 do think that the concepts in this lecture become more complicated as we roll. So this idea is tricky. Now we're going to talk about two genes that are impacting fruit fly phenotypes. And I've drawn the fruit fly, no I did not draw these. I stole the images of these fruit flies for you so that we can identify the different variants that we have possible to us. So linked genes are genes found on the same chromosome. Remember when we talked about Mendel? Oh boy Mendel we said you should go buy a lottery ticket Mr. Mendel because you were very very lucky. In all actuality I bet Mendel actually doctored his data and left out data that didn't match his expected phenotypes or his expected ratios. I say that I'm sure I hope that doesn't make anybody mad that I say that because it's like shocking to me that the seven traits that he studied all happened to be fully dominant and recessive to alleles and they each trait that he looked at was coded for by a gene on a separate chromosome that just seems kind of wild. We're gonna look at fruit fly wing shape and fruit fly color in order to talk about what we would expect to see if a gene is linked. How is that going to change the expected ratios that we would see with Mendel's giddy up? If anybody wants to come over to my house I currently have a very large fruit fly outbreak that I'm not exactly sure what to do with them. I definitely haven't like tried to identify if they are gray bodies. I think they all have normal wings because they're all flying around like mad. My son's cat Victor came over and Victor enjoyed the fruit fly infestation because he liked to chase and I guess eat the fruit flies so maybe Victor has to come back over and help me with my fruit fly infestation. In the meantime let's talk fruit fly phenotypes. You'll notice that we have two body phenotypes here. We have gray and we have black and I don't know if you can see this very well. I'm going to zoom in just so you can see. We have normal wings. Do you see those wings? These guys both have normal wings and normal is what they're called and then compare it to this. They call this a vestigial wing. Vestigial normal. Okay and look here's another vestigial wing. You kind of have to look close in order to see the wing phenotype but I'll just go ahead and put this normal normal vestigial vestigial and then this was black. Oops that's not black. Silly. What if I got that one wrong on the test? I would be very mad at myself. That's gray. This one's black. Do you agree that we just identified the phenotypes of the fruit flies? Easy phenotypes are descriptions of things we can see, things we can touch, proteins that we can just find. Awesome. The next question is what are the genotypes that lead to this and in order to figure out what genotypes are possible with each of these traits, we need to take a second to identify the pot like what are like let's name our gene and let's figure out who's recessive and who's dominant. So we have body color and we have gray and I'll just go ahead and tell you gray is dominant or black black is recessive and we have wing shape and I'll tell you right now normal is dominant and vestigial is recessive. Vestigial wings are not going to be super successful in the world so vestigial wings are something that scientists have propagated and so that they can study genetics. Oh thank you fruit flies. If now we're going to do two things at the same time we're going to try to imagine like we're going to look at all the genotypes we're going to think about the possible gametes all of this is normal even though in reality these genes are linked. Once we identify all the genotypes and the possible gametes that we have for these guys then we're going to look we're going to do some process we're going to make fruit fly babies oh I'm already starting projects in my kitchen we're going to make fruit fly babies and see what they look like we're going to look at our expected phenotypes like how and percentages and then I'm going to tell you what we actually see so keep in your brain stay focused with me here because this is a multi-step process first we need to see what would happen if these two what do we expect if these two genes are found on separate chromosomes and they do the Mendelian thing we've got complete dominance in both situations what are we going to expect to see well first of all um our possible genotypes do you agree that you know let's um I'm going to use the same letters gray uh what I don't like this I'm going to use blue and I'm going to go my possible genotype is I know I have one big G but I actually don't know if I have another big G or I could it could be heterozygous and it would still express the gray phenotype I'm going to do body types all the way down black is recessive and so I'm just going to do little g little g and I picked g randomly so you can pick any letter to represent this just be consistent all the way through I have um column three we've got another gray guy again we're not positive what that one is and then we have another black guy then we do our wing shape we have our normal wing shape dominant I think I did in for normal and again we don't know um and normal we don't know best digital is going to have to be homozygous recessive in both those cases you just identified the genotype of each one of these flies so far so good so far this makes sense now possible gametes our possible gametes in every situation where we see a little line we can't determine we we don't know because if those are heterozygous where that little line is if it's recessive it's going to give us different options than if it's dominant the only um possible gamete that we know for sure is this guy all of that guys gametes are going to have a little n and a little g because those are the only options do you agree that our gray normal winged home kid could be oops not that color this is the problem with lots of colors could be that that could be a gamete sure could be that that's a possible gamete for that guy if he's heterozygous could be this sure