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. And that's because both of these autosomes, both of these homologous chromosomes have a non functional gene that is given by lowercase D. And so they will not be able to produce that fully functional protein that is needed by the cell. So now that we know what we mean by an Autosole and recessive disease, let's quickly look at four individual examples. Now, we're not going to go into too much detail on each and every one of these diseases.