hey students it's me dr davenport and this is xeno the cat uh we are here for your exam for review um so you know you're as usual you've done three chapters i'm not going to talk about um chapter 11 or 35 here because honestly they're pretty straightforward um and there's not a lot to practice with per se but with chapter 10 because you're doing all those punnett squares i think some of that can get a little tricky and definitely need some practice so that's really where i want to focus today so let me share my screen with you let's do some practice questions together so first let's just kind of review a concept here do you remember what a carrier is so take just a second and think about um what the answer would be to this question you can always pause when i ask you questions and then come back when you're ready so i hope that you picked b now carrier remember means i have a recessive thing that i could pass on to my offspring but i am not affected so here where you're seeing these genotypes listed what you see is this person has two dominant alleles so all they have is what they're affected with and that's all they can pass on they're not a carrier this person has two of the recessive alleles they can pass on that but they're also affected the only option where they don't have whatever this code's for in their phenotype but they can pass it on to their offspring that is this one so this is also a good chance to just review really quickly what do we call these remember we would call this genotype homozygous dominant this genotype would be homozygous recessive and this genotype would just be called heterozygous one of each now i could also call this a carrier this person who has a heterozygous genotype is also a carrier so with that as you know a reminder try out this question jane is a carrier for the recessive allele that causes cystic fibrosis and john is homozygous dominant how likely is it they will have a child with cystic fibrosis so pause this and give that a try and if you're back let's talk about how we would set this up if jane is a carrier she's going to have a capital a lowercase a dominant and recessive now you cannot pick any letter you want um i often like to as you write out the genotypes i often pick the letter a because the capital and lowercase look so different some of you may have tried a c but i feel like a capital c and a lowercase c they look awfully similar so let's do this let's say so jane is one of each and again it doesn't matter what letters you used she's a carrier but john is homozygous dominant so i'm gonna share my screen i'll stop sharing my screen so that you can see me nice and big for a second if he is homozygous dominant then i would set him up this way so when i fill this out what i see i see a couple of options where the offspring look like john homozygous dominant no cystic fibrosis is possible i see a couple options where the offspring are heterozygous but they would be a carrier like monk right they wouldn't actually have cystic fibrosis so what i'm actually seeing here is a zero percent chance it's impossible because in order to have a recessive allele in your phenotype you would have to be homozygous recessive and they are not so for this answer i hope that you put zero percent that it is not possible so a right okay so let's do a couple other things um for review and then i'll give you a couple other questions at this point we've now talked about dominant and recessive also i apologize if you can hear my cat eating in the background i live in a very small house there's only so many places to do things so um let's talk about dominant versus recessive now i can't remember if i put this slide in your notes let me talk you through it whether i did or i didn't i think this is a really helpful visual if you know what you're looking at so here's what i want you to imagine you meet some alien race and they have striped skin and some of them have vertical stripes on their skin and some of them have horizontal stripes on their skin now i want you to imagine that this alien's stripes it's a gene that causes it and it's regular dominant versus recessive so now i want you to see what here every time i put this plus this i'm saying what's each of the alleles that this alien has this alien is heterozygous this alien has one allele that codes for vertical and another that codes for horizontal now if vertical was dominant then what this alien would look like is right here so it would be carrying the horizontal stripes it could pass it on to its offstring spring but it would have vertical stripes so this is what you've learned about okay so dominant plus a recessive in my genotype shows the dominant in my phenotype but wait because genetics isn't always so simple it's actually why we have such interesting traits and so many of them so many possibilities sometimes genes aren't simply dominant and recessive you learned about two other examples incomplete dominance and codominance so let's talk about what if we're talking incomplete dominance same alien race but now let's say actually each of these genes vertical horizontal they're incompletely dominant remember that means you get an in-between this alien has this genotype heterozygous one of each but its skin is going to have an in between diagonal stripes this is like that red plus white gives you pink flowers or straight plus curly hair gives you wavy hair you get an in between if they're in completely dominant so then what about codominance well with codominance in this case both are going to show up in full force so now let's say you have the allele that codes for vertical stripes and you have the allele that codes for horizontal stripes if they are codominant boom you get both right so really what i want you to see is that sometimes we can't just know what alleles do