Expert: K Shows - 5/26/2006

Question

My wife and I are both blood type O , both of us had parents who had a parent with type O and one with type A blood.  So thats 2 type O and 2 type A grandparents.  

To add I am a twin whos blood type is A...so it is my contention that  I could father a child with my wife and the child could have either type A or type O blood.  my wife disagrees.

At 60 I don't plan on anymore kids..god forbid!
but would like to know who is correct on this differance of opinion.

thank j lombardi

Answer
Jan,

I am confused-- are you type O and your twin is type A?

If you and your wife are both type O then you can ONLY have kids with type O.  If you are A then you could have kids with type A or type O, depending on if you are heterozygous type A.

That is, ABO blood type is based on three types of genes: the A gene encodes type A antigen, the B gene encodes type B antigen, and the O or null gene encodes no antigen.  The antigen is a "sugar" that is attached to the outside of the red blood cell.  The A and B genes are codominant, meaning that either can be expressed and both can be expressed in someone having both genes; whereas, the O gene is recessive to both A and B genes, meaning that it is silent when in combination with either A or B.  So, someone who has type A blood can be homozygous (both genes the same) AA or heterozygous (both genes are different) AO.  Likewise, a person with type B blood can be homozygous BB or heterozygous BO.  A person with type AB blood can only be heterozygous AB.  A person with type O blood can only be homozygous OO.

So, for a person with type A blood (AA or AO) to have a child with type O blood (OO), they would have to be AO because the parent has to give one of the two genes of the child.  (If the parent was AA they would only contribute an A gene, which is dominant to O.)

I hope that this can settle your difference of opinion.