I do often wonder about stories like this in the context of forensic science – my (incomplete!) understanding a lot of the time suspect DNA samples are taken from small areas and amplified significantly with high-cycle count PCR. I'd worry that any jury presented with a statistical argument about a fragment of somebody's DNA being very unlikely ("1 in 100 million") to be different to the sample found at the scene would not be aware of all of the potential systematic reasons why the actual true probability may be much, much higher.
Terr_ 1 days ago [-]
Probability seems to be one of those things humans habitually mess-up at.
"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?"
chiph 23 hours ago [-]
Depends on how they're using it. To find an unknown person and prove they were at a scene - yeah you'll have the 100 person's worth of DNA to sort through and then match against a (presently) incomplete DNA database. But if you already have a suspect and need to place them at the scene, if their DNA is one of the 100 then they have shown that.
ch4s3 22 hours ago [-]
But we’re they at the scene or did they just bump into someone or something that was there?
chiph 22 hours ago [-]
That's something that would have to be addressed at the trial by the defense attorney raising challenges.
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.
XorNot 20 hours ago [-]
Except DNA may not be present: the probabilities involved with partial DNA matches become very problematic.
NoMoreNicksLeft 19 hours ago [-]
>That's something that would have to be addressed at the trial by the defense attorney raising challenges.
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.
ksaj 16 hours ago [-]
Forensics never relies on a single piece of evidence. It takes several corroborating accounts and pieces of evidence to reach "beyond reasonable doubt."
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!
duped 14 hours ago [-]
> Forensics never relies on a single piece of evidence
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.
ksaj 6 hours ago [-]
This isn't unlike "the right to remain silent." It's weird that people don't fully understand that to mean stfu for your own good, 'cos the only notes they are writing are toward building their case against you.
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.
greazy 12 hours ago [-]
Human DNA is relatively large. What's floating in the air is not going to be intact or complete.
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.
MagicMoonlight 21 hours ago [-]
Samples are normally things like your semen being found in the dead body or your blood on the broken window, or the victim's blood on your shoes.
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.
butvacuum 3 days ago [-]
buried the lede, imho: we have enough DNA profiles to match their sampling up with.
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.
robertlagrant 23 hours ago [-]
Ex-Nanopore employee here. One interesting thing we heard about internally was that OceanX[0] has one of our GridION[1] devices (slightly larger, and built-in compute) that they were using to track whales in the ocean by sequencing DNA found in seawater. Really cool.
I have a mol bio home lab, and decided against it because while the devices themselves are reasonably priced, the flow cells are an expensive disposable.
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.
dubi_steinkek 2 days ago [-]
Do you have links to these youtubers? Sounds interesting
samplatt 1 days ago [-]
Not OP, but The Thought Emporium is a personal favourite. Their name belies the hands-on nature of their videos.
Paleontology has been really helped by the ease of sequencing, to the point where many evolutionary arguments are moot. Humans are apes, birds are dinosaurs. Some people still dispute it, but not with evidence on their side.
Not that I doubt that, but how does DNA help, when we have no DNA samples from dinosaurs?
throwaway27448 20 hours ago [-]
Birds are dinosaurs because they are in the clade dinosauria. Their closest living quadrupedal relatives by genetic distance are indeed crocodiles.
But you're right, it is the fossil record that provides the strongest evidence.
pfdietz 18 hours ago [-]
I meant, "we have no DNA evidence from non-avian dinosaurs".
Saying that birds have the same DNA as birds is not evidence of much of anything. :)
greazy 11 hours ago [-]
Phylogenetics is amazing, given surviving members of a clade we can reconstruct the ancestors. Phylogeny techniques can use additional info, eg paleontological record.
I'm in an adjacent field so take it with a grain of salt.
throwaway27448 18 hours ago [-]
I think the genetic distance from crocodiles is still pretty strong evidence.
pfdietz 15 hours ago [-]
That just shows they diverged from crocodilians after that clade diverged from turtles. It doesn't show birds and dinosaurs are more closely related to each other than birds are to crocodilians (but the fossil evidence shows that.)
Should be noted, though, the cheaper/quicker techniques do still come with compromises compared to the "gold standard" technique used for the Human Genome Project.
dkobia 1 days ago [-]
This always blows my mind. We are currently breathing in the DNA of the trees, animals, and people around us—and we’re leaving ours behind for them, too. We’re all one big genetic soup.
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.
red75prime 24 hours ago [-]
"Soup" is a good word. Pieces of DNA resulting from destruction by nucleases and other enzymes.
