And this can also be either a upper case A or lowercase A. Now the second allele pair contains the B gene and likewise, we can either have uppercase B or lowercase B on each one of these individual chromosomes. And finally, we have allele pairs number three, homologous pair number three that contains the final gene, gene three or gene C that also controls and effects and has an additive effect on the skin color trait in humans. So we can also have uppercase C or lowercase C. Now, what do we mean by an uppercase C and a lowercase C? Well, notice that A, B and C are not complete dominance traits. In fact, they're incompletely dominant genes.