Now, by far the most common type of antigen within the RH facto group of the human body is known as antigen D. In fact, about 85% of the individuals living in the United States that came from Western Europe have a gene on their DNA that codes for the antigen D protein. So an individual with the gene on their DNA that codes for antigen D is known as an RH positive individual. And what this means is an RH positive individual will have the gene to create the antigen Z protein. So their red blood cells will contain that antigen D. On the other hand, an individual that is essentially RH negative does not have the gene on their DNA and so will not code and create that protein and will not have antigen D on the membrane of their red blood cells. So in this particular diagram, we're describing a person that is blood type A and which is RH negative. Now, unlike the Abo blood group, an RH negative individual will not normally produce the antibody against antigen D. However, if they are actually ever exposed to that antigen D, only then will their immune system begin producing the antibody against antigen D. And to see what we mean, let's once again look at the following diagram.