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Hi Fraser!
Thanks for your question! So, you want to know how it is possible for you to have O- blood when your biological parents have 0+ and B+ blood. First of all, I can tell you that it is certainly possible -- and explainable, through simple genetics.
A question very similar to yours was recently posted in the area of Genetics (February 16, 1999; I.D.#915921864.Ge; Subject: If the father has B+ blood type and the mother has O- can the child have O-). I strongly urge you to read the posted answer because it gives a nice explanation of some basic genetic terms that I will use in my explanation.
Generally, when we talk about blood types, we refer to two things. The letter refers to the ABO blood system and the plus or minus sign refers to a component of the Rhesus (or Rh) system. In the ABO blood system, a person can have one of four possible blood types: A, B, O, or AB. These blood types arise from a combination of three different alleles which I will refer to as A, B, and O. The A and B alleles are codominant, which means that a person with both of these alleles will express both the A and B phenotypes. In other words, a person with the A and B alleles will have type AB blood. On the other hand, the A and B alleles, while codominant relative to each other, are dominant to the O allele. For instance, a person with the alleles B and O will have type B blood. This information can be summarized as follows:
Genotype Blood type
OO O
AA or AO A
BB or BO B
AB AB
Applying this information to your question, we see that your mother must
have the genotype OO because she has type O blood. With type B blood, your
father may have the genotype BB or BO. But, since you have type O blood,
which can only arise from two O alleles, he must have one B and one O
allele.
Now, moving on to the Rh system… A person who has a plus sign in their blood is called "Rh-positive" and likewise, someone with a minus sign is "Rh-negative". In this context, there are two alleles, which I will call + and -. The + allele is dominant and the - allele is recessive. So, someone who is Rh-positive may have the genotype ++ or +-, while someone who is Rh-negative must be - - . This is summarized below:
Genotype Rh status
++ or +- Rh-positive
- - Rh-negative
Since you are Rh-negative, you must have two - alleles, one from your
mother and one from your father. Because both of your parents are
Rh-positive, this means that they both have the +- genotype.
I hope this information is helpful to you. If you would like further details on this topic, any basic biology or genetics text is likely to have information on the ABO and Rh blood groups.
-Nikki
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