Let's suppose we have an RH negative individual that is that has the blood group A, blood type A. What that means is they will have antigen A on their membrane and will not have antigen B. And it also means that because they don't have antigen B, their immune system will or readily produce antibodies against antigen B and those antibodies will circulate in the blood. Now, what it means for the individual to be RH negative is the following. They don't have that antigen D on their membrane, but their immune system will not necessarily produce the antibody against antigen D. The immune system will only begin producing that antibody against antigen D if they are actually exposed to that antigen D. And we'll see an example of this in just a moment when we discuss the process of pregnancy and childbirth. Now, it turns out that the gene that codes for the RH factor, the protein antigen D, is actually dominant to the recessive trait.