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Thread: How reliable is DNA

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    SG Enthusiast horsemen_'s Avatar
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    How reliable is DNA

    this could open up a whole new can of worms.

    link



    State crime lab analyst Kathryn Troyer was running tests on Arizona's DNA database when she stumbled across two felons with remarkably similar genetic profiles.

    The men matched at nine of the 13 locations on chromosomes, or loci, commonly used to distinguish people.
    The FBI estimated the odds of unrelated people sharing those genetic markers to be as remote as 1 in 113 billion. But the mug shots of the two felons suggested that they were not related: One was black, the other white.

    In the years after her 2001 discovery, Troyer found dozens of similar matches -- each seeming to defy impossible odds.

    As word spread, these findings by a little-known lab worker raised questions about the accuracy of the FBI's DNA statistics and ignited a legal fight over whether the nation's genetic databases ought to be opened to wider scrutiny.

    The FBI laboratory, which administers the national DNA database system, tried to stop distribution of Troyer's results and began an aggressive behind-the-scenes campaign to block similar searches elsewhere, even those ordered by courts, a Times investigation found................................................
    more at the link

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    SG Enthusiast cybotron r_9's Avatar
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    Junior Member MadDoctor's Avatar
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    I think I read somewhere that a person can have two DNA patterns (lets say one pattern in his blood and a second in his sperm). I know... I saw it on CSI.
    People will forget what you said... and people will forget what you did... but people will never forget how you made them feel.

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    They had a documentery on PBS about it. Chimarism, one case they used was in a woman who was NOT a genetic match of her children. The second DNS sample was finaly found in her sex organs. She was on trial for welfare fraud when DNA tests were done on her and her children, she had gotten pregnant durring the trial. The mother and child were both tested right after the birth and were not a match.
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    resident Humboldt's Avatar
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    Quote Originally Posted by MadDoctor View Post
    I think I read somewhere that a person can have two DNA patterns (lets say one pattern in his blood and a second in his sperm). I know... I saw it on CSI.
    You just wanted to say sperm.

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    Elite Member ghost's Avatar
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    Quote Originally Posted by CiscoKid View Post
    They had a documentery on PBS about it. Chimarism, one case they used was in a woman who was NOT a genetic match of her children. The second DNS sample was finaly found in her sex organs. She was on trial for welfare fraud when DNA tests were done on her and her children, she had gotten pregnant durring the trial. The mother and child were both tested right after the birth and were not a match.
    I saw that too, it was an amazing, eye-opening story - and she wasn't the only chimera they discussed. Mind-blowing implications...

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    ♫♪ ♫♪ ♫♪ ♫♪ downhill's Avatar
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    I sent this thread to a good friend of mine who's an expert in the field. She mentioned that a lot of stuff in the article , has been refuted.

    Dunno why it doesn't get more press.


    Sidenote, for those interested in DNA sleuthing, there's a documentary on National Geographic, tomorrow night on Anastasia and the Romanov family. I've seen some of the data on it already and at least to me, it's pretty cool.

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    Hi. I’m the friend that downhill spoke of in his post above… and while I’m not sure I’d qualify as an expert in the field, I am definitely in the field and I have a pretty good understanding of the issues related to the Arizona search. I was at a conference recently where there was a good bit of discussion on the subject, and in talking to downhill today he reminded me of this thread… so I thought I would come and comment on a few things, in the hopes that my comments might shed a little light on the issues raised in the article in the original post.

    1) Regarding the thread title, the question that was raised as a result of the Arizona search was not “How reliable is DNA?”, but rather, “How reliable is a multi-locus match when a profile is searched against an offender database to find a ‘cold hit’?”

    2) cybotron has it correct that the number of multi-locus matches found in the database is largely a result of the pairwise comparison performed. In fact, the total number of profiles matching at 9 loci (122) exceeds the expected value (68.3) by only a factor of 1.8. A difference, to be sure, but not an enormous one. (To see those calculations, please see this commentary and analysis by Charles Brenner, a well-respected forensic mathematician: http://dna-view.com/ArizonaMatch.htm)

    3) The expected value for the number of matching profiles is based on an “idealized, simplified model.” That is, the equation doesn’t take into account the relatedness of any individuals with profiles in the database, nor does it take the possibility of population substructure into account.

    3) The majority of the 9+ loci matches that cannot be explained by the pairwise comparison are very likely the result of full siblings in the database (and in fact, I believe that the 11 and 12 loci matches were determined to be full siblings). While the total number of full siblings in the Arizona database cannot easily be assessed, simulations have shown that if roughly 3 – 9% of the database is composed of full siblings, it would explain the departure from the expected number of 9 and 10 loci matches.

    4) Population substructure also likely has an impact on the number of 9+ loci matches observed. And the potential for population substructure is exactly the reason that theta corrections are applied to Random Match Probability calculations.

    5) If the number of full siblings in the database and population substructure do not account for the entirety of the factor by which the observed matches exceed the expected matches in the Arizona database, the remaining (very small) discrepancy between those values may be the result non-matches that only appear to match due to a small number of “errors” in the database. What kind of errors? Most likely mis-typing at a locus, either as a result of laboratory or analysis errors, or non-concordance between different commercial STR kits.
    Last edited by bijou; 08-19-08 at 01:30 AM. Reason: mistyped a word; switched observed and expected in one place (I need an editor before I post stuff!)

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    ♫♪ ♫♪ ♫♪ ♫♪ downhill's Avatar
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    Welcome to Speedguide, bijou! That's one heck of a first post!

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    R.I.P. 2018-07-16 RoundEye's Avatar
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    Quote Originally Posted by bijou View Post
    ....Hi. I’m the friend that downhill spoke of in his post above…..
    WOW! ……. downhill does have a smart friend, that’s about as rare as a DNA match.

    Welcome aboard, watch out though………. don’t show MadDoc any pictures of your pets, Roody bites sometimes, and YardOfStuff is a wookie.
    Sliding down the banister of life ..........................

  11. #11
    ♫♪ ♫♪ ♫♪ ♫♪ downhill's Avatar
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    Quote Originally Posted by RoundEye View Post
    WOW! ……. downhill does have a smart friend, that’s about as rare as a DNA match.

    .

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