okay for this is [Applause] [Applause] yes for [Music] for for EX [Applause] [Music] for for [Applause] for for all right raise your hand if you're still working on the quiz was that a hand all right well everybody's done so we'll go ahead and get um started with the lecture so today we're going to be um Switching gears uh from meiosis mitosis we're going to talk about patterns of inheritance um how you know we look the way we are how are passed down from parent to offspring um and so this chapter chapter 12 these are the sections um today we'll go through the first two sections and we'll continue on Wednesday a quick chapter overview um when we talk about inheritance things we inherit uh we're talking about genetics and um has anybody heard of Gregor Mandel Mandel yeah yeah so mandelian genetics um involves two types of crosses monohybrid and dihybrid Crosses today we'll talk about what monohybrid crosses are and what they demonstrate um and then some methods that are used to analyze what some of those um ratios are and where those um genes are um segregated we do that using punet squares um and so we'll talk about that today and some extensions to Mandel some other traits um environmental factors and I did not put this sign cat here this is actually in your book so um it's been recognized that we resemble members of our immediate family more than unrelated individuals so that's something we all know um and that was recognized very early on but there was no coherent explanation for this so before the 20th century um there were actually two concepts that were thought to be the basis around heredity heredity occurs within species so humans um you know Dad it has red hair blue eyes kids have red hair blue eyes cat has red hair blue eyes the cat is also in the book this I did not include that but um and that traits are transmitted Direct directly from parent to offspring so that was one of the things that was recognized early on um but this led to a view that the traits resulted from a blending of the traits through a fluid like your blood this is actually where the term Bloodlines comes from um so it was thought the um this older idea has persisted in this term called Bloodlines this was thought that traits are passed on through the blood from parents but that's not how it actually works as we know now um and so this idea is that you're blending traits from Mom and Dad and and that kids will have this blend this intermediate feature um but this is really paradoxical because if blending occurs then why don't all individuals look alike um so you see here girl has curly hair boy has straight hair so if there's blending happening why aren't they looking more similar so um some early plant biologists started to do some experience with some hybrids so if you remember in week one of our lab when we did the tree tour we looked at all the trees in Adrien um we looked at some trees that were hybrids so they were not one strain one type of tree they were a mix between two different strains um to make a hybrid and so this guy Joseph Cole rder he in the 1700s he crossed tobacco strains uh to produce hybrid strains and so in The Offspring he noticed that they differed between both parents they they were different um the hybrid Offspring were not the same as either parent and he also observed some additional variation in the second generation um and so all that variation um contradicted the idea that traits are directly transmitted because those traits weren't seen in the in the first um set of Offspring in that first generation um then this guy ta Knight came along and he worked with PE Garden peas um P sativa is the strain name and what he did was he crossed two different strains that were each true breeding so true breeding means that if you self fertilize it so if you breed it with itself you're going to produce that one type that self so that means that it's a true breeding strain if you can self cross it it's going to be the same thing that's going to come out um and so he crossed the peas with green seeds to peas with yellow seeds so both of those were true breeding strains and we saw that the first generation only had yellow seeds no green and then the second generation actually did resemble both the parents so it had green in there and there were some That Grew with yellow seeds so this contradicted the idea of blending there wasn't an intermediate color between green and yellow that was formed it was one or the other so these are just some early um experiments that were done that kind of started to lead to this idea that you know things aren't really actually Blended they're not directly transmitted um through the blood um there's more to it so Gregor Mandel in 1822 in Austria he used the PE Plants they're a good me U model organism for these experiments um mostly because there was other research already out that showed that pea hybrids could be produced um there were a lot of varieties of peas available um there are some that have different colors of the flowers they produce there were some that have different seed colors like I just mentioned yellow or green some had round um seeds some had wrinkly seeds so there were just so many different varieties available that you could test they're small plants they're easy to grow um and they can be self fertilized or cross fertilized so does everybody understand what self fertilization Means versus cross fertilization self is you're doing it to itself cross is you have a different strain and you're you're Crossing them together fertilizing them together okay any questions here so how did mandelle conduct his experiments so um this is a PE plant with that has a flower that grows