The LA times reports:

DNA "matches" are not always what they appear to be. Although a person's genetic makeup is unique, his genetic profile -- just a tiny sliver of the full genome -- may not be. Siblings often share genetic markers at several locations, and even unrelated people can share some by coincidence.

No one knows precisely how rare DNA profiles are. The odds presented in court are the FBI's best estimates.


For the whole article skip to:
http://www.latimes.com/news/local/la-me-dna20-2008jul20,0,5133446.story

JAS

Newspapers always speak the truth, don't they? But I guess we ought to be aware of the new assault on the reliability of DNA testing.

JAS

Not reading the article, but just your caption, I thought much the same thing.

It's all very Post-Witness-For-The-Truth.

[This message was edited by R.J. MacReady on 07-22-08 at .]

Well that just makes sense. This is a an oversimplification but suppose you examined a book and recorded the first letter of the 1st word, 10th word, and 100th word... and then keep going and get the first letters from word 1000, 2000, 3000 and every thousand up to 10000 so you have 13 data points like the DNA profile in the linked article.

Now you would have a "book profile" and it would be a really good way to distinguish one book from another but every great once in a while you'd get a profile match that wasn't really the actual same book.

They shouldn't hide the data, especially if someone else is willing to pay for the statistical analysis... to protect privacy just turn over the DNA profile sequences and not the names.

If it turns out that their standard 13 data points arn't enough to support the promised odds of an accidental match then they should either pick some different spots in the genome where the DNA is more random or simply add more data points to the test. Convicting the wrong person means that there is a bad guy out there who got away with it.

quote:

---

Convicting the wrong person means that there is a bad guy out there who got away with it.

---

When it comes to DNA, there ain't no doubt my friend. Don't believe everything a Californian defense attorney tells you. You know we never landed on the moon and there are alot of books, articles, and witnesses out there that will support that position too!

So if DNA is not reliable we should stop all the exonerations of allegedly innocent prisoners who were wrongly convicted - and can we put all the exonerationed prisoners back in prison. Who would have thought that a defense attorney would work for the exclusion of DNA evidence and go against the innocence project.

Don't you enjoy the irony of it all?

JAS

but the reasoning is faulty. DNA has always been foolproof in excluding a suspect as the donor, because one person cannot have two different DNA profiles. The question is whether two people can have the same profile.

So assuming the exoneration cases involve examples of crime scene DNA being different from the defendant's, then those are reliable. The article is suggesting that a DNA match may not necessarily be conclusive, because the defendant may have the same DNA profile as the "real" culprit.

I however, have no reason to question the statistical analysis that these DNA profiles are subjected to before a "match" is announces. If the odds against the defendant being the wrong guy are 45 quadrillion to 1, the I think we've proved our case. I've never even heard a defense lawyer argue that "beyond a reasonable doubt" means better than 99% certainty. 99.99999999992% should be good enough.

quote:

---

Originally posted by WHM:
DNA has always been foolproof in _excluding_ a suspect as the donor, because one person cannot have two different DNA profiles.

---

Actually, this isn't right. A person can have more than one STR DNA profile--they are called chimeras. This can happen due to the presence of a fraternal twin in utero or due to medical procedures such as a bone marrow transplant.

Mitochondrial DNA also can be different in different places in the body, although that event should be detected during the analysis.

There are many other considerations regarding whether DNA evidence is inculpatory, exculpatory, or even meaningless. The "Arizona search" controversy deals at most with the accuracy of the probabilities generated by the lab.

And if you talk about chimeras in court, those jurors who are faith CSI: Las Vegas viewers will know all about it since the show did an episode a few years ago about a chimera and the different DNA results depending on whether they took blood or saliva.

Janette A

What is "DNA" anyway?? I think it stands for, "Did Not Attack".

Yeah, I saw that CSI episode, too. I even thought about including it in my response. But that is the exception that proves the rule.

Wasn't that the disease that Tom Cruise eliminated in one of the Mission Impossible movies?

JAS

I think so. I remember the antidote was Bellerophon.