I know how to get my DNA from a saliva sample, but what I’m wondering if it is possible to do this while leaving the DNA-less saliva sample uncontaminated, or at least separating the contaminants from the saliva sample after the DNA is separated.
In other words, what’s the easiest way to get a clean and DNA-free saliva sample?
Thanks!
it would probably be easier to make it then to take out the DNA
There’s DNA in saliva because there are cells there, particularly cells shed from the cheek and gums. You can remove all of the cells from the rest of the saliva. Otherwise, though, I don’t think it’s possible. All the methods of DNA extraction that I’m aware of will destroy the sample. I could be wrong though…
Need answer fast?
Why not just use water for whatever you need this DNA-less saliva sample for?
IANAScientist, but how about centrifuging it? Seems to me that will get all the cells containing the DNA separated from all the extracellular liquid.
Thats how it’s done with blood. Centrifuge the blood and separate out the red blood cells.
I’m trying to think of an easy way to get a DNA-free biological sample.
Last year, scientists showed that it’s possible to fabricate DNA evidence in blood and saliva. For blood, they centrifuged the rbcs out, extracted and amplified DNA from another source, and then put that DNA in the DNA-free rbc sample. It tricked labs into thinking the blood came from elsewhere.
I’m trying to determine if there is an easy way to do this at home and for cheap using stuff that anyone can acquire, since the ramifications of that would be fairly significant for criminal proceedings.
I personally can’t think of any way offhand of doing it, or at least any way that offers a reasonable expectation of success. I guess you could just treat it with a shitload of DNAse…
Thanks.
Any other thoughts on how to get a DNA-free biological sample? Saliva or otherwise.
You really need to think of what you’re asking here. You’re wanting to take a very complex sample, containing thousands of different compounds, and somehow selectively remove one of those compounds while leaving all of the others intact. The technology just simply isn’t there to do that.
The steps involved in DNA extraction are like whacking away at a huge block of stone with a sledgehammer to get at the diamond in the middle. You’re wanting to instead take a tiny drill, get the diamond out, and leave everything else alone. We just can’t really do that yet. It’s a big technological leap to go from the sledgehammer to the tiny drill.
The only thing I can think of to offer is to get a biological sample that doesn’t have DNA to begin with, like red blood cells (although you’d still have mitochondrial DNA, if you care about that) or follicle-less hair.
This would be much easier if there were some sort of context as to what this sample is for or why it’s needed.
Maybe I don’t understand the issue but why didn’t the scientists just use someone else’s blood? And why can’t you just use someone else’s saliva.
What is the point of removing the DNA to make a DNA free liquid and then replacing it with someone else’s DNA when you could just use their DNA and liquid to begin with?
I explained a few posts above (8:16 AM).
That makes sense w/r/t the saliva. I was trying to come up with an easier way than RBCs.
http://www.nytimes.com/2009/08/18/science/18dna.html
That article lists RBCs and salivas as two types of DNA evidence that can be fabricated, but only lists how it was done with RBCs.
I’m attempting to prove (or disprove) the idea that any Joe Schmo with enough of a desire can fabricate DNA evidence. If I can manage to do it with little to no money and little to know scientific knowledge, it would have significant ramifications in the legal world.
My first thought was to simply attempt to take the saliva of two different people, extract the DNA, and then swap the DNA and now the samples look like they came from the opposite person they actually came from. This is why I wanted a clean, DNA-free saliva sample.
Blood is the easiest way to do it technically, but also requires pricey equipment and/or social engineering, which leave a trail (and thus, someone could prove that the DNA evidence was fabricated, and it wouldn’t really be as groundbreaking).
As the article points out, one could just plant the framee’s cup or hair at the scene, but something like saliva on the victim or blood on the murder weapon would be a lot more convincing.
As I mentioned above, you could probably do that, but how are you going to get someone else’s blood without leaving a trail of “uh, he stole my blood?”
Let’s say I didn’t care who I framed, I just wanted to get away with a rape or a murder.
I take my own blood, extract the RBCs, and take the DNA from some random strand of hair I find lying around on the street or in a discarded hairbrush, combine them and splatter that on the victim or murder weapon or at the scene.
