is blood type O not possible for an offspring whose mom has an AB blood type and the father has an A bloodtype?
It is possible for an offspring to have blood type O if the mother has AB blood type and the father has A blood type. Blood type is determined by the combination of genes from both parents. The ABO blood type system is determined by the presence or absence of certain antigens on the surface of red blood cells.
In this case, the mother having AB blood type means she has both A and B antigens on her red blood cells. The father having A blood type means he has only the A antigen on his red blood cells. Therefore, their child could inherit an A antigen from the father and a recessive O antigen from the mother, resulting in blood type O.
Blood type inheritance can be quite complex, so it is essential to consider the Rh factor as well to determine the complete blood type.