 Okay we're having an interesting weather through my window here so I'm getting sun and then it goes away and then I can't see and the lighting is going to be weird in this lecture but you know what that's just I'm not going to complain about sunshine coming through the redwoods. Okay let's talk about epistasis. The good news is epistasis our example is going to rely on blood typing which we just talked about. So epistasis is a phenomenon that happens when one gene overrides the expression of another gene and this I bet you can think of examples like albino critters. I want to say maybe I shouldn't give examples I bet you can think of analogies in your world where one thing the expression of one thing is dependent on the expression of something else. In our example with blood types we drew the red blood cell and then I don't know if you noticed but I drew a little dot and then I embedded the I can say it the antigen into the red blood cell at the dot. Well it just so happens that the dot is a protein that literally holds the antigen in the cell membrane and that protein which can write this down for you it holds the antigen in the cell membrane and it's called the H protein and maybe I will just highlight it for you so that you can see there those are the H proteins. Okay what happens like just go with me here take a wild take a wild guess what do you think happens if you don't make a functional H protein? So what if you have a genotype that leads to funky H protein? Well well let me tell you you're gonna have okay let's make the funky H I don't know how to draw a funky H oops can't make it that color I have to make it green those are funky H's and if you are looking at that and you're like dude how am I gonna plant an antigen in there? I make the antigen the body has the genes like this this person do you agree has type A blood and let's just say they have a IAA genotype so they have the genes to make type A blood but if they have the genotype that causes funky H then they have no way to embed those antigens in the red blood cell. I like to think of them those antigens now are just floating out there like they can't attach. What's my phenotype now? I would have expected that my phenotype is type A and definitely based on that genotype I would expect type A blood. Same genotype IAA but funky H and now we have what's my phenotype. Phenotype is what you look like what's my phenotype? Type O they have the genes to code for type A blood but they're missing a different gene that's necessary the H gene is epistatic to the I gene we should write that down to H gene is epistatic to the I gene the presence of H is necessary for the expression of I so you're gonna get a weird phenotype that doesn't match the expected genotype when you have epistatic interactions between genes do you think this happens yes it happens all the time and this is why I learned very early on biology instructors often like to do like weird problems that are like okay the baby's in the hospital and it got mixed up and who's its mom look at the look at the blood types and then you can tell well you might be able to tell but if you like there's complications and you might think like my parents are both A B why am I oh well it could be the H allele is missing the H gene is not expressed and therefore you do you did get the proper you got the eyes A's and I B's from your parental units but they also had funky H's they passed along to you that you are expressing so now you express type O blood okay how do you feel about that can you see how we're getting a little more complicated it's getting a little more complicated in here next up polygenic traits and pleotropy dun dun dun dun