MadSci Network: Biochemistry

Re: can blood transfusions transfer dna so that persons involved in a crime

Date: Sat Feb 19 14:37:23 2000
Posted By: Mark Sullivan, Medical Student
Area of science: Biochemistry
ID: 950793337.Bc

Steve, What a great question! It's kind of like that man who had the hand transplant about a year ago. It never even occured to me that he is walking around with one set of someone elses fingerprints. But as far as blood transfusions confering the genetic identity of the donor to the recipient, it is not possible. Blood has three components, reb blood cells, white blood cells, and the fluid they are in called plasma. Simple blood transfusions deliver only red blood cells and plasma. The only job of a red blood cell is to delivery oxygen to all the tissues of the body. Transfusions are given to replace lost blood and plasma during surgery or some trauma so that the body can still deliver enough oxygen to the tissues. What is important about this is that red blood cells contain no nucleus, and therefore no individual genetic material. Why not give the white blood cells as well? White blood cells have too many cell surface proteins that would indentify them as "foreign" to our body, thereby causing the immune system to destroy them. Red blood cells contain only two types of cells surface markers, the A,B,O and Rh factors. When you get a transfusion, the doctors either give you the same blood type that you already have, or type O. Why type O? Well the short answer is that type O is the universal donor. This is because no one makes antibodies to the O cell surface receptor as everyone has this receptor. The AB type is the universal acceptor because people with this bloo type don't make antibodies to any of the blood groups. Rh factor works kind of the same way. I'll leave that up to you to investigate further. However, here is an interesting question for you. Would a bone marrow transplant confer the donor's gentic identity to the recipient? In that case the answer is yes! This is because in this case, the recipient's bone marrow is destroyed by radiation before the transplant. Then the donor's stem cells are given to the patient. Stem cells are the "primordial" cells of the bone marrow that produce all the blood cells, both white and red. Why doesn't the immune system do anything about this? Well that is because the immune system is the donor's so it doesn't see any thing foreing about the blood components. However the new immune system does recognize the recipient's tissue as foreign. This is why recipients are placed on immunosuppressants for the rest of their lives. But if this recipient did commit a crime where blood was left behind and skin or hair follicles, the blood DNA fingerprint would look different than the skin or hair DNA fingerprint. Isn't that wild? I hope this helps. Mark Sullivan

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