could be this do you agree that there are four possible gametes now let's take a look at this guy every gamete for this guy has little g but they could have little n little g but there's only two possible gametes for that guy similar situation for this one all of them have little n i'm just going to put both little ends there could have big g could have little g these are i did it all i did all my possible gametes for both situations are you cool with that this is what we would expect and then if we had heterozygous genotypes for all these guys then we would expect a quarter for this friendly fellow we'd expect a quarter of the gametes to be big n big g a quarter of the gametes to be big n little g quarter of the gametes to be little n big g and a quarter of the gametes to be little n little g right yes well let's do a cross i'm going to tell you we're going to cross we're going to define um okay i can do this i'm struggling to pick a color we're going to cross a heterozygous normal gray guy so it is big n little n big g little g times a homozygous recessive black vestigial guy little n little n little g little g how do you feel about this this is the cross that we're going to do and i'm going to do it on another page what so i'm going to show you what we're going to do the possible gametes for this home kid these are the possible gametes for that guy and these are the possible gametes for this guy i kind of want to grab these gametes in fact watch the magic i'm going to take this to the next page with us copy i copied that i'm taking it to the next page so that we can remember what we just figured out we figured out that these are my possible gametes that this is my genotype oh no this is this guy huh and this is my genotype oh my lord that was the worst idea i've ever had i'm going to stop this right now i'm not stopping it i'm just going to delete all this stuff cut goodbye i'm going to start over because we got this we can figure this out as we go ready i guarantee that wasn't the worst idea i've ever had we have our n gene and our g gene this guy phenotype black vestigial wings genotype is little n little n little g little g that's easy we've got that one i told you that this guy is heterozygous so we have big n little n big g little g guess what we're going to do we're going to make a square now our square i am going to do some magic here because our square is going to let us throw in our possible gametes we've already figured out our possible gametes but we're going to do it again all our gametes have to have a copy of the n gene and a copy of the g gene so let's do this this is the hard one so we could have that gamete we could have this gamete we could have this gamete or we could have this gamete those are all possible gametes produced by that fly our black fly is only going to make one gamete we're good yeah okay now what are our possible babies that you would expect to see we have big n little n big g little g what kind of fly is that that's going to be like the parent fly a normal gray fly normal wing gray fly this guy is also a normal winged but not a gray fly a normal wing black fly this guy gray guy vestigial winged gray guy vestigial winged black guy look and okay what percentages do you expect this is where it gets weird oh my gosh we did this whole thing and it's not how it is this is where it gets weird our expected percentages you expect 25 percent of everything so we're going to expect 25 percent of each one of these guys if the genes are found on separate chromosomes now before we go one step further i need you to look at those babies and i need you to tell me which babies are a word that we haven't talked about yet which babies are recombinant recombinant babies have phenotypes that are not like the parents phenotypes are not like the parents okay you're still with me i can tell you're still with me so who are the recombinant babies well to figure out who our recombinant babies are we have to go look at our phenotypes so baby number one is phenotype like gray normal parent baby number four is phenotype like black vestigial parent so who are my recombinant babies the normal winged black fly baby and the vestigial winged gray fly baby those are my recombinant they don't look like the parent great questions would be here are the parent flies here's a hitters i guess here's a homozygous recessive fly which possible offspring which genotypes are recombinant they're the ones that are expressing phenotypes that are not like the parent okay here's how you know that the situation is funkified if you have a linked gene okay so if these two traits are on the same chromosome they're not on separate chromosomes like all of Mendel's peas they're on the same chromosome and i don't know have we even looked at anything like that before if they're linked we have the n gene and the g gene on the same chromosome they can be really close together they can be not so close together if they're linked you're going to have big numbers oops big percentages of parental phenotypes and small percentages of recombinant phenotypes for example 40 percent of your babies instead of 25 40 percent of your babies show up with normal wings and gray bodies and 40 percent show up with vestigial wings and black bodies and what's that leave 10 percent show these recombinant phenotypes that's your clue that they're that the chromosomes were linked the genes were linked on the same chromosome you could have to evaluate data to determine is this a linked trait and how do you know um that's it okay you wouldn't have linked traits if you're just dealing with one gene you have to have two genes and they have to have complete dominance and then if you have that situation then you can do crosses to determine are these traits linked and if you end up with recombinant babies in smaller percentages then they are linked super curious to see how you held up with that one that's the hardest one the next two are well maybe the next one is not super straightforward um okay we'll get there you can do this keep going