so this PE plant flower the petals can be either purple or white and all of these either purple or white they will have both male and female parts so the male parts are the anthers so over here these these yellow things they carry the pollen um and the females is the carpal which contains the ovules you don't have to remember these terms you just have to know that there's a male anther um a female carpel and what he did was he used the pollen from a white flour to fertilize a purple flower so would that be cross fertilization or would that be celf fertilization cross right cuz it's purple to White good so um he obtained pollen from the white flour transferred it to the purple flour and all the progyny had purple flowers so that was an interesting finding um and so just to make sure that there was no error in the experiment and that this is um you know if you re repr produced this he also tried to do it using pollen from a purple flower to fertilize a white flower so that gave the same results all of them had purple so this was called a reciprocal cross um and because all of these uh progeny were purple that led to the idea that the purple is the dominant trait and the white was the recessive trait so we'll talk about that more later but just kind of prefacing it now so his experiments usually were in three stages um and these stages are the different Generations that are produced so we'll talk about the F1 F2 and F3 Generations so um the first step was to produce true breeding strains for each trait that he was studying so in this example he would produce true breeding strains make sure that purple was crossed to purple um and then white was crossed to White then he cross fertilized these true breeding strands and so he then crossed purple to white or white to purple he did these reciprocal crosses to ensure the source of pollen is from both types and then he allowed the hybrid Offspring so those four purple offspring that we saw on the last slide he let those self fertilize for several generations and he counted the number of offspring that were either purple or white so they show each trait each form of the trait so um to show you this I'll show you an example of all of this um in a second but just to have it in words these were the three stages of how he did these experiments for any trait um and this example I'm using the flowers but um Mandel actually did this using seven different traits of the PE plant um and these are called monoh hybrid crosses because you're studying two variations of a single tra so if you look over here these are Mandel's seven traits first is flower color which we went over purple or white so the trait is the flower color the two variations are purple or white so that's the distinction there between the variant or variation and the uh trait um he also looked at seed color so yellow versus green and over here you'll see that the yellow is dominant just like the purple the recessive is the green he also looked at seed texture round versus wrinkled pod color green or yellow pod shape if it was inflated or constricted the position of the flower um the plant height so each one of these are traits and each one of these has two variations so that makes it a monohybrid cross some traits have three variations or more those are going to be called di hybrid crosses we'll talk about that on Wednesday but today we're going to focus on the monoh hybrid um cross does that make sense to everybody any questions there so the F1 generation is the first filial generation so that's the generation That's The Offspring produced by crossing the two true breeding strains so here we have the parent generation which is the true breeding purple parent and the true breeding white parent when you cross ize these you get the F1 generation and all of The Offspring remember were purple so that's the F1 generation this visible trait is dominant because it's masking the yellow the yellow is in in the jeans as we now know it but it's not showing up it's being masked by the purple in this first generation so therefore this is the dominant trade so the altern the alternative trait so the white would be the recessive trait does that make sense to everybody okay I assume you guys have probably gone over this before but I just want to make sure um I'm reiterating what I need to um they also uh he also noticed that there were no plants with intermediate characteristics so there was no blending inheritance so what color would we expect if these were Blended what it pink pink yeah so if you blend purple and white think of mixing pink um you would get pink but that's not what's being shown here we are only getting purple or only white so there's no blending um inheritance so his next step was to take each of the purple Offspring and have them self fertilize so when that when he did that this was the f two generation and when these are self-crossed um he notice that the white recessive color actually came back um and so although the white was masked in the first generation the F1 the recessive trait the white reappeared in some of the F2 individuals so he just did this by counting he Quantified so counted the the proportion of the traits and he created a ratio of a 3:1 ratio 3 three purple to one white in the F2 and then if you allow this all of these to self cross um so so far in the F2 plants we have 3/4 of the plants with a dominant phenotype so I say phenotype because we're talking about just the color and then a quarter of the plant had the recessive phenotype the white but then if you do some further self crosses he actually discovered that it's not necessarily A 3:1 ratio it's a 1:2:1 ratio and that's because when you cross