okay don't worry i have not forgotten about the ap bio crash courses we are doing them okay totally didn't forget hello everybody i'm kara and today we are going to be doing unit 5 heredity which is going to be very epic as you can see we're talking about meiosis and mendel and all that good stuff so why don't we just get into it so in the last unit uniform we talked about mitosis right and mitosis makes identical daughter cells right if you want to grow right you want to just duplicate the exact same cell you use my toast but you know that like you're not the exact same person and your parents would be very very creepy if you look exactly like both your mom and your dad at the exact same time that that would be really weird so somehow we had to combine both your mom and your dad right so we know that your mom has like cells body cells with 46 chromosomes you know your dad has a body filled with 46 chromosomes and you know that to make a kid to make a zygote right you basically need an excel from your mom and you need a sperm cell from your dad they need to join up like cool kids and they have to make a zygote you but you have 46 chromosomes so if you have 46 in the sperm and 46 in the egg and they come together and you make 46. wait no that's not how addition works 46 plus 46 is not equal to 46. so clearly something is wrong here somehow we need to make it so that the egg and the sperm have 23 chromosomes otherwise you're going to only have 92 chromosomes which is not right also just another thing to remember make sure that you remember that this is called fertilization right basically you get some stuff from your mom in the egg you get some stuff from your dad in the spurs and you make yourself a psycho okay so basically the way you make these egg and sperm cells right they're not normal body cells we need a new type of cell division that actually has your chromosome right you go from 46 to 23 somehow and that is called meiosis all right so why don't we talk about how meiosis works and i really think the best way to remember how any any process works right is to just think of the endpoints right what do you start with what do you end with and then it's easy to like figure out the steps in between if you know the starting and ending points so for example right mitosis you have like 446 chromosomes let's just say we have a six chromosome because i have two ladies to draw 46 chromosomes then basically this guy divides up into two cells with the exact same chromosomes except now they're not no longer duplicated all right so this is mitosis you make two identical dollar cells now meiosis is a bit more complicated because now you have to keep track of which one you got from your mom and which ones you got from your deck so let's say you have like three chromosomes from your dad right half of them from your dad and the other half are from your mom and basically you know that your mom and dad have like the same types of chromosomes right either your mom and your dad both give you a chromosome one each of them give you a chromosome two each one give you a chromosome three all the way up so they both give you a chromosome 23 which are just your sex chromosomes but basically we'll number these right their mom gave you a complete set right one two three and your dad also gave you a complete set right one two three and basically what meiosis does is it randomly puts like all these chromosomes into different cells and you can see right like mitosis basically keeps the number of chromosomes the same with one division right so we want to divide again in order to have the chromosome so if you multiply by two every time you divide you go two and you can do another two each of these guys split into two and you're left with four daughter cells each with half as many chromosomes and each of these things are randomly distributed let's just chuck them in there and each of these dollar cells is basically a gamey or like an egg or sperm cell now also keep in mind that each of these has to have a complete set of chromosomes right you can't just give your kid like only a one and a two does that be sad right your kid's losing out on the three come on you gotta give them all the type right so basically like each of these have a full set so let's say it's like one one three i don't know so you can see right we started with two ones right we started with two twos two blue threes and you can see they're all in the cell somewhere all right so now we know the start and end points of meiosis right you start with a cell a full 46 chromosome cell with duplicated chromatids right and you end up with four separate cells each with half as many chromosomes and each chromosome is not duplicated anymore and your mom and dad's characteristics are randomly chucked in there and so it's important to note about the randomness this is one part of sexual reproduction right the fact that we have two people coming together is the fact that we randomly put these chromosomes in our gaming right so that's one way we get genetic diversity okay so why don't we actually talk about how we get from a to b how do we get from the start point to the end point so basically the way i like to remember it right if you have four daughter cells you need two divisions right each division divides it into two so if you need to get to four you have to divide it twice right and essentially each one of these divisions is just a mitosis right so meiosis is basically two mitosis all right so let's do mitosis once right so you know that the first stage of mitosis is prophase so in meiosis this is called prophase one and basically in mitosis this stage is just setting up for division right your chromosomes condense stuff gets connected to the centrioles all that good stuff your nucleus membrane dissolves all that stuff but in meiosis you want to generate a bit of variation so in prophase