Air is full of DNA
nature.com
nature.com
"The chances of this person's unique DNA showing up at the scene are a zillion to one!"
"What does that really mean when the sample also contains unique DNA for a hundred other people? Did all of them commit the crime as a group?"
If the DNA is present, it's present - barring any procedural mistakes by the forensics technicians (mislabeled sample, dirty lab equipment, didn't follow manufacturers instructions, etc). Or deceit by one or more members of the forensics team to implicate the suspect.
This is the wrong point at which to correct the problem. When prosecutors are allowed to introduce "science" as their evidence, jurors give this way too much deference. It's the prosecutor basically saying "you're too stupid to understand it, so indulge my appeal to authority" and jurors tend to happily acquiesce. This is why judges are supposed to gatekeep expert testimony and not just let any quack step in and make outrageous claims... and despite their attempts, quacks have repeatedly done just that these past few decades.
If is true that the presence of DNA means essentially nothing, then it shouldn't be permitted to be introduced at trial. Protection from wrongful conviction shouldn't rest on someone having an attorney expensive enough to be able to unsway too-easily-swayed jurors with counter-specious arguments.
Air contamination is very unlikely. You aren't going to get air contamination inside the victim's bedroom... And if somehow a whiff of your air travelled a hundred miles into their bedroom and all over their corpse, other evidence would be used to rule you out.
This is why even breathalyzers have to be done twice, with a gap in between (and preferably with different sensors). It's also why several witnesses are examined. It's why fingerprints and lie detectors alone don't pass the muster. Nearly anything can be faked, or misinterpreted. All these things have to be used together to create an unbreakable story.
So there is next to no risk with DNA in the air.
As an example, there recently was a guy who went into a police station and claimed that he was relocating there from another province. The officer on duty was suspicious, and found there was no record of this officer in the entire country, and arrested him. In court, the guy got off the hook, even after impersonating a police officer and trying to infiltrate a station, because the officer on duty did not collect the appropriate evidence. The camera footage looked entirely normal. It became entirely hearsay.
You can pretty much expect him to charge that officer with wrongful arrest now.
We may never know what that guy was up to. But he certainly had chutzpah!
An uncharitable characterization is that forensics relies on many pieces of _stuff_ that cops and attorneys can reasonably convince a judge meets the rules of evidence and a jury that it is in fact evidence, while hoping the defense can't afford an expert (mind you, almost never a practitioner, but a professional legal consultant) to convince the jury it isn't evidence.
Most forensic analysis is complete bullshit, and it takes decades to convince judges to forbid the junk science.
So I wouldn't say there's "no risk." There's tons of risk.
What I would add is that you almost never have to worry about forensics if you're committing crimes, because the forensics are only going to be used to prove your guilt in court should you choose to fight it. If you're not committing crimes and become the focus of an investigation, you should be terrified of forensics.
Forensics isn't the way you characterized. There are forensic teams for both sides of every coin that needs forensics. It's literally a battle of what side can make the most compelling argument, and nothing more or less.
The most compelling argument is the one that has lots (the term "a preponderance" gets used in law where I am) of corroborating evidence through tools/techniques/people that are presumably not sharing and comparing notes or data with each other.
So it's exactly as I characterized it, a racket. It's not science.
Almost all forensic tests are bullshit, and forensic experts simply cannot determine what they say they are able to under any scrutiny.
Testing relies on amplifying many parts of the human DNA not just a small fragment.
The smaller the fragment the less precise the comparison.
So no, floating DNA does not meaningfully impact testing. It can impact PCR assays that target small regions for identification eg of viruses.
I'm always stunned when reminded that a full genome sequencing has gone from Human Genome Project's extreme cost and (edit: glacial) speed to using seqencing as the easy button.
I hear we've also got machines that'll seqence, fit on a bench, and cost high five/low six figures. They've got issues to work out still though- iirc something about damaged sections causing issues.
there’s youtubers that have videos about doing this in a home wetlab. very achievable. some amateur soil biologists using this to try and sample microdiversity as the planet… humanifies.
I use Plasmidsaurus instead: Pay them $15/sample online, drop off the tubes in a styrophoam box labeled with a dinosaur in a nearby university building; get the results next morning. They use Oxford Nanopore, but are loading your sample along with many other samples to maximize flow cell use.
I particularly like this Futurama clip on the subject. https://m.youtube.com/watch?v=VzGtk7Ip4NU
Not that I doubt that, but how does DNA help, when we have no DNA samples from dinosaurs?
But you're right, it is the fossil record that provides the strongest evidence.
Saying that birds have the same DNA as birds is not evidence of much of anything. :)
Eg here's a nice paper discussing Bayesian phylo combined with rexord sampling. https://www.cambridge.org/core/journals/paleobiology/article...
I'm in an adjacent field so take it with a grain of salt.
DNA is a molecule, not a microorganism or virus.
At this time of year, believe me, I am aware of the inhaled tree DNA setting off my pollen allergies.
One of the important steps in mRNA vaccines was to surround the mRNA with a lipid to ensure it can survive long enough to enter a cell. Naked mRNA would not have worked.
Sure, some samples will be off to antigen presentation, but does that inform more than this is an encountered foreign substance and this is how to bind to it for neutralization ? Seems like in principle you could take the overview picture and have something like olfaction, but for things that hadn't been sufficiently cracked open when they passed the olfactory epithelium. Maybe it's starting to be sorted out, but I'm not up to date on what the neural feedback from the immune system carries.
Does it mean yes or no? I think "no", but IANAMD; IANAB, ... I think it only identify proteins, glycoproteins, and other stuff that is in the surface of the cells/virus but not the DNA/RNA.
We can't make a certain HIV drug anymore because after 2 years, a lower energy crystal state formed, and that state isn't as effective. Now anytime we try to form synthesize the drug it finds a molecule of the lower energy crystal state which causes the crystal to also form in the lower energy state.
So the technology is indeed there to find the needle they're after in the haystack they're provided.
I think they had to delete all the sequencing data from the Wuhan Institute of Virology so stuff in the air wouldn't show up.
>Just as US institutes would claim that China is responsible, by the same token the argument works on any other lab too - yet the media did not present in that way. Ever. That's not accurate reporting; that's an attempt at victim blaming.