If the father is A positive and mother is O positive what would the child's blood group be?

There really is no saying what the blood group exactly is. But I would say the chance is probably 50% and 50%. But it depends on who's DNA is more dominate in your body. There really is no saying what the blood group exactly is. But I would say the chance is probably 50% and 50%. But it depends on who's DNA is more dominate in your body.

That depends completely on what recessive gene the father is carrying. We know the mother has only oo, because O is always recessive. Were she to be carrying a gene for any other blood type, she would not be type O because the other gene would be dominate. You carry two genes for the part of the blood type you're asking about. If Dad carries a recessive O, the children will be either type A or type O. If Dad carries a co-dominate A , the children will only be type A because all the genes the father can pass would be the dominate A. The only possibilities for Dad to have for a recessive gene is the co-dominate A or the recessive O.