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DNA

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eggshaped
60061.  Wed Mar 15, 2006 12:24 pm Reply with quote

Scenario: There has been a murder, and a fresh blood stain at the scene of the crime has DNA which matches yours - what is your defence?

Answer: You have donated bone marrow to an evil killer.


Notes:
While DNA detection has a reputation of being foolproof and unbeatable, there is one way to beat the system - and it was shown up last year in a case in Alaska.

What if a criminal has a blood transplant with blood that you have donated, could you end up being implicated in the crime? Thankfully the answer is no, most blood transfusions are actually done with packed blood cells, containing no DNA in themselves, which help the body to transport oxygen around the body. That said, even with whole blood transfusions, studies have shown that the DNA of a donor does not show up in the body of a recipient, irrespective of the amount transferred.

However, complications arise when bone marrow is transplanted. When marrow is successfully transplanted, hemocytoblasts (the stem cells which create blood cells) begin to produce white blood cells and platelets which contain the the donorís DNA. Add that to the fact that the recipientís bone marrow is probably not working properly anyway, and you have an individual whose blood sample contains another personís DNA.

In a recent case in Alaska, this very situation occurred, after a sexual assault a perfect match was found, but it was discovered that the perfect match had a perfect alibi - he was in prison at the time. After careful detective work however it was realised that the jailed man had received bone marrow from one of the suspects (actually his brother) many years earlier and the culprit was found.

http://www.newscientist.com/article.ns?id=mg18825234.600
http://www.newscientist.com/article.ns?id=mg18324603.100

Jumpingjack's post on fingerprints, followed by Gray's response and my stats.

Also, see Frederick the Monk's post on Polygraphs

 
eggshaped
60065.  Wed Mar 15, 2006 12:32 pm Reply with quote

One of the first forms of a polygraph was from Ancient China. The accused would be fed a mouthful of dry rice; if he had the moisture in his mouth to swallow it, he was considered to be innocent.
http://www.polygraph.org/president.htm

 
eggshaped
60066.  Wed Mar 15, 2006 12:36 pm Reply with quote

How fingerprints are formed:

Quote:
Skin is made up of several layers, including the basal layer, which separates the outer epidermis and the inner dermis. Fingerprint development begins when the foetus is about ten weeks old and the basal layer begins to grow faster than either the epidermis or dermis in the tips of the finger. This leads to an increased stress in the basal layer, which causes it to buckle inwards, creating ridges on the surface of the skin.

 
Frederick The Monk
60072.  Wed Mar 15, 2006 12:43 pm Reply with quote

eggshaped wrote:
One of the first forms of a polygraph was from Ancient China. The accused would be fed a mouthful of dry rice; if he had the moisture in his mouth to swallow it, he was considered to be innocent.
http://www.polygraph.org/president.htm


A similar thing happened in Anglo-Saxon England where trial by ordeal was popular as it was beleived that God would indicate who was guilty. Whislt for ordinary folk this involved such nasty ordeals as trial by hot iron and hot water, for clerics you could be tried by stale bread. You had to eat the very dry meal without choking to prove your innocence.

 

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