 So first we're going to start out and we're going to look at some terms. First here we're going to talk about genotype. Genotype is the genetic makeup of the system. So when we're talking about genes and alleles, that's what the genotype is, is what your genes code for. In contrast to that, the phenotype is our observable physical appearance or the characteristics you can see with your eyes. So hair color, eye color, skin color, those things can vary even from what the actual genotype shows to us. Specifically on skin color, your genotype may code for a very dark skin color or a very light skin color, but your exposure to outside environments such as the sun and other factors can change the skin color a little bit with various types of melanin. Moving on, codominance, this is when both alleles of the genotype contribute to the phenotype. So this is not often seen, but we do see this very commonly with the blood types. So you have two different blood types, the A blood type and the B blood type, but if they do come together, you can have AB, and if they are both absent, then you have O. Also along that line, another codominant trait is the alpha 1 antitrypsin disease, and that is obviously a lung and or liver disease, and we'll talk about that at another point in time. Variable expressivity, this is where two people have the same genotype, but different phenotypes. So an example of that is neurofibromatosis type 1, and what you'll see is varying severity of these diseases with people. Some may have small or large Caffe LA spots. They may or may not have any cutaneous neurofibromas, and that is just due to the very real expressivity of that disease. Moving on to incomplete penetrance, incomplete penetrance is where you have a genotype or with a mutation that doesn't show the phenotype, so the BRCA1 gene. So this codes for breast or ovarian cancer, just because an individual may have the BRCA1 gene present does not mean that they will develop breast or ovarian cancer, it does give an increased propensity towards that. So we don't automatically jump to removing the ovaries or removing the breast just because they have that gene, but that will give us the ability to monitor that for the potential for development later down the road. Pliotropy, this is where 1 gene contributes to multiple systems. We think of this as phenyl ketoneuria, and what you see is you get, with phenyl ketoneuria you have light skin, you get intellectual disability, sometimes they'll have a musty body odor, so they have 1 gene that codes for phenyl ketoneuria, and you see that in several systems of the body. Anticipation, this is where you see earlier onset of the disease in successive generations. So a mother has something like Huntington's disease, her daughter, if she passes that gene to her daughter, her daughter will likely begin showing symptoms of Huntington's disease at an earlier age. Mosaicism is where cells within the same person have a different genetic makeup. This is due to some mutations that can either be happened after fertilization, or they can happen prior to fertilization in the individual egg or the individual sperm cell. If they're after fertilization, that's called somatic mosaicism. If they are in the egg or sperm cell, that's called gonadal mosaicism. Another term, locust heterogeneity, this is where you have a similar phenotype for mutations at a different loci. So these mutations occur at a different spot on a chromosome, but you see the same manifestations outwardly. Allelic heterogeneity, one example of the locust heterogeneity is albinism. A allelic heterogeneity is a similar phenotype from different mutations at the same locus. So an example here is going to be beta thalassemias. You can have a different coding mutation here, but it causes the same beta thalassemia.