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.
it means that you share either a mom or a dad. Like if you have a half brother it means that you either have the same mom or you have the same dad. If you are step brother or sister it means that either your mom or dad married someone else with a child that is now your step brother or sister so you two aren't related at all through any parents.