Re: how do you know if you have AA or AO genes

Hello,

I assume you are referring to the ABO blood type gene.

There are a couple of ways to figure this out.  The first one involves a bit of luck and 
knowing the blood type of your parents.  If your blood type is “A”, you know that you 
can either be “AA” or “AO”.  You got one of those letters (alleles) from your Mom, 
and the other from your Dad.  Depending on their blood type, you may be able to 
figure out if your genotype is AA or AO.  Let’s go through the possibilities:

If either one of your parents is type O, their genotype must be OO.  In that case, that 
parent must have donated an “O”.  So, if you are type “A”, you must be AO.

If either one of your parents is type “B”, and you are type “A”, that parent must be 
BO.  (If they were BB, then you would have to be type B or type AB).  In this case, 
you must be AO.

If both your parents are type “AB”, and you are type “A”, then you must be AA, since 
neither parent has an “O” to donate.

This leaves the possibility that both your parents are type “A”, or that one is type “A” 
and one is type “AB”.   In these cases, it is not possible to deduce your genotype 
based on the blood type of your parents.  The blood type of your children (if you 
have any!) may be informative.  For example, if you are type “A” and you have a 
child who is type “O” or type “B”, they must have gotten an “O” from you, so you 
must be AO.

The other approach is to isolate and sequence both of your copies of the ABO 
blood type gene, which would require a fair amount of time and effort from 
someone.  I am not aware of any simple blood test that can discern between AA 
and AO.

Alex