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Doctors' Answers to "Frequently Asked Questions" - Blood Type

These comments are made for the purpose of discussion and should NOT be used as recommendations for or against therapies or other treatments. An individual patient is always advised to consult their own physician.

Gene Testing for Blood Type [posted 1/8/99]
Question: My question is in regards to genetic testing and its validity in determining a person's blood relative. How can you tell if you are related to someone by gene testing? What are the factors involved that would invalidate the test results. For example, if person "x" was related to person "Y" by way of person "Y"'s mother who is related to person "x"'s father being a cousin to person "Y"'s mother. And person "Y" has a baby who claims the father is person "x". Can there be absolute evidence to state with out a doubt the father of the baby is his with this complicated situation. Now person "x" had no prior knowledge of the fact that he was related to person "Y" the mother of the baby.

Answer: The evidence is not absolute, merely predictive. That is, you can give the odds of the relationship, not absolute proof(unless a peculiar gene shows up).

Blood types
Question: How does it work when the mother has blood type A+, the father has father is B+, the son has O+, and the daughter has AB+?

Answer: Everyone has two different blood type markers with one each inherited from each parent. The most common are A, B, and O, although there are other markers, especially in other parts of the world. A and B are dominant, that is AO or AA is read as A , BO or BB is read as B and AB is read as AB. The only individuals who have O as a marker are OO . So , your mother is AO your father is BO. The son received one O from each and is OO, read as O. The daughter received A from mother, B from father and is AB. The plus marker is also dominant and each parent could be ++ or +- and the children could all be plus if they inherited one plus from either parent.

Blood type
Question: What are the different blood types? How are they determined? How are they know to be "givers" or "acceptors" of each types Can only A give to A, etc.)? What are the universal donors and acceptors?

Answer: There are three blood types. These are A, B, and O. In addition, there is an additional antigen which marks the cells as either positive(+) or negative(-). In general, one receivers one set of markers from each parent and O is not expressed. That is if one parent contributes and A and one parent O. The child will be Type A (actually AO). If one parent contributes A and the other parent B, the child will be AB. Positive is also dominant. That is if either parent contributes +, the child will be plus. So, each child can be either +, -(plus), - , +(plus) +, +(plus) or -, -(negative). Having an antigen will cause a reaction. So, Type A cannot receive B or AB, but can receive type O. Also, positive can receive negative without a reaction, but not the other way around. Therefore, O negative is the universal donor and can be transfused to any blood group. There is a rare type called O(h), Bombay which has A and B markers, but can't express the antigen due to an enzyme defect. These patients can only receive blood from another Bombay type-a, which is a very rare problem. Blood typing is very useful in paternity and identification testing. You can see that a child with O parents will only be O.

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