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Originally Posted by jennym
When that spot happens to be in the bathroom of college aged men? Very high odds. Should be easy to tell if the sample is a mixture of his DNA and her DNA, which would happen if it is her spit and his semen.
Again, the DNA should be a mixture.
That is one fucked up case.  |
When you say "SHOULD be a mixture" you fall into the common myth about DNA. You believe the test are perfect. It is far from that.
DNA test are about odds. In other words: "What are the odds that the material came from this person?". In a mixture the odds get worse.
Her saliva could be in a mixture but the test used cannot seperate a band of her DNA that is good enough to get a match.
Don't bet on DNA proving this case. When there is a DNA match it proves the case but when there is no DNA match it only proves that the test are not perfect.
Like I asked in another thread "If 3 Duke players jacked off in a cup could a DNA test of that cup identify all 3?".
I do know this much...if 1000 guys jacked of in that cup and it was stired up and sat for a day you'd probably only identify 3 to 5 guys if you were lucky.
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Originally Posted by http://www.dna.gov/training/letraining/glossary.htm
Exclusion - A DNA test result indicating that an individual is excluded as the source of the DNA evidence. In a criminal case, "exclusion" does not necessarily equate to "innocence."
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Originally Posted by http://www.dps.state.ia.us/DCI/Crime_Lab/DNA/index.shtml
What can be done with mixtures of DNA from two or more people?
This situation is commonly encountered with sexual assault evidence. DNA extraction procedures are used to separate sperm cell DNA from non-sperm cell DNA. In many cases this is successful and a clear profile of the perpetrator can be obtained. Sometimes complete separation cannot be obtained and the perpetrator's sperm cell DNA will be mixed with the victim's DNA. Blood-blood and semen-semen DNA mixtures can also occur. The ability to distinguish individual contributors to a mixed DNA profile will vary from case to case, and is highly dependent upon the relative quantity of DNA contributed to the mixture by each individual.
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Quote:
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Originally Posted by http://www.scientific.org/tutorials/articles/riley/riley.html
The (DNA) profile in this example could have come from a single person whose profile was, AB/AB/AC/AB/AB. Alternatively, two people of types AA/AB/AC/AA/BB and BB/AB/AA/BB/AA if mixed, could produce the profile. There are many other possible combinations of people who, when their DNAs are mixed, could produce the profile. In fact, the only individuals excluded are those possessing the HBGG, B allele and the GC, C allele assuming that the typing strip is reliably detecting all the alleles present. Extreme caution should be used when there is a possibility of a DNA mixture. It is arguable whether the system should be relied upon when there is an unresolved mixture.
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This last quote is the one that people should really try to understand.
What it is saying is that if
Person #1 (AA/AB/AC/AA/BB)
and
Person #2 (BB/AB/AA/BB/AA)
jack off in a cup(pussy) then the DNA test will
identify
Person #3 (AB/AB/AC/AB/AB) who may not actually exist.
Persons #1 and #2 CANNOT BE IDENTIFIED!!!!
However, they also cannot be excluded!!
Conclusion: The defense attorney will claim that his client DID NOT MATCH the DNA evidence, but he will convenietly not mentioned that his client was NOT excluded as a possible source of that DNA mixture.
Nifong is not as fucking stupid as some people think.