27 Oct 07
Where a single strand of DNA is reproduced thousands of times or more and then analyzed. I don't know how to directly link to this story on the BBC, but you can get to it from here:
http://news.bbc.co.uk/2/hi/science/nature/default.stm
The story is about in the middle down a bit, about the McCann case where DNA evidence is linking them to a crime, and also the worse bombing in Ireland's history, both cases pursued by a single strand of DNA. It also shows the thoroughness of BBC news versus what you would get about the story if you just went to Fox, or CNN in America. It is a full 15 minute report, well worth watching, a video report. Check it out and tell what you think.
27 Oct 07
Originally posted by sonhouseI hate watching videos 🙁. Is there a transcript somewhere?
Where a single strand of DNA is reproduced thousands of times or more and then analyzed. I don't know how to directly link to this story on the BBC, but you can get to it from here:
http://news.bbc.co.uk/2/hi/science/nature/default.stm
The story is about in the middle down a bit, about the McCann case where DNA evidence is linking them to a crime, and a ...[text shortened]... l 15 minute report, well worth watching, a video report. Check it out and tell what you think.
27 Oct 07
Originally posted by AThousandYoungI don't see a transcript, maybe if one would contact BBC online directly, the only thing I see there is a way to email a link to the video. It is well worth watching IMHO, however much you hate getting educated🙂
I hate watching videos 🙁. Is there a transcript somewhere?
27 Oct 07
Originally posted by sonhouseI love getting educated. I like to do it via the printed word.
I don't see a transcript, maybe if one would contact BBC online directly, the only thing I see there is a way to email a link to the video. It is well worth watching IMHO, however much you hate getting educated🙂
28 Oct 07
Originally posted by sonhouseI can't find the video you're talking about, but how could single strand DNA tests be a bad thing? You're probably referring to PCR, which is a method of replicating DNA from a tiny amount into quantities that one can do tests on, it basically is the genetic equivalent of a microscope, magnifying whatever is there to a quantity you can do real tests on.
Where a single strand of DNA is reproduced thousands of times or more and then analyzed. I don't know how to directly link to this story on the BBC, but you can get to it from here:
http://news.bbc.co.uk/2/hi/science/nature/default.stm
The story is about in the middle down a bit, about the McCann case where DNA evidence is linking them to a crime, and a ...[text shortened]... l 15 minute report, well worth watching, a video report. Check it out and tell what you think.
How that can be a bad thing, I don't know. If the DNA isn't there, it doesn't get replicated, naturally. I think the real problem you may have is the use of DNA evidence in the first place, though that's got nothing to do with the initial quantity found at a crime scene.
28 Oct 07
Originally posted by agrysonBoy, they buried that one, only one day after it first appeared. I did find it however, the problem is I don't see a way to post a link because there is no change in the URL, just a video window appears with the story. If you go to BBC science and nature, and to the video stories, put in DNA in the video search line and it comes up, titled, McCann Doubts about DNA.
I can't find the video you're talking about, but how could single strand DNA tests be a bad thing? You're probably referring to PCR, which is a method of replicating DNA from a tiny amount into quantities that one can do tests on, it basically is the genetic equivalent of a microscope, magnifying whatever is there to a quantity you can do real tests on.
Ho ...[text shortened]... place, though that's got nothing to do with the initial quantity found at a crime scene.
The gist is when DNA is amplified that way, the copies are not 100% perfect and small differences can show up from test to test so it is not as reliable as large sample DNA tests. They said it can be used ok as an investigative tool but should not be used in litigation.
28 Oct 07
1 edit
Originally posted by sonhousehttp://www.bbc.co.uk/mediaselector/check/player/nol/newsid_7060000/newsid_7063000?redirect=7063088.stm&news=1&bbwm=1&nbram=1&bbram=1&nbwm=1
Boy, they buried that one, only one day after it first appeared. I did find it however, the problem is I don't see a way to post a link because there is no change in the URL, just a video window appears with the story. If you go to BBC science and nature, and to the video stories, put in DNA in the video search line and it comes up, titled, McCann Doubts ab ...[text shortened]... sts. They said it can be used ok as an investigative tool but should not be used in litigation.
That's the url for the video (you can email a link to yourself from the site which doesn't change over time). From the video, the issue seems to be with a technique called "Low copy number" which I imagine from looking at how it was described is a form of PCR. I don't see a problem with using it as evidence in a case though given that we can measure the certainty with evidence of this kind much more easily than an eye-witness report for instance who may be mistaken on a car type or approximate height of a suspect for instance.
While it's important that in a legal context the uncertainties are made clear to juries, those uncertainties are measurable and what's more, forensic investigators by the nature of their job would be much more in tune with the more technical details of teh evidence, which cannot be reliably communicated to jury members. Evidence like this while not providing a solid case on its own can at least provide investigators with a helpful direction in their work for finding more reliable evidence.
I still can't see how this technique can be a bad thing, provided of course the professionals using it are fully aware of its pitfalls, which from several of the interviews in the video, they are.
Edit, for more infromation on PCR: http://en.wikipedia.org/wiki/PCR
No article could be found for Low copy number or any of its variants.
28 Oct 07
Originally posted by agrysonThe problem with low copy PCR, if it's what I think it is, is that a mistake or two in the first few cycles will screw up the entire batch.
http://www.bbc.co.uk/mediaselector/check/player/nol/newsid_7060000/newsid_7063000?redirect=7063088.stm&news=1&bbwm=1&nbram=1&bbram=1&nbwm=1
That's the url for the video (you can email a link to yourself from the site which doesn't change over time). From the video, the issue seems to be with a technique called "Low copy number" which I imagine from looki ...[text shortened]... ia.org/wiki/PCR
No article could be found for Low copy number or any of its variants.
28 Oct 07
Originally posted by AThousandYoungTrue, though even if there's a mistake in the first copy, you're still left with 50/50, and the chances of a mistake occuring in one of the interon sequences normally used in forensics is vanishingly small. Though it is a source of error that needs to be considered. Once again though, it's an error that can be statistically measured.
The problem with low copy PCR, if it's what I think it is, is that a mistake or two in the first few cycles will screw up the entire batch.