they also prepare except they do a little bit more fancy stuff called crossing over crossing over and basically this is all you have to know about prophase one the one important thing if you have to know anything about meiosis prophase one is crossing over happens so basically these two guys pair up these two guys pair up these two guys pair up they have the same number right if they're both chromosome three that they're both chromosomes they pair up and basically crossing over is literally what it means right you see these guys are crossing over right they basically switch parts right they basically exchange little parts of their chromosomes so now there's a bit of variation right and not entirely your dad's chromosome it's not entirely your mom's chromosome so that is another way that meiosis generates genetic diversity right it randomly switches parts between your mom and dad's chromosomes and basically all the stuff that happened in mitosis prophase also happens in meiosis profiles also just a little bit of terminology right basically the parts where they crop like where they switch over is called chiasmata right the x's that they make right like this x right there it's called the modem and basically the thing that holds them together is called the synaptonemal complex none of this is that important i doubt you'll actually have to know the stuff but i'm just saying it in case it comes up just to refresh your memory if you got note already okay so why don't we move on to metaphase now so we're still on the first mitotic division so it's metaphase one right and basically in prophase all the stuff got connected to the centrioles right all that good stuff and basically metaphase is the exact same thing as mitosis metaphase right basically the things that are already paired up right these guys are paired up all of them are paired up they basically align at the center so you got this pair at the center you've got this pair at the center you got this pair all aligned at the center metaphase i just remember at middle right m for middle a line at the center okay now the next phase what do you think it is look at mitosis and it is anaphase pmat very cool so we're still on anaphase one now and once again this is exactly the same as mitosis except this time instead of mitosis where it splits off like individual like of these chromatids it just splits off like the entire chromosome so basically the your mom's chromosome one will split off from your dashboard with someone and now they'll go separate ways so what it looks like after anaphase right you basically snatch your like one of these right let's just say uh your moms went this way your mom's two went this way your dads one and three went this way as well and then same on the other side okay so now you can basically see right we have the number of chromosomes now instead of having one copy from your dad one from your mom you only have half as many chromosomes each of those chromosomes are still duplicated right but now you have half as many you only have one set of one two three in a normal cell you have two sets of one two three and this one you only have one set of one two three and as you can see these chromosomes separate randomly so there's one place where genetic diversity is generated and then telophase is basically just where it extends it like started blobbing like a cool kid and eventually cytokinesis splits it like in normal mitosis okay so now let's move on to the second mitosis okay so after telophase and cytokinesis you're left with two cells right and now they both have half of many chromosomes right you might have started with 46 your deploy number but now we're at half of many right halfway right diploid is two half weight is half very cool so now we do the second mitosis right now it's on the second version so we call it prophase two and basically what's cool about the second mitosis that happens right the second division isn't exactly like mitosis okay like literally it's exactly the same so prophase is just break down the nuclear envelope condense your chromosome detach stuff very cool then metaphase you align at the center right very cool and then after this and after we're done with metaphase you go to anaphase and just like in mitosis the actual chromatid right the identical chromatids on this one chromosome that may have been changed by crossing over now split apart so at the end of anaphase you guys have been drawn to other sides so this is how it looks after anaphase and then we finally go into telophase so now it starts blobbing and then eventually you guys split apart by cytokinesis and you are finally left with what we said we would end up with four epic daughter cells epic we are finally done with meiosis now keep in mind that like these are not like purely your dad they're purely your moms right remembering crossing over some parts of them might have like flipped over so that might have changed a little bit but this is what you basically end up with so you started with a haplet so you started with a diploid 46 and you ended up with a haploid 23. now if you don't want to memorize the entire like sequence although i would recommend you do because it makes it a lot easier to understand basically just remember you start with a completely normal body cell and you end up with four daughter cells each with half of many chromosomes and non-duplicated chromatids and basically the way i just like to remember meiosis without having to think about it at all to think of it as two mitosis right like the first time you split up homologous chromosomes right like your ones from your dad and your mom are cosmologists because they both have the same number and then the second time you split up the chromatid right basically they're exactly the same you just split them up like completely normal mitosis all right so now that we know how meiosis works and