You have A neg blood your son has O what type must the mother have?

Since the son has O blood type, he must have inherited an O allele from his mother. The father has A neg blood type, which means he has one A allele and one O allele. In order for the son to have inherited the O allele, the mother must also have at least one O allele. Therefore, the mother must be either OO or AO blood type.