Can you trust your doctor?

This is not to knock medical professionals. It is rather to point out the conviction a professor, a doctor and a pharmacist can have while saying something that is 100 percent incorrect.
You cannot be an expert in everything. But if you have decision making power over things deciding whether or not your fetus will live, your baby will be born healthy or the father of your child believes that he is the father, then there are some issues and once again it hits home that everytime a medical professional tells you “nothing can be done”, it’s not time to despair … it’s time to get a second opinion!

Can a mother with blood type O (she is sure) and a father with blood type AB (he is not sure) have a son with AB blood type?

The answer is of course “yes” as both, the A and the B allele can be encoded into a single allele called cisAB where a person can be cisAB/O and coupled with the O mother produce either AB or O children.
A definitive answer such as

No. A and B are dominant allele, so, for a parent AB to have a child AB, he/she would need a partner with type A, B or AB. If the mother is sure that she is type O, she can only generate childs with types O, A and B, and never AB. That is how the genetic determination of ABO type is, the only way to break this rule would be the occurrence of a very rare event, such as mutation as someone cited here.

is harmful, no matter how you put it.

The following one examines the chimera aspect indicating clearly that this “genetics researcher” does not know about cisAB and the simplicity with which it works.

Yes, there is one way for this to happen and it is if the mother is a mosaic or chimera: DNA Double Take – NYTimes.com

Also here: Chimera (genetics)

Also search the case of Lydia Fairchild: Lydia Fairchild . In a paternity case, the children came up as definitely from the father but that they could not be biologically hers. At first people thought she had used the eggs of a donor but no, she had conceived naturally! The resolution was that she is carrying two genomes, one that gave rise to her eggs and one that gave rise to skin, hair and blood.

This is actually more common than it seems; what happens is that when there is a merger of multiple fertilized eggs and the result is one embryo where some tissues originate from one of the genomes, and others from the other. This also gives rise sometimes to people with differently colored eyes or two blood types.

But before you get too excited, consider the possibility that your parent’s blood types are being misremembered by one or both of them.

Of course, maybe you are adopted or maybe a donor egg was used. Or you were switched at the maternity ward.

Tell your parents what you’ve found out and see if they have an explanation or want to investigate further. Whatever the explanation is, they are still your parents. Parenthood is way more than biology.

The last part bolded is so accusatory and condescending, it appears to be the main resort of those who cannot take interest and time to inform themselves further before replying in a sly judgemental manner.

The physician/professor writes:

Only through immaculate misconception. There is no way a mother with type O blood can be the genetic parent of a child with AB blood type.

Great, a joke. And note the “no way” tone. And this is someone training the next generation of physicians.

Speaking of … a doctor in training expresses his confusion as follows:

Like others have said, a child of these parents would usually be either A or B.

However, mutations do happen, so that’s not always the case. It’s not even that rare, mutations happen all the time.

So I suggest that, if you wish to bring this up to your parents, you avoid making it sound as an accusation. Your assumptions could be wrong (you’re not even sure about your father’s blood type!). And even if you’re adopted, they are still your parents in all the ways that actually matter.

Good luck

So there you have it. Aside from my reply, a guy who “did some basic haematology training last millennium” states:

Yes, but only is the man is cis-AB or the woman is actually Bombay type hh.

Cis-AB allows transmission of both alleles as a linkage, whereas you’d normally only expect to see A or B being transmitted.

Bombay hh affects the accuracy of the test by changing the antigens and hence hides the real blood group i.e. the woman is actually A or B of AB but tests incorrectly as O.

Out of all the people he, the non-professional, is the one who knows about cisAB. The other part I was not aware of, but will look more into.

So two lessons:

1) An AB person CAN have an O child

2) If you ever hear your doctor say something is impossible, DO get a second opinion.
And if you are a medical student, it will not hurt to once in a while do your own digging when your professor tells you there is no need for it.

Your future patients are counting on you!