Or what if I do the same with semen?
Bodily fluid evidence is a lot more persuasive than someone planting a discarded cup at the scene.
http://www.fsigenetics.com/article/S1872-4973(09)00099-4/abstract
So many convictions/exonerations are based almost entirely on DNA evidence (blood, semen, saliva on the victim or some key piece of evidence). If it can be easily faked…that’s bad.
Am I the only one who thinks the OP is
[Severus Snape]
… Up to something.
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Did the experiments you mentioned use DNA from hair to fake the blood DNA test?
It still sounds like it would be easier to obtain someone else’s actual fluid samples (from a blood bank, sperm bank, etc) than to do these intricate laboratory procedures.
Well, that’s what I’m trying to find out.
I’m trying to see if its possible to pull this trick off with $0 and no specialized equipment outside of something you can buy for cheap OTC.
And yes, the experiments used DNA from hair, IIRC.
I don’t see it happening, for a variety of reasons.
At the very least, someone wanting to plant DNA is going to need training and equipment for PCR, which is not trivial. This person would presumably do their PCR in full manual style with a series of waterbaths, and this is as much an art as a science. If you do not have the skills to troubleshoot all the steps involved, you’re screwed.
The easiest way (I would think) to do what you want would be to simulate a saliva sample. You’d have to come up with some formula of chemicals that would have the same macro scale properties as real saliva. Then, you’d have to spike this simulated sample with your amplicon. Of course, your spiked, simulated sample must be able to survive subsequent extraction and amplification procedures, and must appear and react as normal samples do.
I think that, while perhaps possible, it would take a research team to be able to reliably and convincingly replicate saliva evidence. There are tons of technical details to get ‘just right’ so the forensic lab sees what they expect to see. Good luck.
Edit: Here is a link to one of the elementary ingredients required for PCR. I doubt that many people without specialized training can make a whole lot out of their description.
Not going to happen. This isn’t something you MacGuyver up with repurposed kitchen utensils. You need the appropriate equipment and background knowledge. It’s also very expensive. Biological reagents aren’t cheap. They’re even more expensive than equipment, even used stuff off of eBay.
That having been said, I was able to read the paper through my university’s databases and it has some interesting points. It’s not biased toward selling a product like I originally thought. The investigators applied bisulfite DNA sequencing procedures, which are already used to study DNA methylation patterns for epigenetic analysis, to be able to differentiate between synthetic DNA and organismal DNA. They also separate whole genome amplified counterfeits and counterfeits where only commonly used markers, like the CODIS system’s markers, are synthesized. I don’t see this screening being widely adopted anytime soon because it is time consuming due to the DNA sequencing requirement and the high barrier of entry for a would-be evidence fabricator. I see it being a fallback in cases where the defense can raise some actual doubt as to the authenticity of the evidence.
I can think of a way to jerry rig this up. Like others have said, spin down the cells (relatively low speed spin to avoid spinning down other components) would get rid of most of the DNA.
There would likely be some free DNA from dead cells in the sample that you would have to get rid of. There are magnetic beads that bind to DNA. Generally they are used for purifying out the DNA from a sample (you just run the beads bound to the DNA through a powerful magnet), but there isn’t any reason that you couldn’t take the flowthrough (lacking the beads and DNA) which would have the DNA depleted. The saliva probably wouldn’t be the ideal buffer for the beads to bind, but I would imagine that if you ran the samples with the beads several successive times you could get rid of the vast majority of DNA.
I’m not sure that there wouldn’t be signs that you had done this remaining in the sample though and not for $0.
Interesting. So what equipment would be required here? $0 was a bit of a hyperbole, but as someone who is pretty broke, I want to see if it can be done on a normal persons budget.
And thanks for the other responses guys.
Militenyi Biotec has a lot of magnetic separation equipment commercially. Basic setup would cost a few thousand dollars (my non-basic setup cost about 50K), and the kits to do the bead/DNA binding would probably run a thousand bucks or so. That said the magnetic separators are basically just powerful magnets, so if you were willing to sort of jerry rig something, you could set something up much cheaper. Not much choice on the DNA binding beads but to buy the commercial ones.