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. So the gene that does not code for it. So to see what we mean by that, let's suppose we have a father that is heterozygous for that trait. So we have a dominant uppercase R and a recessive lowercase R. And let's suppose the father mates with a mother, a female that is also heterozygous for that same trait.