Can a man blood type B+ and a woman blood type O+ have a child with blood type A+?

Mom could be either AA or AO and have either +/+ or +/- Rh factor alleles. So she could give her baby either an A or O allele and either a + or - Rh factor allele.

Dad could be either BB or BO and will also have either +/+ or +/- Rh factor alleles, and could give his baby either a B or O allele and either a + or - Rh factor allele.

So the baby could be either:

* AB : getting A from mom and B from dad
* A (AO) : getting A from mom and O from dad
* B (BO) : getting O from mom and B from dad
* O (OO) : getting O from mom and O from dad

And his Rh factor could be either + or -, depending on which Rh factor allele he inherits from each parent. So this baby could have any of the possible blood types.

With newer DNA testing, using blood types to determine paternity, or who the father is, isn't really that useful anymore. The main problem is that this method just tells you what the blood type the father could or could not have, and since many of these blood types are common, it doesn't necessarily help narrow down who the father could be.

Still, it sometimes does come up when a baby's blood type isn't what the parents expect it to be.

I don't think it can happen.

The mother can only be OO as it is recessive so any other blood antigen A or B would display its phenotype.

The 'father' can only be BO or BB, there is no way he can give the child an A allele unless he was AB and then he'd be AB not B.

ABO blood group system - Wikipedia, the free encyclopedia
Look at the table in the inheritance section

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Originally Posted by jchester

Can a man blood type B+ and a woman blood type O+ have a child with blood type A+?

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Yes, it can happen. The way this can happen is through the (epistatic) interaction a second gene. The second gene is termed "H" and is the hh antigen system. See wikipedia hh antigen system - Wikipedia, the free encyclopedia
This is commonly called the Bombay phenotype & is quite rare. The women would be hh at the H gene & carries the A allele (either heterozygous or homozygous) at the ABO locus