semen etc.) at the same time saving both time and sample. It also will detect virginal secretions (Juusola & Ballantyne, 2005). Another advantage is that it will detect semen from men who do not produce sperm as well as men who do produce sperm in one test. (Hass et al, 2009) However for the technique to work you need to have intact mRNA in the sample. It is possible to extract mRNA from stains up to 15 years old(Hass et al, 2008) however it has been shown that rain has an effect on the amount of mRNA present and can the time of recovery dramatically. For example, enough mRNA can only be collected within three days from blood exposed to rain instead of 30 days (Setzer et al, 2008). Hansen et al (2009) has shown that it is possible to identify the biological sample using microRNA (miRNA). miRNA's are only 20-25 base pairs long and are therefore less likely to be degraded through the environment and time.

By using mRNA and miRNA, a forensic scientist can be a lot more efficient as he can confirmatory test each stain for all body fluid types using just one test meaning they can spend less time on each item. Also less of the sample will be wasted, allowing more to be available for DNA testing.

References

  • Bittencourt, E. Soares-Vieira, J. Angeramis, N. Silva, C. Hirschfeld, R. Iwamura, E. (2009)The analysis of biological samples from crime scene for a future human DNA profile confrontation. Effects of presumptive test reagents on the ability to obtain STR profiles for human identification. Forensic Science International: Genetics Supplement Series
  • Hanson, E. Lubenow, H. Ballantyne, J. (2009)Identification of forensically relevant body fluids using a panel of differentially expressed microRNAs. Analytical Biochemistry 387, pp 303-314
  • Hass, C. Klesser, B. Maake, C. Bär, W. Kratzer, A. (2008) mRNA profiling for body fluid identification by reverse transcription endpoint PCR and realtime PCR. Forensic Science International: Genetics 3, pp 80-88
  • Hass, C. Muheim, C. Kratzer, A. Bär, W. Maake, C. (2009) mRNA profiling for the identification of sperm and seminal plasma. Forensic Science International: Genetics Supplement Series
  • Johnston, E. Ames, C. Dagnall, K. Foster, J. (2008) Comparison of Presumptive Blood Test Kits Including Hexagon OBTI. Journal of Forensic Sciences. 53 (3), pp 687- 690
  • Juusola, J. Ballantyne, J. (2005) Multiplex mRNA profiling for the identification of body fluids. Forensic Science International 152, pp 1-12
  • Pang, B. Cheung, B. (2007) Identification of human semenogelin in membrane strip test as an alternative method for the detection of semen. Forensic Science International 169, pp 27-31
  • Setzer, M. Juusola, J. Ballantyne, J. (2008)Recovery and Stability of RNA in Vaginal Swabs and Blood, Semen, and Saliva Stains. Journal of Forensic Science, 53 (2), pp. 296-305
  • Virkler, K. Lednev, I. (2008) Raman spectroscopy offers great potential for the non-destructive confirmatory identification of body fluids. Forensic Science International 181, pp e1-e5
  • Virkler, K. Lednev, I. (2009a) Analysis of body fluids for forensic purposes: From laboratory testing to non-destructive rapid confirmatory identification at a crime scene. Forensic Science International 188, pp 1-17
  • Virkler, K. Lednev, I. (2009b) Raman spectroscopic signature of semen and its potential application to forensic body fluid identification. Forensic Science International 193, pp 56-62
  • Wael, K. Lepot, L. Gason, F. Gilbert, B. (2008) In search of blood-Detection of minute particles using spectroscopic methods. Forensic Science International 180, pp 37-42