Now, if the gene is dominant, we usually describe the gene with an uppercase letter. If the gene is recessive, we usually describe it with a lowercase letter. Now, what are the different possibilities of a female? Well, a female can be either homozygous dominant, and this is the case when we have, let's say, an uppercase B and an upper case B gene. So what's one example of a gene that is found on the X chromosome? Well, our gene that basically codes for color blindness.