text: how do blood types combine? can someone with a+ blood type and someone with a- blood type, produce a child with b- type or o- type? two people with type a blood cannot produce a child with type b blood, but they can produce a child with type o blood.  in blood type, a and b are co-dominant, and o is recessive.  you inherit a gene from each of your parents, and they must both be o in order for you to have type o blood.  the same is not true with a and b.  those types show themselves if you only inherit one gene for either one.  in your example, both parents have type a blood.  the possible gene combinations (or genotypes) to produce type a blood are aa and ao.  if two people who are both ao have a child, and both parents donate the o to their offspring, the offspring will have type o blood.  when it comes to rh factor (the + and -), + is dominant, and - is recessive.  an a+ and a- couple can produce an o- child if the a+ parent carries the - gene.  one thing to note is that if we're talking about a real life example, be very concerned about the rh factor of the mother and the child.  if the mother has a different rh factor from the child, there could be serious problems with the pregnancy.  i hope that was not overly complicated for you.