Any geneticists or biologists out there--blood type question

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Sooooo....I just discovered tonight that I have a different blood type than both my parents. I'm O+...neither of them are. I did some research, but not sure if I understand it correctly. They are not sure of their blood type, but they both know they are not O. If they are both A or both B or one is A and one is B, they CAN have an O baby, right? If one happens to be AB, then there is no hope for an O baby, and I belong to someone else?

I'll give this a shot, and the professional medical experts are welcome to correct me.

The human blood types are: OO, AO, BO, AA, BB, and AB.

OO is commonly referred to as simply "O".

AO and AA are commonly referred to as "A".

BO and BB are commonly referred to as "B".

AB is simply "AB".

There are 36 possible "matings" of blood types, each of which may split and recombine in the offspring to produce other blood types.

If the parents are OO and OO, all of their offspring will be OO.

If the parents are OO and AO, then ... it gets complicated ...

There is a 50% chance that each child will be type AO, or "A"
There is a 50% chance that each child will be type OO, or "O"

If the parents are OO and BO, then ...

There is a 50% chance that each child will be type BO, or "B"
There is a 50% chance that each child will be type OO, or "O"

If the parents are AO and BO, then ... it gets more complicated ...

There is a 25% chance that each child will be type AB
There is a 25% chance that each child will be type AO, or "A"
There is a 25% chance that each child will be type BO, or "B"
There is a 25% chance that each child will be type OO, or "O"

If the parents are AB and AB, then ... it gets still more complicated ...

There is a 25% chance that each child will be type AA or "A"
There is a 50% chance that each child will be type AB
There is a 25% chance that each child will be type BB, or "B"

...

As you can see, there is some matrixing involved, and any good phlebotomy text can give you a better explanation of how this works.

Or, you could try this neat Blood Type Calculator (link), and determine the answers for yourself!

little lily, ex-doc here. both you and fnord are correct.

This is correct. However, the important thing to note is that the Type O allele is recessive while the Types A and B alleles are dominant. This is why AO and BO are referred to as A and B, respectively. The dominant allele is what gets expressed.

In order for the recessive allele to be expressed, it cannot be paired with a dominant allele. This is why Type O blood requires receiving the Type O allele from both parents. However, it could be the recessive allele in each parent. For example, your mother could be AO and your father could be BO. Your mother would have Type A blood and your father would have Type B blood. If you inherited the recessive O allele from each parent, you would then have Type O blood.

As you said, if either parent has Type AB blood, it would be impossible to have a Type O offspring. If you want to read about an interesting application of this, look up the Charlie Chaplin paternity case. It's about this exact situation.

BTW, Fnord's percentages look correct to me, but it is easier to work out with a Punnett square.

I believe my mother is AB+ and my father is B or something, I am told I could have nearly any type. Apparently nobody has run a test on me yet. Might get some kind of home kit; I'm sure they exist.

AB + BB = AB or BB (50/50 chance)

AB + BO = AB, AO, BB, or BO (25% chance for each)

AB + "Something" = Anything except OO

What Fnord is saying is that the genes for both A and B are dominant, and that for O is recessive.

A and B are codominant to each other ( if you get one gene of each you get AB type blood).

If you are type O then you must be genetically OO ( homozygote), because a gene for either A or B would negate O and give you the other type.

But if either parent is A or B then they could be carrying the O gene ( could be homozygote or hetereozygote) If you are O then they both must be carrying the O gene and you got one copy of O from each.

The rest is what he said.