How does inheritance of blood types work?
There are three blood genes: A, B, and O. (I’m going to ignore the + and - part of this.) A and B are dominant, and O is recessive. You inherit one blood gene from your mother and one from your father. The combination of genes determines your blood type. There are four possibilities: A, B, AB, and O. Here’s how it works:
A + A = A
A + O = A
A + B = AB
B + B = B
B + O = B
O + O = O
The Rh (Rhesus) blood group system (including the Rh factor) is one of the currently 30 human blood group systems. It is clinically the most important blood group system after ABO. The Rh blood group system currently consists of 50 defined blood-group antigens, among which the 5 antigens D, C, c, E, and e are the most important ones. The commonly-used terms Rh factor, Rh positive and Rh negative refer to the D antigen only.
An individual either has, or does not have, the “Rhesus factor” on the surface of their red blood cells. This term strictly refers only to the most immunogenic D antigen of the Rh blood group system, or the Rh- blood group system. The status is usually indicated by Rh positive (Rh+, does have the D antigen) or Rh negative (Rh-, does not have the D antigen) suffix to the ABO blood type.