In addition to the proteins (agglutinogens) existing on your red blood cells, other genes make proteins called agglutinins (a-GLOO-tin-ins) that circulate in your blood plasma. Agglutinins are responsible for ensuring that only the blood cells of your blood type exist in your body.
Older children and teens are unlikely to start calling a stepmom mom or mother partly because of their fear of disloyalty to their biological mom. It is vital for all parties involved -- biological parents and stepmom -- to support their child's choice of what to call the stepmom.
Despite being adopted by Sharon in mid-season 3, Rusty doesn't start calling her Mom until mid-season 4 as anything other than a joke. Similarly, members of Major Crimes and Gus say your mom when referring to Sharon Raydor and specify your biological mother when they mean Sharon Beck.