Help To Understand Inadvertent DNA Transfer

Of course your DNA could end up on something that was part of a "crime", but it would be because you touched something, bled on something, got some fluids on something, etc.; then then someone else deposits DNA on the same item. Lets say you picked up a candlestick at your friends house, someone comes and murders her with it. Now, potentially your cells are on it. This is well known, and results in what is called a mixed sample - and a complicated problem, as in forensics, mixed samples are often misinterpreted, actually what we call "overinterpreted", made to mean more than they are able to. I can show you an example where Culhane does this. It is not a 'key' piece of evidence, but the fact that she does it speaks to her credibility.

This secondary transfer cells that you are talking about is highly unlikely. i.e. someone touching something, picking up someone else's DNA and depositing it on something else. Perhaps if you literally stuck your hand in someone's blood and smeared it on something else; etc. But transferring the kind of cells that would be called "touch DNA" no.

I don't know what you source is for "article after article" stating this is.

You also need to differentiate from DNA and cells/tissue/fluid. If two cigarette butts are in a package together and there are cells could possibly move from one to the other, if they were touching in a way that some were sloughed off.

DNA has been shown to transfer from a person’s hand to a child’s toy and then onto a lab coat12.
This I have a hard time believing. DNA wouldn't been on a person's hand. to get to the lab coat.

Now in a lab, where DNA has already been extracted; the problem of transfer and contamination is much more of a problem. And yes, sometimes samples can be contaminated from samples that were on a bench a day before. Often it is not known exactly what happens. You would not visually see tiny amounts, a small number of cells can be left on a surface and one would not know. But it would be direct transfer. As you say, DNA gets on a glove and gets into another sample. A pipette tip is not changed and used in the sample and evidence (although this should never happen as the 2 should not be out in the same room at the same time). The technician directly gets his/her DNA in the sample.

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