1213 users online (248 members and 965 guests)  


Websleuths News


Page 1 of 3 1 2 3 LastLast
Results 1 to 15 of 32
  1. #1
    Join Date
    Aug 2003
    Posts
    1,058

    The DNA = Contamination.

    This is a good article that explains how DNA is processed in the lab. It also documents how easily crime scene samples can be contaminated and cause false readings. Here is a couple parts of the article which relate to the Ramsey case:

    "Generally, RFLP analysis requires larger amounts of DNA and the DNA must be undegraded. Crime-scene evidence that is old or that is present in small amounts is often unsuitable for RFLP testing. Warm moist conditions may accelerate DNA degradation rendering it unsuitable for RFLP in a relatively short period of time.

    PCR testing often requires less DNA than RFLP testing and the DNA may be partially degraded, more so than is the case with RFLP. However, PCR still has sample size and degradation limitations. PCR tests are extremely sensitive to contaminating DNA at the crime scene and within the test laboratory. During PCR, contaminants may be amplified up to a billion times their original concentration. Contamination can influence PCR results, particularly in the absence of proper handling techniques and proper controls for contamination.

    PCR copies DNA efficiently if the initial DNA is in good condition. A single DNA entity (molecule) can become millions or billions of DNA molecules in about three hours. In this way, PCR is similar to what happens when a clinical infection occurs. Clinicians have known for many years that a single germ (bacterial cell or virus) contaminating a wound can produce a massive infection if untreated. Similarly, a DNA molecule can contaminate (infect) a PCR and become a significant problem. The ability of small amounts of DNA to produce false and misleading results is well known within the research community.

    Prevention of false results involves the use of carefully applied controls and techniques. As described later, such controls and techniques can sometimes detect contamination but cannot guarantee that contamination hasn't influenced the results."


    http://www.scientific.org/tutorials/...ley/riley.html

  2. #2
    Join Date
    Aug 2003
    Posts
    1,795
    DNA Testing: An Introduction For Non-Scientists
    An Illustrated Explanation

    by DONALD E. RILEY, Ph.D.
    University of Washington
    (Copyright 1998)

    Interesting article. Anything more current?

  3. #3
    Join Date
    Aug 2003
    Posts
    1,058
    Quote Originally Posted by tipper
    Interesting article. Anything more current?
    Contamination doesn't come with an expiration date.
    And poor collection/handling procedures in 1996 will still be considered such well beyond 2004.

  4. #4
    Join Date
    Aug 2003
    Location
    The Wild West
    Posts
    1,911
    Quote Originally Posted by Shylock
    Contamination doesn't come with an expiration date.
    And poor collection/handling procedures in 1996 will still be considered such well beyond 2004.
    And DNA expert Kobilinksy cautions (in The Abrams Report interview about this case):

    LAWRENCE KOBILINSKY, PHD, DNA EXPERT: ...Now, I must say if they‘re using this special technology called low copy DNA, then it‘s a matter of interpretation. We have to be very careful because you can get some confusing results at times.

    http://msnbc.msn.com/id/3840387/

    Shylock, thank you for posting that article... very interesting.
    The intruder is innocent! JMO

  5. #5
    Join Date
    Aug 2003
    Posts
    1,795
    Quote Originally Posted by Shylock
    Contamination doesn't come with an expiration date.
    And poor collection/handling procedures in 1996 will still be considered such well beyond 2004.
    True but when you're talking about amplification techniques then the age of the article is relevant.

  6. #6
    Join Date
    Aug 2003
    Location
    The Wild West
    Posts
    1,911
    Quote Originally Posted by tipper
    True but when you're talking about amplification techniques then the age of the article is relevant.
    DNA expert Kobilinksy made his comment, above, just last week. So apparently there are still problems with the reliability of the technology.
    The intruder is innocent! JMO

  7. #7
    Join Date
    Aug 2003
    Posts
    2,199
    Shylock...thanks! That's good, sound information. It supports what an ABC online article (no longer available) said about PCR amplification. The article stated that according to CellMark, when the DNA being tested is old, degraded, or damaged, the imperfect DNA is amplified too. The imperfect DNA, or non-matching DNA, often produces extra markers (stutter bands, also called shadow bands) and gives a false impression that another person's DNA is mixed in with the sample.

  8. #8
    Join Date
    Aug 2003
    Location
    The South
    Posts
    61
    It appears from these posts about DNA that some DNA code not matching anyone on the planet may result from these tests.This sounds almost like a "checkmate" spin by the defense team.We now have DNA who's we will never know because he only exists in the laboratory.
    IN MY OPINION

  9. #9
    Join Date
    Aug 2003
    Posts
    1,058
    Quote: "Warm moist conditions may accelerate DNA degradation...in a relatively short period of time."

    Warm and moist, like in a person's crotch after they've urinated in their panties? (The autopsy documents that the panties are "urine stained".)

  10. #10
    Join Date
    Aug 2003
    Posts
    2,199
    Fulton...BINGO!

    A continuous no-match on the sample will give the Ramseys and Wood free rein to continue filing lawsuit after lawsuit, ad infinitum.


  11. #11
    Join Date
    Aug 2003
    Posts
    1,058
    Quote Originally Posted by tipper
    True but when you're talking about amplification techniques then the age of the article is relevant.
    Actually, "amplification techniques" are not even relevant to this case. They have always been able to amplify DNA by millions of times. The amplification of contamination is NOT a desired effect.

    What would be important to this case since that article was written would be recently developed "filtering techniques"--which would filter out contamination. But then, if you filter the contamination out of the DNA samples in this case, all that remains is Jonbenet's DNA. There is no second source, either under JonBenet's fingernails or in her panties, that is viable enough to amplify to a complete DNA profile.

  12. #12
    Join Date
    Aug 2003
    Posts
    3,053
    Quote Originally Posted by Ivy
    Fulton...BINGO!

    A continuous no-match on the sample will give the Ramseys and Wood free rein to continue filing lawsuit after lawsuit, ad infinitum.

    I don't think it's the DNA that's allowing the string of lawsuits involving Burke to be settled -- it's the fact, IMO, that Burke is protected by the court protective order that has been slapped on the case.

    The court will not allow any of these lawsuits to go to trial because it would involve discovery that would violate Colorado law protecting the privacy and identity of juvenile offenders. The New York Post went as far as it could and anyone could to prove Burke's involvement, but in the end had to settle. No court is allowed to violate another court's protective order.

    IMO the case was solved by the GJ and is over. I just hope no adult involved in the killing is walking.

    Just my opinion.

    BlueCrab

  13. #13
    Join Date
    Aug 2003
    Location
    maryland
    Posts
    1,832
    This information may apply to the original dna,however what is there to indicate
    these issues apply to the newest sample sent? Is it just conjecture on the part of
    those that really don't want there to be viable new evidence?
    ?IMO

  14. #14
    Join Date
    Aug 2003
    Posts
    2,199
    sissi, it's my understanding that the "newest sample" is merely an amplification of the original.

  15. #15
    Join Date
    Aug 2003
    Posts
    1,058
    Quote Originally Posted by sissi
    This information may apply to the original dna,however what is there to indicate these issues apply to the newest sample sent?
    This information applies to DNA TECHNOLOGY, past, present, and future. Crime scene contamination will be the same problem in the year 3000 as it was in 1996. (Probably worse, since the world isn't getting any cleaner...)

Page 1 of 3 1 2 3 LastLast