how it generates genetic diversity now we can start talking about like how that genetic diversity we could actually use math to solve that and basically the dude who made the song possible is mendel okay now we're going to talk about mendelian heredity so we basically already know that you basically get one step to your mom one step from your dad okay and basically what mental side is that each trait in your body is controlled by these one set from your dad one set for your mom and it basically called different versions of the genes alleles okay so alleles are literally just versions of a gene you don't have to think about it in any other way just know that they're versions of a gene and basically these genes which are part of your genotype right your genetic code right it basically starts with gene literally genetic code influences your phenotype right like based on what proteins your body makes based on what genetic code you have your appearance is affected right like how you behave like what color care i have it's all phenotype right what what it looks like on the outside all right so this is the basic terminology now let's just talk about the most like common form of inheritance that mendel studied right basically that's dominant and recessive alleles so you got your dominant alleles right basically um let's say you have a gene r mendel would represent it with a capital r and this is basically the determining allele right if you have this allele it will show up right and then recessive is the little lowercase thing and it only shows up if there's no dominant only shows without dominance all right so why don't we just take for example there's not a real example but let's just say the dominant allele r gives you black hair right and the little r the recessive allele will give you brown hair right now basically if you have rr right let's look at our definitions it's a determining factor right so if you only have the dominant you're for sure you're going to get the dominant right like literally the dominant one is determining if it's there it's for sure going to determine what you look like so this means you have black hair and because you have two dominant alleles it's called homozygous right homo means the same so that's how you remember that homozygous means two of the same thing and then dominant means you have two of the same dominant allele okay now it's a bit more trippy when you have r and little r right but because then you have a black version and a brown version so which one's gonna show now obviously the dominant one is gonna show by our definition so this guy has black hair and this is called heterozygous right because hetero means different and then finally let's just say we did like rr right now in this case it only shows without the dominant right but the dominant is not there so essentially this guy is going to have brown hair and what do you think it's called right if it's homozygous dominant what is this one going to be called that's right it's homozygous recessive all right so now we know basically how leo were basically one art is from your mom one hour from your dad and when they combined we could basically predict what's going to show up based on whether it's dominant or recessive okay but because biology is not biology without a little bit of math i don't know whether that's a thing but mendel decided to add in a little bit of math there so you gotta know the math this is like it's pretty simple math but you gotta know it okay and basically the question we're trying to answer right is let's say we have like your mom have two dominant alleles and your dad have like a dominant and a recessive allele what are you going to show up right what probability either they have black hair what's the probability of brown hair right now you can basically logic it out right like basically your mom's randomly going to give you one of her two alleles but they're basically the same thing right so she's for sure gonna give you an r right and your dad has a one-half chance of giving you a bigger and a one-half chance of giving a smaller right so essentially just by looking at it you could basically say that there's one half chance of getting a big r big r and a one-half chance of getting a little r little more and that means that no matter what you're going to have black hair right but just looking at it it's boring okay we want to make beautiful diagrams we want to we want some not something nice to look at okay so now we're going to make something called a punnett square okay and basically these guys are kind of epic if you get like more genes or something or if you're like one of us do it quickly you basically just put each allele one place right you have r r you have r little r and now you just write whichever one it corresponds to right so r r r r rr okay so right here you can see that two of the four squares are filled with this guy so the one half chance of this two of the four are both of this so there's a one half chance of that and maybe that means that no matter what you're going to have black here so now the more interesting one is if you have two heterozygous pyramids come together now this thing would change to a little r and this would become two little arms right because it comes from here comes there okay so now only one of the four squares is homozygous recessive only one of the four squares is homozygous dominant and two of the four squares are heterozygous so that means there's a one-half tens of heterozygous and one-fourth chance of both the homozygous right but all three of these results in black hair so you have a 4 chance of black and a 1 4 chance of brown alright so that's basically how you do it for one gene right basically this one gene has two versions you have one for your mom one for your dad and basically this is how you would calculate what the probability of getting a certain