OK, here's blood grouping class,101.
We each have a lot of different blood groups. It's like, we also each have different characteristics for all sorts ofd things - we have eye colour, we have hair colour, we have skin colour, we have height and so on. A lot of these are not related to one another.
Each person gets two genes for each characteristic - one gene from the mother, one gene from the father. Where more than two possibilities exist (as in ABO) you can still only have two genes in your cells.
The ABO blood group system is an example of incomplete dominance with three alleles.
To simplify this - height is an example of complete dominance with two alleles, T (for tall) and t( for short). Someone who is short HAS to have typical teen. Someone who is tall could have either typical teen or typical teen (or typical teen - depending on whether they got the T from father, or mother). T is dominant, t is recessive.
So, back to ABO - A and B are incompletely dominant over each other. Instead of one taking charge, they are equally strong and both genes are expressed (ie each one produces a marker in the blood plasma). But O - it's recessive to both A and B.
My father was blood group O. My mother was blood group A. But since I KNOW I am blood group O, this means that my mother carried one gene for O and one gene for A. My father HAD to be OO (both genes are O).
husband is blood group B. From what we know, this means that either he's got BB, or he's got BO (I keep telling him!). Now since we know that at least one of our kids is O, this means that husband is carrying a B gene and an O gene.
Now, RH is different again. It's not related to ABO but we're often told our blood group as if it is. It's important to know your blood group because you can have some problems if you don't.
Some people can take just about any blood as long as it's either a match with the ABO system, or it contains a subset of what they have genetically. For example, while O is considered universal donor (ie O group can be given to anyone) those with O blood can only ever be given O blood. AB can only donate to other AB people, but they can receive blood from anybody.
Someone with A blood can receive either A or O.
But RH - it was found that in some rare cases, even matching the ABO group was not enough, a few rare people would be OK first time round but not the second. Or maybe the third. Most people - no worries. Then problems were noticed in babies with "haemolytic disease of the newborn". My grandmother lost all but her first two babies, to this mysterious condition until finally she was miscarrying earlier in each pregnancy and was told, "No more pregnancies."
Some time later is was discovered, using Rhesus monkeys, that some people's blood caused problems in the monkeys and some didn't. The Rh comes from Rhesus. Basically, some people's blood HAD the Rhesus factor (ie Rh+) and some didn't (Rh-).
If you give Rh+ blood to someone who is Rh-, it produced antibodies to Rh+ blood. Next time they get contact with Rh+ blood, it will be vigourously attacked. This can cause serious problems. If a woman is Rh- and is carrying an Rh+ baby, things should be fine unless the blood happens to accidentally mix - this often happens at birth but not before. That's why a woman who is Rh- should get an injection to stop antibody production, after each delivery or miscarriage.
My mother was Rh+. Her mother was Rh-. So we KNOW my mother had a gene for each - positive is dominant, here. I have a sister who is Rh- who had problems with childbirth. Lucky for me, I'm Rh+. So are all my kids, which makes me wonder if husband has Rh+Rh+ genes. Because of my sister, I know I have to be Rh+Rh-.
There are other blood groups further down the list but as these do not seem to produce antibody reactions that are a problem, they tend to be ignored.
With this knowledge you should be able to work out for yourself exactly how it works in your family. In your situation everywoman/katmom, I would be querying husband's results. Or failing that, easy child's.
If, after all your testing, you find that they have blood groups which make it clear that she couldn't be the biological daughter of both of you, I'd be looking into the chance the hospital switched her at birth.
This doesn't often happen. It is far more likely that some pathology technician has made a mistake. Or that husband's records are wrong.
Good luck, and your diplomas will be in the mail, after you complete a short quiz...
Marg