How can a mother with a blood group AB+ and a father with a blood group of o+ have a son with a blood group of A-

No. It's not possible since both parents are Rh + the child will be positive also.

But I have done a blood group calculator and it said that my child could be either A+ B+ or A-B-

Again, using a punnet square, if both parents are positive, then the child has to be positive.

but i have done a blood group calculater and it said that my child could be either A+ B+ or A-B-

What about O? The father is O+ correct? Why did you leave O+ out of the calculations?

jem02081 disagrees: It is possible. 1/8 of the kids will be this phenotype A-

Please show me your references. Mine are medical texts that I used to get through nursing school.

How can a mother with a blood group AB+ and a father with a blood group of o+ have a son with a blood group of A-

J_9 is mistaken.

There are two separate traits here The AB blood group & the Rh blood group.
At the AB locus, Mom has an A and a B allele while Dad has 2 O alleles. So 1/2 of the children will be blood type A (phenotype)
A son who is Rh- must have inherited an Rh- allele from both of his parents, This means that both of his parents have an Rh- allele. They are said to be heterozygous for Rh (genotype). Their phenotype will Rh+

Make sense?

Please provide your references.

A reference for a dihybrid cross or my reference?

The reference you used to answer this question. AND, I digress, you are correct and my Nursing reference was incorrect. In doing more research, it is possible that the child in question here has either a positive or negative rhesus factor. While the negative factor is quite rare in this case, it is still a possibility.

Remember that your disagree to me stated that only 1/8 of the children will receive this factor, that leaves 7/8 that will be positive. So, while I was incorrect, the chances are slim, but still possible that this child is negative.

On this link from the University of Arizona, Biology Department, there is a blood type calculator in the lower left hand corner. When using that calculator, one can see that I was incorrect.

Blood Types Tutorial (http://www.biology.arizona.edu/Human_Bio/problem_sets/blood_types/inherited.html)

The reference you used to answer this question. I have a PhD and had taught genetics to undergraduates (including nursing students) at an American University for more than 10 years. You shouldn’t have to look this up. This is a simple "Mendelian dihybrid cross" (google it)

The question was
How can a mother with a blood group AB+ and a father with a blood group of o+ have a son with a blood group of A-
This question is asking if it is possible. The way to solve this question is first figure out the son’s genotype and then to work backwards to see if this can “fits” each parents’ genotype.

It’s a separate question to ask what is the likelihood (probability) of a specific outcome.
They are A+ = 3/8, B+ = 3/8, B- = 1/8 & A- = 1/8

Thank you for pointing this out. I have no problem admitting when I am wrong, and I was this time. :o

I also found this that is more in layman's terms for the OP to understand, again, it shows where I was totally incorrect.


Someone who is "Rh positive" or "Rh+" has at least one Rh+ allele, but could have two. Their genotype could be either Rh+/Rh+ or Rh+/Rh-. Someone who Rh- has a genotype of Rh-/Rh-.

A mother who is Rh- can only pass an Rh- allele to her son or daughter. A father who is Rh+ could pass either an Rh+ or Rh- allele to his son or daughter. This couple could have Rh+ children (Rh- from mother and Rh+ from father) or Rh- children (Rh- from mother and Rh- from father).

So, in this case, yes, the child can be negative.

Again, I apologize for my incorrect answer to this particular question.

Thanks for responding,
I hope to avoid hospitals, but when I'm in one I hope to run into a RN like you

Thanks for responding,
I hope to avoid hospitals, but when I'm in one I hope to run into a RN like you

Thank you very much for the compliment. I'm not perfect, I make mistakes, as we can see here (thank goodness for having a system in our hospital regarding 2 nurses double checking medication doses... :o )

After working 36 hours in a 72 hour period, sometimes my brain turns to mush and I rely on people like you jem, to correct me where I am wrong.

I work in the L&D department, and my reasoning for my answer (besides my incorrect text) is that when we have parents who both have positive alleles and the child is negative through a cord blood test, we automatically and systematically re-test the blood. In all my time as an L&D nurse (I have to update my profile as it is quite old now), I have yet to run into this particular situation. That is another reason I responded the way I did.

Thank you again for correcting the error I made previously.