silverfox
Posts: 1029
Joined: Thu Mar 15, 2001 8:39 am

DNA Question

Fri Jan 09, 2004 8:14 am

During lunch today, a chap came up with the following

1) DNA is unique to each person...

no arguments there

2) when somebody has a transplant. eg kidney heart lungs etc, he says they have to take drugs to stop the body rejecting the donor organ...

errr i think so, but not sure.

And, as a rider to that he said it is because the DNA wont change.. that i can see the logic of.


Now he threw the curved ball.


What then if a criminla has a blood transfusion, therefore gets blood with another DNA string, commits an offence, AND ( bear with us on this)the only microscopic spot of blood left at the scene was that of the donor blood.

What DNA would they find

His..... or the person that donated it?

And if it is the donors. AND there is a national database of all DNA (again bear with us, but it could happen, the way this world is heading). The wrong person gets done, especially if they havent got a 100% watertight alibi, like he was with the Pope or something

Any Med students out there that could put this one to bed for us?

Thanks
 
aa61hvy
Posts: 13021
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RE: DNA Question

Fri Jan 09, 2004 10:19 am

I'm pre-med and I'll try to answer your question.

I am almost positive the organ (from the donor) would not duplicate it's DNA, though I would imagine there would be 'stray' dna in the body of the recipient.

Did I answer your questions? If not, rephrase your question.
Go big or go home
 
redngold
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RE: DNA Question

Fri Jan 09, 2004 11:09 am

Here's an answer to your question:

1. Regarding DNA being unique to each person:
The only exception to this is identical twins Hower, the twins' fingerprints will be different because of minute environmental differences. This is how twins can be distinguished by criminologists.


2. In organ transplants, it's important for the recipient to take their anti-rejection drugs on a regular schedule. However, rejection can still occur, because the recipient's immune system cannot be completely suppressed.

The only organ that can be transplanted without concern over rejection is the cornea (part of the eye.) The cornea does not contain blood vessels and receives oxygen by diffusion from the air. If the cornea had blood flow, it would also be susceptible to rejection.


3. In blood transfusions, the blood is filtered for white blood cells to prevent a transfusion reaction. White blood cells are active in the immune system and would be too likely to cause a reaction even though the antigen and Rh types are a perfect match.

DNA is found in the nucleus of each cell, but with no white cells left in the blood, you only have platelets and red blood cells. Platelets are not full cells. Red Blood Cells happen to be the only cell in the human body that do not have a nucleus. Since RBC's don't have nuclei, they don't carry DNA.
Therefore, when a donor's blood mixes with a recipient's, there's no donor DNA in the person's bloodstream.

I wrote this information before I looked for a link. Turns out I'm exactly right!
see: http://www.madsci.org/posts/archives/feb2000/950993606.Bc.r.html

redngold

PS I'm a nursing student, formerly pre-med, and hematology (study of the blood) is one of my favorite subjects.
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aa61hvy
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RE: DNA Question

Fri Jan 09, 2004 11:17 am

Good call Red.. I'm still searching for my emphasis (either plastic surgery or OBGYN)
Go big or go home
 
AC320
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Joined: Fri Jan 05, 2001 11:29 pm

RE: DNA Question

Fri Jan 09, 2004 11:19 am

I decided my emphasis after some med prep work here at university; law school. Sue you guys in a few years...
fuddle duddle
 
aa61hvy
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RE: DNA Question

Fri Jan 09, 2004 11:21 am

Except a good doctor can get a better lawyer than you  Big grin
Go big or go home
 
redngold
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RE: DNA Question

Fri Jan 09, 2004 12:07 pm

AA61hvy: you're pre-med, so concentrate on finishing your coursework with good grades. Get some volunteer experience in a health care setting if at all possible. It will look good on your med school application. And don't forget some art classes -- something that will get you working with your hands. It will pay off in med school. Don't worry about your specialty -- you'll have plenty of time (and various rotations) in med school to figure out what you want.

AC -- you might try studying some bioethics... well, ethics in general, ( Big grin ) before you think about suing any of us medical professionals. (Just the usual dig at lawyers) Actually, biomedical ethics is a growing field -- as medical science becomes more a part of our daily life, you're going to find biomedical ethics weighing in on more and more legal actions.

****

Just to give a little more of my background, I was accepted to Boston Univ. School of Public Health out of college... with the option to apply to the medical school proper after I finished organic chem. I decided not to go, which was a tough decision because I knew I'd probably never get in again. I've worked as a librarian for several years now, but the hospitals keep calling... So I went back to school last year, and I'm slowly making my way through the prerequisites before I start the nursing classes proper. One step at a time (like I suggested, AA61hvy) but my ultimate goals are either 1) nursing anesthesia, or 2) patient advocacy.