SideburnsOfDoom 1 days ago [-]
> This always blows my mind. We are currently breathing in the DNA of the trees,
At this time of year, believe me, I am aware of the inhaled tree DNA setting off my pollen allergies.
gus_massa 23 hours ago [-]
The immune system destroy all the DNA in unexpected places in case it's a https://en.wikipedia.org/wiki/Viroid or something. Better safe than sorry.
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.
etiam 22 hours ago [-]
One has to wonder whether destroy is all it does though. Analyzing this as cues about the surroundings seems like it could be pretty useful for successful living, and something evolution could well pick up on.
Will we find eventually that some of those nucleic acid fragments were being hauled off for identification in something like an extra inner sense of smell?
cwmoore 21 hours ago [-]
No need to wonder if you study the lymphatic system.
etiam 20 hours ago [-]
Maybe so, but also maybe not quite my point, unless you know something I don't about it.
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.
SiempreViernes 15 hours ago [-]
If the quantities are too low for the nose to pick them up I think nature has converged on "too noisy to bother with".
etiam 14 hours ago [-]
Are the quantities too small though?
Really foul-smelling small molecules can be sensed at least down to ppb concentrations. And the recent technical use of "eDNA" demonstrates there's signal to be had.
throe939rjdor 22 hours ago [-]
Not just rna, but dna as well.
ksaj 16 hours ago [-]
People thinking how complicated this must be to filter through for forensics, forget that during and following the Covid lockdown, cities monitored sewage water for Covid viral load. They even recognized and reported the specific strains and their dominance in the samples. This includes finding "new" strains, and all this among all the other DNA/RNA bits to be found in city sewage.
So the technology is indeed there to find the needle they're after in the haystack they're provided.
nelox 1 days ago [-]
What a wonderful title, a breath of fresh air.
nasretdinov 1 days ago [-]
A breath of fresh _DNA_
seydor 1 days ago [-]
Let's wait for smartphones with nanopores
alansaber 22 hours ago [-]
Imagine the potential for targeted ads
madaxe_again 1 days ago [-]
I was chatting with a biologist friend a while back, and one tidbit he dropped in was that any sample of air from anywhere on earth will likely contain the dna of organisms unknown to science, so abundant the tree of life is.
adzm 21 hours ago [-]
Makes sense to focus on the pathogenic ones. There must be countless benign variations of life everywhere on a microscopic level
rcxdude 23 hours ago [-]
Yeah, there's just so many microorganisms (and some evolve so quickly) it would basically be impossible to really enumerate the species.
cwmoore 21 hours ago [-]
Sibling comments seem motivated to misreading parent here.
DNA is a molecule, not a microorganism or virus.
scotty79 1 days ago [-]
I firmly believe that there are thousands of times more species of viruses in circulation that influence human health, almost always in minor fashion, than we currently know. Any random, sub-clinical symptom is in my belief highly likely to be caused by one of such viruses.
dang 1 days ago [-]
[stub for offtopicness]
cwmoore 21 hours ago [-]
This is a fun-to-think-about variant HN comment thread, thanks Dan.
baxtr 1 days ago [-]
> Scratch your head and you’ll release DNA-rich cellular material into the air. There, it will mingle with DNA from myriad other sources: your own and others’ exhalations and exfoliations, fragments of hair, feathers, excrement, pollen and spores, and microorganisms such as viruses and microalgae. This DNA, which can include segments that are tens of thousands of base pairs long, will then wander the air for perhaps a few days, often clinging to dust particles. It can travel distances that range from a few metres to several thousand.
shevy-java 1 days ago [-]
[flagged]
dhruv3006 1 days ago [-]
Why is nature suddenly click bait - changing times I guess.
cmos 3 days ago [-]
As is the Ocean.
tim333 3 days ago [-]
Cool.
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.
shevy-java 1 days ago [-]
That was never a convincing argument, IMO. 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. Next thing someone may do is give a powerpoint presentation about weapons of mass destruction in some far-away country ...
philipallstar 1 days ago [-]
Actually, the US did a lot to downplay the idea that the nearby lab in Wuhan that was doing gain of function research on coronaviruses was in any way involved, to the extent that you'd get shadow-banned on Twitter for mentioning it.
popopo73 1 days ago [-]
>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.
So your idea of accurate reporting is to apply whataboutisms?
Rendered at 10:33:00 GMT+0000 (Coordinated Universal Time) with Vercel.
"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.
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.
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.
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.
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.
[0] https://en.wikipedia.org/wiki/OceanX
[1] https://nanoporetech.com/products/sequence/gridion
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.
https://www.youtube.com/watch?v=F0_q-fD_lyU
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.
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.
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.
So the technology is indeed there to find the needle they're after in the haystack they're provided.
DNA is a molecule, not a microorganism or virus.
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.