Which cells to pick to get a pure sample of DNA without precise equipment?;Padosdigia.gw
Normally when conducting DNA testing, I presume techniques are utilized to ensure you're just testing one individual's DNA from a sample, even if it is possible that sample was contaminated one way or another.
However, in a thing I'm writing, there's a character that is able to produce personalized medicine for another individual after ingesting a sample of that individual's DNA.
The catch is that they can't always have laboratory equipment to isolate someone's cells (and thus DNA) from contaminants with other DNA (like from bacteria or just other people's dead skin). They might have to make due from eating hair or licking sweat, and so on, but the more contaminant DNA there is in the sample leads to reduced efficacy in the medicine.
My question, for the most part, would be which cells are good targets to collect samples from in this instance that are unlikely to have someone or something else's DNA in the sample; excluding anything that requires special equipment to get to or decontaminate the sample.
And to a lesser extent, which are the bad targets that fall under the conditions of being relatively easy to obtain a sample of, but are likely to have a high amount of contaminants?
-
$\\begingroup$ As this seems to be through ingestion, what DNA would be considered a contaminant? Would plant DNA interfere or DNA from animals (liked cooked food - though this would likely be fragmented)? $\\endgroup$ – JGreenwell 9 hours ago
-
$\\begingroup$ I would say any DNA not from the intended subject counts as a contaminant, animal or not. Though fragmented or otherwise damaged DNA would probably count as less of a contaminant than DNA from a living cell. $\\endgroup$ – Necrikus 8 hours ago
-
1$\\begingroup$ What level of technology do they have available. A bone marrow sample pre-industrial will kill the person faster than anything you are going to save them from. $\\endgroup$ – John 5 hours ago
-
$\\begingroup$ For the setting, slightly more advanced than current tech. However, this is for non-ideal situations (hence the lack of specialized equipment) so I'd say any current tech that is reasonable to carry around in case of emergencies. $\\endgroup$ – Necrikus 5 hours ago
-
$\\begingroup$ individual cells - it is not how it is done today, and no need to worry about that too much. contaminations can be sorted more on the side of reading DNA and stuff. use blood same as answers recommend, you need white blood cell for that as they have nuclei. Operating on individual cell level(sampling) with portable equipment is possible(needs microscope like device, which if we imagine a bit more advanced tech can be very small, for the task), but probably look for en.wikipedia.org/wiki/Lab-on-a-chip stuff. $\\endgroup$ – MolbOrg 4 hours ago
3 Answers
Rather quickly you are going to have to question where we draw the line between "your DNA" and "other DNA." It's clear on paper, but in practicality, its a hodgepodge mess. For example, viruses inject themselves into our DNA to replicate. Some have become permanent residents in our genetic code.
However, with all that side, blood would be a very powerful way of getting "pure" DNA. Our bodies have evolved to use bleeding as a way to clean out wounds, so it would be unlikely that blood taken from a carefully made would would be infected. A sterile knife is probably very useful for this, but that's a far cry from laboratory equipment. And given that our blood is full of nutrients and oxygen, we have a substantial interest in keeping foreign bodies out of it. Failure to do so often leads to sepsis.
-
$\\begingroup$ Since the question specifically asks "which cells", I would say "blood" is a misleading answer. Blood is mostly water and red blood cells; red blood cells in humans (like other mammals) do not have nuclei or mitochondria, and thus do not have DNA. There is DNA in white blood cells, but it takes a comparatively larger amount of blood to get a given amount of DNA compared to other tissues. Apparently quantity is less of a concern than purity, so I agree that blood is a good choice. $\\endgroup$ – brendan 30 mins ago
Brain or gonad cells would probably be the best, in terms of keeping bacteria and their DNA out. Both are well-protected from infection by necessity. The blood-brain barrier is only able to be penetrated by a few diseases, all of which show obviously neurological symptoms. If the person you want to sample seems healthy, their brain cells are very likely uncontaminated. Same thing with the gonads, both ovaries and testes. They're highly controlled because foreign DNA, like from a bacterium, can screw up gamete production.
One big problem with both of these is getting the sample without seriously hurting the person.
I think your next best bet is inside their teeth, especially if those teeth are healthy. Not much can get through enamel, and what does leaves obvious evidence; don't use rotten teeth. This is not as good, from a purity standpoint, as the brain however. Your teeth a pretty porous when they're forming, and will pick up foreign matter in your childhood. Scientists were able to find out where Otzi the Iceman grew up by examining pollen trapped in his teeth. I don't know how much pollen they found or how much your magic pharmacist can handle, but it's something to consider. On the plus side, anyone with a rock or other blunt object could knock out a tooth.
-
$\\begingroup$ I appreciate knowing that those are options, but I'm not entirely sure how one would obtain samples from those places without specialized equipment (or as you said, seriously injuring the subject). Granted, I can see obtaining a sample from the tooth by knocking it out with a blunt object or something, which doesn't count as "specialized equipment" but falls back on the seriously injuring thing. $\\endgroup$ – Necrikus 7 hours ago
-
$\\begingroup$ getting to the DNA in teeth will destroy the tooth, and mammals don't get any replacements. $\\endgroup$ – John 5 hours ago
You have to balance risk vs reward.
You have to balance contaminations risk with the damage you do obtaining the sample. A simple blood sample should work fine, minimum damage, low contamination risk, failing that a adipose tissue sample will lower the risk even more. Both can be obtained with a simple needle. Just sterilize wherever you put in the needle first, this reduces contamination risk but is also just a good practice overall.
Don't collect tissue from any part of the digestive tract or exterior of the body as they are covered in bacteria, the respiratory track also has a high contamination risk it is one of the main ways bacteria get into the body. Use basic common sense, the person has obvious infection then you need to worry about a more sterile source, and again you will have to balance the benefit of say a bone marrow source vs the risk of infecting the bone marrow. There is also the extreme pains collecting a bone marrow sample has, not something you should ignore.