you have because in this case it's the same genotype every single time sometimes we need that extra piece of information and what is their behavior like because once we know what their behavior is like then we can tell you what the phenotype would be so with this in mind let's do some practice let's start with incomplete dominance you've seen this question this is actually the one in your homework so i want to ask you a different one slightly different the one in your homework starts out reminding you that the alleles for curly and straight hair exhibit incomplete dominance and i asked you if a child has straight hair let's do a new one not in your homework it's going to look the same but now i've changed it to if a child has wavy hair maybe before we do that let me show you how i would solve it because i bet y'all got there but maybe i can show you an easier way so let's actually go back to this straight the child has straight hair when i saw these like a child and what's true of their parents i am often thinking of a backwards punnett square so i'm going to stop my screen shower and make me nice and big and the board nice and big let's talk through this let's remember these sentences the alleles are curly and straight in completely dominant the child has straight hair so here's what that tells me if straight and curly or incompletely dominant then here's what i know if a person has curly curly that's the alleles they got one from each parent when they're gonna have curly hair if that person has straight straight then they're going to have straight hair if that person is heterozygous because these are incompletely dominant they're going to get an in between they're going to have wavy hair now wait andrew davenport why are you giving them separate letters why isn't there a lower case and a capital because remember with incomplete dominance or codominance since neither of you shadows out the other since neither of you gets to override the other you need to get your own letter so this was the first sentence this is what it told us right that second sentence said what if the child had straight hair what could be true of their parents so i saw this in what i kind of call a backwards punnett square where i say okay i don't know much but i know that the child must have ss because she has straight hair there she is so here's what i can now guess or no really she had to have got that s from one parent and that us from the other parent no i don't know the other allele that each parent has but i can make some guesses maybe this parent has another s so if that's true then this parent could have straight hair maybe the parent has a c and if that's the case sc then they would have wavy hair but you know what they could not possibly have is curly hair because you'd need two c's and they clearly have at least one s they cannot have two c's same thing with the other parent maybe they have straight hair ss maybe they have curly hair sc but they sure as heck don't have so i rated them wavy hair sc but they sure as heck don't have curly hair right okay so now that we know that one and you have kind of an easy way to solve it i'm gonna leave this punnett square nice and open and ask you to go back and look at this next question what if the child has wavy hair and now i want you to tell me what's not possible about her parents take a second to do this i hope you started again with wavy it's going to be 1s and 1c and it does not matter which order you put them in s c c s doesn't matter again doesn't matter which parent you put on top which parent you put on the side it doesn't matter you're still going to get to the same thing so i'm going to tell you the right answer and then let's talk about how we got to it the one that is not possible whatsoever is d it is not possible that both have curly hair because if both have curly hair then i would have to have cc cc but i don't so you see on top sure that's fine but i have an s over here both parents could not possibly have curly hair to make this one another possible answer here i mean it's not i'll only ever put one right answer but also it's not possible for both of her parents to have straight hair because that would mean ss and ss then where did she get the c from right a b and c are all totally possible you can make it one has straight one has curly sure that one can have uh sorry one has straight one has curly shirt this one could be the curly and this one could be the straight or one has straight and one has wavy sure that could be this right so you can work that so that all of those make sense except d just can't happen all right let me ask you your next question so that was on incomplete dominance let's talk codominance you saw this question in your homework jane has blood type a john a b jane has five children but john is only the father of four ooh scandalous who'd you sleep with jane so now you had to pick which child is definitely not john's before i ask you a new one because again this one's from your homework let's just remind ourselves how did we solve this well again pundit squares so uh and and again i'll make my board nice and big let's remember jane has blood type a john has a b so i'm gonna do my punnett square i'm gonna put john first he's an easy one if he has blood type a b he clearly has an a and a b that's it that's what he's got jane has blood type a so i know she has at least one a i don't know what her other allele is though maybe it's an a maybe it's an o because a and o o is recessive so she'd still have blood type a but it can't be a b because if she had a b here then she'd have blood type a b so all i know is either it's a a or a o now you could if you were feeling like spicy you want to do extra you can fill this out you can say okay an a and an a and a b here it's a guess okay that could