 Okay, fruit flies have all sorts of really interesting characteristics and they're really easy to breed. You can make like little vials of fruit flies and you can buy different kinds of fruit flies and then do all sorts of genetic crosses which is really interesting and kind of fun to do and then you like make them drunk and count them and I don't think making them drunk kills them, but it might. Okay, but anyway, fruit flies are a group of critters that have given great insight into genetic patterns especially sex-linked patterns because eye color is sex-linked. So we have a dominant trait which I'm going to call R which is red eyes and this is the normal state of things. The other thing I want to show you here is that in fruit fly landia do you see that curved abdomen like that really round abdomen? This is a male fly and the kind of pointed abdomen is a female fly. I believe that pointed abdomen is about having a egg depositor like that it's like a tail for digging a hole and depositing an egg. So we've got phenotypes of flies here are a red-eyed male, a red-eyed female and then we have this recessive trait that I'm going to call little R and that's oops not red eyes it's white eyes and you can see that we have a white-eyed female and a white-eyed male. Well it just so happens that this eye-colored allele or eye-colored gene is found on the X chromosome. So our male does indeed have XY and this guy has red eyes so super interesting to think about this because he could have we know he has at least one dominant allele. Oh wait we know he's a dude and he only has one X chromosome so he has that's it that's his genotype I'm done he just has one big R to throw around the female is the one who look we know she has at least one big R because she's expressing the dominant trait however her other X chromosome sometimes you put it like this where you go I don't know what her chromosome is I don't know if it's a big R or a little R we know there's something there but we don't know what it is so you might make it a holding place. In a problem they could say you have a heterozygous red eyed female in which case you would be able to fill in the rest of this problem. Let's do the genotype of this white-eyed female what do you think that that her genotype is well we know she has two X chromosomes and in order to express the recessive trait she has to have two copies of the recessive allele and then our white-eyed dude the white-eyed dude over there he has to have one copy his X chromosome has to have that white-eyed recessive allele and he has in order to have the male characters he has to have a Y chromosome okay so this is another example we could do all sorts of fly crosses we could cross a white-eyed female with a red-eyed male I could cross I could give you a white a red-eyed female with a white-eyed male and then you tell me whether or not she is heterozygous or homozygous based on the offspring that we produce that's almost a test cross isn't it like if you did that if you did if you cross any female with this white-eyed male any one of our red-eyed females with a white-eyed male we that's could be a test cross and would help us determine the actual genotype of that female keeping track of your X and Y chromosomes when dealing with traits that are linked to the X and Y chromosome or X or Y chromosome it's super important to do okay inheritance patterns based on sex chromosomes we also have interesting inheritance patterns based on chromosomes not separating properly during gamete formation and ending up with odd numbers of chromosomes so that is called aneuploidian let's talk about that next