Nafter

Aight, i was discussing DNA tests with some friends, and came accross this idea, If a burgler was robbing a house and cut himself on glass, the DNA of the blood was taken and a match found, normally this would incriminate that person. What happens if that person has had a blood transfusion on the days preciding, wouldnt he have others DNA, possibly several other peoples DNA in his blood? This could lead to a case of mistaken identity and the wrong person arrested?
How long do blood cells last in a persons blood, and is this hypothetical situation possible? or have we overlooked some key factor?

thoughts anyone?

Silvy

I'm no expert here but some thoughts come to mind:

- DNA testing is not 100% accurate even in the best of times. As evidence it is presented as a percentage based accuracy. So other evidence (even circumstantial is needed).

- Being arrested comes before DNA tests (usually) so they'd have to have a suspicion(sp?) first. If the test fails, they'd probably check some background anyway.

- To be convicted for a crime you not only would need to be at the scene but you would also not be somewhere else. iow: it's likely that the donor has a perfect alibi.
(never mind the fact that the donor could live thousands of miles away...)

- Don't the DNA tests show 'weird' results if the blood has been contaminated?
- Are tests done more than once to make sure?

In general: it's possible, but not likely in my opinion.

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lordjeebus

Blood cells last for about a month.

Assuming that a good quantity of the person's blood is not originally his, I would guess that the DNA test would come up as inconclusive.

Perhaps (I don't know how donated blood is tracked) the authorities could seek to find the source of his transfused blood, mix it with his, and compare that way.

More likely they wouldn't use the DNA as evidence.

The chances of accidently arresting the blood donor in the first place seem very low to me.

EDIT: Did some googling, they last about 4 months, not one.

krwlz

Also, most DNA tests out there simply eliminate suspects. Not nail it down to one person.

jay-g

If you think about it, the hosiptal where the suspect was born would know the blood type. Sooo.......

lordjeebus

That's irrelevant though. The suspect would have received a blood transfusion of the same blood type. Hospitals don't keep DNA samples of babies.

MSD

Transfusions would be of the same a/b/o type, but an rh+ person could recieve a sample of the same letter but rh-, or o-

I've asked this of a forensic scientist who visited our high school, and he said that either the transfused blood would not show up, or it would throw the results off enough that hair samples or a cheek scrape or similar tissue sample would be used.

Psivage

I always wondered about blood transfussion, I had a hell of lot of transfussion, through operations and such not. I keep thinking what is really me and what is really them. Does somebody's else blood change who you are. Ever since I was born I've had operation, so am I really me or somebody else.

lordjeebus

I doubt it. That blood doesn't stay with you forever -- it's eventually replaced by blood of your own. And blood cells can't differentiate into other types of cells, so the genes in them aren't going to do anything to you.

clavus

I guess you'd call the mistake a "Type-O."

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Reese

He would have different dna in him mixed with his and when they did the dna test they would find more than 1 persons dna. Since the DNA doesn't accuse someone unless they are already a suspect it's be near impossible for a donor to be found guilty.

Also, When they did find 10+ people's dna in the same drop of blood I would hope it would ring a bell that there's something fishy...

I'm not sayin it couldn't happen, but theres a better chance of winning the lottery 10 times in 10 days.

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dnd

i can't believe i'm actually laughing out load at that!!!

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txlovely

That was laugh out loud good... I can believe it. Simple humor - fast and slick. Gotta love it, Clavus.

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