So to see what we mean, let's take a look at the following three diagrams. So we basically have an autosome on which both of these genes are fully functional and they're represented by uppercase DS. So this is homozygous dominant, and a homozygous dominant individual will have a normal phenotype, and they will not be a carrier for that particular disease. In the case of the heterozygous individual, because we have at least one of these alleles, at least one of these genes on one of the autosomal chromosomes is normal uppercase D. This individual will have a normal phenotype because they will be able to express that particular protein that is needed for that cell. Now, the other gene is abnormal, and that's why it's lowercase D, and that's why it is said to be a carrier of that disease. Now, this is the only genotype that will actually express the disease.