I really love learning about the human body! It's incredible how we're designed...


redngold
Up, up and away!
 
AC320
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RE: DNA Question

Fri Jan 09, 2004 12:11 pm

Actually the funny thing is I have been considering that specialty, or some corporate/business practice. I do have a mind for medicine and sciences so it might be a good fit.
fuddle duddle
 
aa61hvy
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RE: DNA Question

Fri Jan 09, 2004 12:14 pm

Nursing anesthesia
90-110K...  Big grin At least in Texas

[Edited 2004-01-09 04:15:33]

[Edited 2004-01-09 04:16:28]
Go big or go home
 
AWspicious
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RE: DNA Question

Fri Jan 09, 2004 1:31 pm

"I really love learning about the human body! It's incredible how we're designed..."


redngold




Some of us more so than others...

Signed
BigPhilNYC


(Sorry, man. Couldn't resist)  Laugh out loud
Nevermind political correctness - Envision using your turn signals!
 
StarAC17
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RE: DNA Question

Fri Jan 09, 2004 2:17 pm

1. Regarding DNA being unique to each person:
The only exception to this is identical twins Hower, the twins' fingerprints will be different because of minute environmental differences. This is how twins can be distinguished by criminologists.


One interesting thing about identical twins is that they if they were to have sex with the same girl and she got knocked up it would never be known who was the father.
Engineers Rule The World!!!!!
 
aa61hvy
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Joined: Fri Nov 05, 1999 9:21 am

RE: DNA Question

Fri Jan 09, 2004 11:13 pm

So true StarAC. I was talking about this with my girlfriend. She is an idenitical twin, so if her sister were to kill someone, my girlfriend could be accused of it.
Or if my girlfriend needs an organ or blood tranfusion she could always turn to her sister.. Must be nice!
Go big or go home
 
L-188
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RE: DNA Question

Fri Jan 09, 2004 11:16 pm

Do you guys remember hearing about that Canadian doctor who raped a drugged patient and then they couldn't match his DNA from a blood sample taken from the arm with a sample taken from the victim.

Turns out that he inserted a length of surgical tubing in his arm that he filled with somebody else's blood he got at the hospital. Then when they took the samples from his arm, they mistook that implanted tube with a vein.

Took a hair sample to prove that he was the rapist.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
N6376M
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RE: DNA Question

Sat Jan 10, 2004 1:43 am

A couple of points -

1. As for the blood. The RBC are being created and die every X number of days (I think it's around 46). Therefore, for some period, there would be some foreign DNA in the receipients body but it eventually would be flushed out. The odds on finding the neddle in the haystack is astronomical.

2. As for the bigger issue. The statement that no two people's DNA is exactly alike is correct. However, the entire DNA molecule is huge. When a lab tests DNA, it just compares segments of the entire molecule and not the whole strand. This is why DNA testing cannot definitely conclude that the DNA from two samples is a match. What it does do is give you a probablitity of 1 in a Billion or greater that the two samples came from the same person.

This fact is frequently used by defense attorneys to attack DNA results. Remember to OJ trial. The prosecution stated that their was a 1 in 4 billion chance that the DNA at the murder scene was not OJ's (this implies that about they could rule out everyone but about 5 people in the world from having the same DNA found). DNA can conclusively be used to say that two blood samples do not match with 100% certainty because if a specific segment of the DNA doesn't match, there is no need to examine the whole molecule.
 
redngold
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RE: DNA Question

Sat Jan 10, 2004 3:03 am

N6376m --

1. As I stated before, all mature red blood cells lack a nucleus. Since DNA is contained within the nucleus, there is no DNA in red blood cells. Therefore, there is no DNA transfer to the recipient, period. The only way DNA would be transferred is if the donor had a blood disease that caused immature red cells to be released into the bloodstream, and that blood would automatically be discarded through normal screening.

2. Identical twins do indeed have identical DNA (genotype.) It is environmental factors that create differences in their fingerprints (phenotype.)

Did you even read my post?
Up, up and away!
 
silverfox
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RE: DNA Question

Sat Jan 10, 2004 8:06 am

Gents

thanks for the informed and reasoned replies.

Looks like a good discussion when i get back to work after the op!


 
jimbobjoe
Posts: 450
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RE: DNA Question

Tue Jan 13, 2004 8:34 pm

A bit off topic (on a dead thread anyway) but I once came up with the idea of a DNA bomb. It's a device full of random DNA from, well, anything. Hair from multiple people, whatever.

In order to hide his/her tracks, the criminal puts it at the scene of the crime, lets it blow, and then a huge quantity of DNA material is spread around, making it difficult to figure out whose DNA is whose.

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