be an a and an a or it could be an a and an o this could be an a and a b or it could be a b so you could fill that out and if you do that and now we go back to that question and we see okay so which which child just does not show up on our punnett square you would see jeb is just not possible john has no o to give but jane might so jeb is definitely not their child i would recommend don't even bother filling in your punnett square it's a lot of work and in this case you just don't have to here's what i would recommend doing instead when you see a question like this on the exam or just in your future once you just set it up all you have to do is go through and just say can i find ao somewhere sure a o move on can i find a a sure a a move on can i find if i skip to jordan a b sure a b move on but this o o i just cannot make that work anymore okay so with that in mind here's your next question it's a little trickier but i bet you can do it jane has blood type a still but now john has blood type b now i want you to tell me with your understanding now of john which one is not possible all right let's set it up together we're gonna leave jane the same either she has a a or a o and we don't know which so john has blood type b so i know for sure he's got a b but his other allele well maybe it's another b maybe he's b b maybe it's an o because if he has a b and an o it was recessive so that would still get some blood type b but this is definitely not an a so i'm not going to bother filling in this chart because it gets pretty complicated at this point here's all i have to do can i find josh with ao on here sure a oh that works can i find jess with a a no john has no a to give well what if i keep going what about jeb oh oh sure yeah if he had an o and she had no i can find them or jordan with genotype a b can i find that sheriff or square or gen with bo can i find that sure but nowhere on here can i find jess with genotype a a so b would have been the correct answer here so you can give yourself lots of practice by just changing up the parents uh blood types and figure out so what does that mean about their offspring right okay so let's wrap this up with just a little bit of talk on sex-linked genes you saw these questions in your homework and so i just want to make sure to be super extra clear a male with a harmful x-linked gene will pass the gene to or a female that is heterozygous will pass the gene to how do we figure this out let's do the male first because that's the easy one when we're talking about sex chromosomes we are no longer talking about everybody's got two we everything we just did everybody had two genes for blood type two genes for cystic fibrosis right you name it we had two but it's not true anymore when we're talking about males and sex-linked genes because they have x y this has different genes on it than this so let's talk about who he would get these from and who he might pass them on to so this male has x y and i said he's got this harmful gene on the x chromosome so i'm just going to put a little little squiggle there to just show hey there's a gene here and it's harmful and we're wondering who he's going to pass it on to before we even say that let's say who did he get it from one of his parents gave him this ex and one of his parents gave him this y his mom his female parent clearly gave him the x the female only has x's to give the male parents would have given him the y so we already know which parent each of these came from now let's talk about when this male makes sperm half of his sperm will carry the x and half of a sperm will carry the y if the y carrying sperm meets an egg number eggs always carry an x so this osprey would be x y so this offspring would be male that means he got his y from a male parent and will only pass it to male offspring if he passes on the x and it meets the x in the egg now it's xx it's gonna make a female so in this case the x's only come from females and go to females so in this one this is the one where you would say you know 100 of his female offspring are gonna get this and zero percent so all and none all female no males but wait because this is totally different for females so let's talk about it and again this is kind of why sex chromosomes are so neat because it really is different between males and females so the male had xy and it was all females no males that he would pass the x to the other question in your homework was well what if i now have this female and she's heterozygous so here i'm just going to put the little swiggle on one of them because heterozygous one of each so she has a healthy and not healthy okay so who did she get these from clearly she got this from one parent and this from the other i don't know which she got it from this could have come from the male or this could have come from the male from female from female we don't know because each of her parents gave her an x so i don't know who they came from when she makes eggs half of her eggs are going to pass on that half of her eggs are going to pass on the unhealthy one and it's not the female that decides or determines the sex of the offspring it's the sperm so if an x carrying sperm meets this or a y carrying sperm meets this she could pass this on to males or females either way if she passes on this one and it meets an x-carrying sperm or if she passes it on and it meets a y carrying sperm this could make females or males right so this is how we come to this answer of kind of half or at least there's a 50 chance that her females would get it and the 50 chance that her males would get so now we're talking half and half or 50 50. so you see it how the sexes really do differ only especially when it comes to these chromosomes though okay i hope this helped i hope you got good practice uh and i hope you all ace exam four