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Air is full of DNA

nature.com

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Re: Air is full of DNA

#61

Post by greazy »

azalemeth wrote: post #19

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 wou…

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.

Re: Air is full of DNA

#62

Post by greazy »

pfdietz wrote: post #53
throwaway27448 wrote: post #48

Earlier quoted context omitted.

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.

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. :)

Phylogenetics is amazing, given surviving members of a clade we can reconstruct the ancestors. Phylogeny techniques can use additional info, eg paleontological record.

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.

Re: Air is full of DNA

#63

Post by ksaj »

duped wrote: post #59
ksaj wrote: post #55

Earlier quoted context omitted.

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 mi…

> 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 ev…

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.

Re: Air is full of DNA

#64

Post by duped »

ksaj wrote: post #63
duped wrote: post #59

Earlier quoted context omitted.

> 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 ev…

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 m…

> it's literally a battle of what side can make the most compelling argument

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.

Re: Air is full of DNA

#65

Post by gus_massa »

cwmoore wrote: post #43
etiam wrote: post #38

Earlier quoted context omitted.

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?

No need to wonder if you study the lymphatic system.

> No need to wonder if you study the lymphatic system.

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.

Re: Air is full of DNA

#66

Post by butvacuum »

the__alchemist wrote: post #40
cmrx64 wrote: post #3

Earlier quoted context omitted.

four figures these days. fits in your hand. nanopore is a revolution. https://nanoporetech.com/products/sequence/minion 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 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…

not suprised. the website seemed to indicate to me (a layman in this area) that it expired based on time, not use- so Seqiencing As A Service (ha!) makes financial sense for most people.
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