mutiple dna profiles

Debate and discussion of any biological questions not pertaining to a particular topic.

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Chris4
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Post by Chris4 » Tue Aug 09, 2005 4:39 pm

mithrilhack wrote:they tested his blood, not his semen...


But the semen in the woman was tested. So Dr Stein is correct (if her knowledge is correct).
It's always funny until someone gets hurt. Then it's just hilarious.

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canalon
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Re: DNA discussion

Post by canalon » Tue Aug 09, 2005 6:09 pm

alf wrote:My question to you is - Why would you automatically deem it logical, for any semen to be found in a female, to be foreign?


Humm... because semen can only be produced by men... Unless I got my human biology completely wrong. Or I have a huge gender problem :lol:
Anyway this was more a jke than anything else, since I would assume that typing a sample of the victim DNA along with the rest seems a logical step to rule out cross contamination (scraping of epithelial cells with the semen for example).

alf wrote:What you may not realize is, when I am investigating a crime, I am not only examining (...) I have to be ready, and able, to answer every possible question that is asked of me, by the Prosecutor, and defense lawyer(s).


I understand, and I apologize if this joke was inapropriate.

As Dr Stein stated the survival of semen in vagina is short, but I think that if you retrieve any DNA different from the victim it can safely be assumed that it comes from the semen (DNA usually survive longer than the cells and can be tested).
Now, when you compare DNA from semen found in one of the victim and DNA extracted from the suspect you have a discrepancy. From my understanding in DNA identification people are more concerned by false positives (2 people with the same profile..) than by false negatives (one person 2 profile) which would usually have been tested when the test was devised (again, talk with the lab performing the test, they should be able to give you this kind of data!).
Besides assuming that your suspect is not the rapist, the only reason I can think of to explain your discrepancy would be that he had had a bone marrow graft that between the crime and the sampling (I do not know of anything like testes grafting...), you could rule this out by sampling some epithelial cells for DNA testing (swab in the mouth). Even that seem unlikely to me.
The easiest solution would be to involve a second person as the rapist at least. Or as Dr Stein suggested, your suspect knows/witnessed the crime and is accusing himself of it for some reason.

Good luck with your investigation

Patrick

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Dr.Stein
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Post by Dr.Stein » Wed Aug 10, 2005 9:40 am

Beside examining semen, do you have another things from the suspect like hair, skin, blood, and somehing else? How's the result from laboratory identification?

Hey, if I am not mistaken, you did not mention yet about fingerprints. Do they match to fingerprints of the suspect? If no, this case is not that hard, I think. Semen and fingerprints do not match with the suspect's, means that the suspect is not the real one. Maybe he witnessed that crime, knows the guy who did it, but he wants to protect him for any reason. If yes, well, this case is complicated. Aww :(

I should admit that this is very interesting, totally a new knowledge for me, and also because I do not have a deadline to think about this so I have much time to discuss anything. But for Albert, he must finish this case as soon as possible. I will help you as long as I know the point or I will just screw you up . I do not want to be that way :)
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Chris4
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Post by Chris4 » Wed Aug 10, 2005 9:53 am

I can't believe this isn't common knowledge in the forensic science field. Haven't people been sentenced based on DNA evidence?

Or is that if there is a match then you have your killer, but if you don't have a match then he could still be your killer, due to multiple DNA profiles, but you need further evidence?
It's always funny until someone gets hurt. Then it's just hilarious.

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Post by Dr.Stein » Wed Aug 10, 2005 10:02 am

I think you don't read the whole story of the case yet...? :?
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Chris4
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Post by Chris4 » Wed Aug 10, 2005 10:42 am

Dr.Stein wrote:I think you don't read the whole story of the case yet...? :?


Fair enough. I read through it again and i understand a bit better now.

I'll leave the investigation to you.
Can you not just ask the FBI or someone? Surely they will know. This seems like something which should already have been investigated by the top scientists in the field.
It's always funny until someone gets hurt. Then it's just hilarious.

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