pair from both your mom and your dad is now what happens if we want to talk about multiple genes right like let's say there's another one like q right that represents like blue eyes i don't know why blue eyes would be dominant but we're just going to go with it and q is black eyes let's say even though probably that's going to be dark brown goddamnit and then basically we want to see given that your mom and your dad both are heterozygous for both blue eyes and for black hair what is the probability you also get blue eyes and black hair so why don't we do this logically right so your mom is going to be rrq and your dad is going to be rrq so basically the way they teach you in school right you just draw like a really big punnett square right and basically you just do it this way okay so basically what they tell you to do is they're like what what possible pairs could you get from your mom and your dad right you get an r from your mom and r from your dad you could get a little heart from your mom a bigger from your dad you could get a big arm from your dad a mom a little hour from your dad and you can get both little rs from both of them right so let's just write those in and then the same thing for your cube right you could get a cue from both your mom and dad you get a cue from your mom little cute from your dad you get a little cute for your mom and big q from your dad and you could get two little cubes and then you just fill in this whole thing it's kind of nasty now my approach is a bit simpler right basically it's asking how many ways are there to get black hair and blue eyes so let's see what the probability ignoring the blue eyes of getting black hair we already know that's three-fourths right okay and then if we just look at only blue eyes there's a three-fourth probability of just getting blue eyes if we ignore the black hair so now the probability of both happening this is not like easy probability right if it's and you multiply them if it's or you add them you basically multiply these right because you want black hair and you want blue eyes so your answer is 9 16 without actually having to do a really big punnett square you can just do too many kind of squares and then solve for the actual answer another thing you might have to deal with is like pedigrees right basically they represent family relationships right you might have a circle to represent a woman a square director than a man and then if you want to represent they had a baby together you just put a cross there and then you do that and very cool now they have a bunch of kids epic so if they had a girl a girl if they had a girl another girl and then if they had a boy you do that okay so let's say we were talking about taste accidents right and that's basically going to be a recessive disease right if you have two of the recessive allele you're going to have to then basically if we wanted to say that the woman had tay sacks then we would put her in a darker color right shade her in and then a question we could ask is like we know that our mom is a little little art unless they were given that the dad is big r big r then what are the probability that our kids have little our little r right and basically that says one half right because there's guaranteed to get a little r from mom and they can only get it if they get a little off from dad so it's one half so essentially what about one half of the children should have tazak so that seems legit okay so this is called the pedigree just know like the symbols right basically if you have a circle it's a woman if it's a square it's a dad and if you have a line connecting them they're related okay so now i basically touched on this indirectly right but the two laws that you have to take away from all the stuff we've been talking about are law of segregation and law of independent assortment so basically any gene that follows mendel's rules right basically you have a like two versions right and they both come together for your mom and your dad they follow these two laws so segregation basically means that if your mom has an r and r they're going to segregate inner games right each gaming is only going to have one of these alleles right segregation split them apart now law of independent assortment is if you have like rqq how rr is split up among the gameys is irrelevant of this guy right like this guy's gonna split up completely separately rr is gonna uh split up completely separately law of independent assortment just means that two different letters right two different genes are not affected by each other at all now of course the problem is that these laws have their exceptions so now the last thing we're going to talk about today is the exceptions to all these rules so the first exception i want to talk about is incomplete dominance right and that basically means that like if you have an r and an r this is actually going to be different from big r bigger right so let's say r like a protein right i don't know like metabolizes lipids for like hazard or something right then essentially what incomplete dominance means is that if you have the big r and the little r it'll actually produce less of the protein than big r big r right because only the big r actually produces the protein and if we have little our little r it's actually going to not produce any protein whatsoever so no protein a little protein and a lot of protein so that's why we incomplete dominance basically when heterozygous is actually not as much as the like homozygous dominance it's incomplete right like the the big r by itself is not enough to completely overrule the recessive allele now the next one is codominance which is really really similar i honestly keep getting confused between the two but basically my understanding is that codominance means that both alleles code for slightly different things so essentially i think a really good