In this blog, I endeavor to create a forum for education and discussion regarding matters related to forensic DNA testing.  It is meant for attorneys, students, and the general public to ask questions and discuss topics and news articles.  I hope you will find it informative and worthwhile!


4 thoughts on “Welcome

  1. There are certainly situations in which it would be essentially untouchable in court (barring an absolute sample mix up or gross contamination event). For example, the finding of semen in an intimate sexual assault sample from the victim with a DNA match to a suspect with statistical significance of 1 in a quadrillion!

    However, what many people may not know is that DNA results actually come in a variety of types and significances. For example, a partial DNA result containing a mixture of DNA from multiple sources may only have the ability to eliminate 1 in 2 people in the population.

    Also, since even trace amounts of DNA can be detected, even if not in a detectable stain, the presence of DNA may not be significant even if the statistical power of the result is. It all depends upon interpretation context.

    In fact, it may not be clear who actually deposited the DNA in instances of DNA transfer. If I use a pen that belongs to someone else, a significant amount of the pen owner’s DNA may transfer to my hand. If I then touch my face after handling the pen….the other person’s DNA could transfer to my face. Thus, finding someone else’s DNA on my face in no way absolutely means that they physically touched me.

    1. Hi Clarissa. Great question. It is absolutely possible. As to how likely it is and how the DNA typing results would look, there are a number of factors. DNA testing of the object will likely show the DNA of both individuals in some ratio. So, the ‘vector’ or person transferring the DNA typically shows up as well. Of course if you touched a large bloodstain and transferred that to another object, DNA testing would likely only show the DNA type of the blood since there would be much more DNA from the blood than from your hand.
      But in transfer/touch DNA scenarios the amount of DNA is typically low. Couple that with the amount of DNA decreasing with each transfer: some is lost as it transfers to your hand, and not all of the DNA on your hand will necessarily transfer to the object.
      If your hand is particularly dry and doesn’t have a lot of DNA and the other person is particularly sweaty and has a lot of DNA on their hand, then the DNA results on the object may show a mixture of DNA with the other person being the major contributor.

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