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Nope. ABO blood type, and Rh factor (the + and -) are coded for by different genes, so they are separate from one another. I'll talk about ABO first.
Type A and B are always dominant to (and will express over) type O. If you have two copies of the O gene, you'll be type O, but if you have an A and an O you'll be type A.
Type A and B are codominant, though. In other words, if you have one copy of the A gene, and one copy of the B gene, then your blood type will be type AB.
When reproduction occurs, the offspring gets one copy of each gene from its mother, and one copy from its father. We know what the blood types of the parents are, so we can narrow down their genotype and determine which genes they can pass on. The father's blood type is O. We know that O is recessive, so that means his genotype must be OO, and therefore he can only pass on an O gene to his child. The mother's blood type is A, which is dominant, meaning her genotype can be either AA or AO (we can't narrow it down without more information). That means she can potentially give an A or an O to her child.
Since the father can only give an O gene, and the mother can give an A or an O, when we figure out all the possible combinations, the child can either have AO or OO. That means the child can either have type A or type O blood.
The Rh factor is simpler, since it's straight Mendelian inheritance. The + denotes an Rh marker on the surface of the cells, and the - denotes the absence. This means that the Rh+ gene is dominant to the Rh- gene. We know both parents are Rh+. Since it's a dominant trait, that means that each of their genotypes could be either ++ or +-. That means that the child could inherit either a + or a - gene from each parent. When you do out all the possible combinations, you get ++, +-, and --. That means the child's blood type could be Rh+ or Rh-.
When you combine the ABO and the Rh factor, the possible combinations are A+, A-, O+, and O-.
This is the in-depth way. There's another way to figure it out. The B in type AB has to come from somewhere. Since B is dominant to O, and codominant to A, you'd always be able to see the presence of the B gene. If the mother had it, her type would be AB. If the father had it, his type would be O. Since neither parent has a copy of the B gene, then the child can't have one either. This quick method only works for type A and B, though - the O gene is recessive, so it can "hide" in either or both parents (as long as they're not type AB) and pop up unexpectedly.
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- thank you so much...