Re: Can parents with the blood types AB+ and B+ produce an O+ child?

Heidi!  No, this combination of types "cannot" produce an O+ child.  As you 
may know, both A & B genes are co-dominant and O is recessive to both A & 
B.  The types (A,B,AB & O) are the phenotypes or how the blood type 
exhibits itself.  These phenotypes are created by certain combinations of 
genes and these combinations are called a person's genotype.  For example, 
the phenotype O results from a genotype OO.  There has to be 2 genes since 
everyone inherits one gene from each parent.  That is why there is no truth 
in the belief that a child inherits the father, or the mother's blood type. 
 So, in order to be type O, both parents have to have an O gene to give to 
the child.  A parent with type A blood could have genotypes AA or AO.  The 
same thing for a parent with B type blood. That person's genotype could be 
BB or BO.  There is no way to determine the genotypes of people by testing. 
 The only way is by working backwards after they have had kids.  For 
example, if parents that were A & B types had a child with O blood type, we 
would know that both parents had an O gene to give to the child so they 
both were AO and BO genotypes.  So - if one parent is AB type they 
therefore have no O gene to give and therefore it is "impossible" to have 
an O type offspring.  I say impossible in quotes because spontaneous 
mutations are always possible but the chances of this happening are VERY, 
VERY rare.  For all practical purposes, the chances of it happening are 
close to zero!  The Rh factor (the + or-) is inherited like most traits 
so that 2 negative parents cannot have a positve child but 2 + parents 
can have a - child.  The genotypes would be Dd and Dd.  (D is the symbol 
used for this gene) The child would therefore be - if it inherited both 
dd genes.  If it had one or two D genes, it would be +.  If paternity is an 
issue, a full DNA match can be performed by a geneticist but a consult with 
a genetic counsellor would be cheaper and faster.  Thanks for the question 
& I hope my answer helps you.