example is blood groups right basically your blood have like things on the surface right and there are two types of them right and basically an example is like if you have r a and you have rb right then you're going to have both a and b like molecules on the surface now if you have r a r a you're only going to have a right and if you have rb rb then you're going to have only b so both of these are dominant right they both result in a phenotype right but like and both of them could be together but neither is like completely dominant over the other one now your blood group which is a much more familiar blood group is actually controlled by multiple alleles so that is another exception to the rule so instead of just having a dominant and a recessive or just two versions of the allele you might have multiple versions and in the blood group there's actually three alleles there's not i a there's an ib and an i little i so if you're a b you have an a and a b if you have i a little i or i a i a then this is going to be an a type blood group now if you have i b little i or ibib then you're gonna have a type b and finally if you have two little lines you're basically gonna have zero right you don't have any of the other things you're gonna have an o because you don't have an a or b there's something called plyotropy which basically means that one gene affects multiple traits right so that's what apply trophy is and then polygenic inheritance basically is opposite right multiple genes affect the same thing and basically the way i remember the difference between the two is like plyotrophy right like i don't know it kind of sounds like it's affecting multiple things but polygenic means multiple genes right so essentially hydrogen has nothing to do with multiple genes is one so it must be one gene doing multiple things but polygenic has a gene literally in it so it's multiple genes affecting the same thing okay so now one of the biggest exceptions that you're going to have to know are linked genes right basically if multiple genes are on the same chromosome right the only way they like let's say there's a gene a right here and then the gene b right there the only way that these two things could split apart as if you during crossing over that very exact spot switches over with the other chromosome so basically the farther apart a and b are the more likely they are to be completely independent of each other but they're still linked as long as they're on the same chromosome and when they either on sex chromosomes right which are your x and y chromosomes this is called a sex-linked gene now what's interesting about sex-wing genes is that they're completely different right because a boy and a girl like get different x and y chromosomes right so essentially the way we represent genes on an x chromosome we do x a and x little a and let's do the example of hemophilia which is an x-linked recessive disorder so if you have two x-a's right then you're gonna have hemophilia right so remember girls have xx right and boys have x1 so essentially whenever you like have a girl and a boy together you basically have two x's and one x one y so essentially that means that the girl needs two a's in order to be sick but if the boy only has one aide right he's already sick right because the no dominant allele to mask the recessive allele so that's why boys are a lot more affected by excellent diseases right so in hemophilia we're let's just do an example so let's say that your mom is a carrier right she has one version of the hemophilia gene right and let's say your dad is a hemophiliac right then that basically means he must have the recessive allele so now if we do a punnett square real quick we basically get an xaxa x a x a x a y and x a y okay so basically they have a daughter right these two are daughters right there's a one half chance that they have the hemophiliac there's one half chance that they're carrier right they have the diseased gene but they're not actually diseased right if they have a sun then there's still a one-half chance right because only this guy is going to have it this guy is not okay what happens if we make this x a okay then this would become x a little a so if the mom doesn't have a recessive allele it's impossible for either the like daughter or the son to get the divine right because no matter what your dad's gonna give the son the y so there's no way the sons could get it and your mom's always gonna give them your daughter at least one of the dominant alleles so they're protected okay very nice all right so now the last important thing you've got to know about linked genes is recombination frequency okay and basically this is what happens if you cross like r r q q with little r little r little q little cube and you basically find out how many of them do not look like either of the parents right because basically we want to see how many times like this big q splits up from this big r right now basically for this cross there are four types of offspring right there's rq there is rrq there is little r little rq and little r little r little lock q little q okay so it's actually what recombinant frequency measures is how many of the offsprings are different from both of the parents right so this parent is black hair and blue eyes this parent is brown hair and black eyes right so essentially these two are the only offspring that are going to be different from both parents right so essentially if we're given that the percentages are 40 17 18 and like i don't know what what's this last thing okay 25 then essentially our recombination frequency is just the sum of these two percentages right so our answer is just 35 okay cool but that is it alright thank you guys so much for watching i hope it was helpful as always if you enjoyed the video leave a like and subscribe for more thanks for watching again and see you guys next time