this first dominant one you get all purple so that means that this one ended up being a true breeding strain this one was purple but when you self-cross it you get three purple one white so there's it's not it's a heterozygous dominant and we'll talk a little bit more about those and then the recessive is going to be have to be homozygous recessive so both of the AL will have to be white in order to produce all white flowers so this 1: 2: one ratio so one true breeding purple dominant two non true true breeding purple dominant and one true breeding white recessive so this is called a genotypic ratio because we're referring to genotype um we now know that there are genes and Al that that have these colors encoded on them and so um this F2 generation is disguised as a 1: 2: one ratio so the 3: 1 is actually 1: 2: 1 doeses that make sense so like the true uh true per parent that would never have any right to yeah if it's a true breeding purple parent it's not going to produce white unless you if you're self-crossing it to itself um if you cross it to something else that's not true breeding then you can't have white and that's all um analyzed through the pet squares which we'll go through in a second any other questions so his conclusions were that his plants didn't show intermediate traits no pink um each trait was intact or discreete so what passes from parent to off Offspring is a discrete entity so he called these factors we now know that these are genes and so for each pair one trait was dominant and the other was recessive and the pairs of the alternative traits that were examined happened to segregate among the progeny and he saw that alternative traits were expressed in the F2 Generation in that 3:1 phenotypic ratio so that was shown in the F2 Generation but in the F3 generation you can see the one to2 to one does that make sense so Mandel also had a Five Element model and so here's where I'll bring in some definitions the parents transmit these discret factors which we now know are genes each individual receives one copy of a gene from each parent not all copies of a gene are identical and the way that we describe those is by calling them alals and Al is an alternative form of a gene so the purple flowers would have if if it's a true breeding purple flower then it's going to have two alal that code for purple so if it's a purple flower but it's heterozygous so they have different alals it can have purple from Mom and white from Dad on the on the gene you have two different alals but because purple is dominant we see purple as the phenotype so homozygous trait is one that where you have two of the same Al and heterozygous means you have different Al any questions on that all right his fourth element was that Leal remain discreet there's no blending and fifth the presence of a Le doesn't guarantee expression so even if an recessive Al is in the um is on the gene it can be hidden by the dominant Al or it will be um and the dominant Al is what's expressed if you have a gene with two alals that are recessive then you will have the recessive phenotype showing so the genotype is an individual's complete set of Al and phenotype is an individual's physical appearance a lot of these genetic terms were adopted after Melle but we use them now since we have discovered all of this for the understanding of genetics so phenotypes expressed in a genotype so the phenotype is is expressed the genotype are the genes that are showing so if um we have one that you have a heterozygous trait so you have say let's talk about the flowers if we have um a gene like something a flower shows up as purple but you see that here let me actually go back to this so let's talk about this purple dominant um non-true breeding strain so this one shows up as purple because that's the phenotype but when you self cross it to each other you see that it actually does produce some white which means that this one was heterozygous so it had one Al that was purple one Al that was white so the genotype would have been we we I'll show you in the punet squares we do like big p Little P so that's yeah so that's the genotype the phenotype is the color that's being expressed so this led to this theory of the principle of segregation um and so this is in line with what we've already learned in meiosis so there's two alals for a gene that segregate during gamet formation you get one from each parent and they're rejoined at random during fertilization so the physical basis for alal segregation is the movement of chromosomes during meiosis so that's what's happening behind the scenes for us to see these F2 F3 generations and so on Mandel had no knowledge of chromosomes or meiosis it hadn't been described yet um he deduced this principle based on trait ratios but now we know where it comes from so H how many people have like done a punet square before okay majority of people great so um just a quick reminder the female genotype is listed on the side and the male is listed across the top so here uh we're seeing that the female has a big p capital P Little P and the male is the same so is this homozygous or is the are these heterozygous what are what are they heterozygous because you have a big p Little P for each one what color would these be if we're referring to flowers louder purple purple yeah because the big p is the purple Al the little p is the white Al so because the white is recessive and we have a big p the big p is going to mask it so the genotype is big p Little P but the phenotype is purple and so the way you do this is you go across and down and you then can see what that would be so you add them together and so this offspring would be a little p Little P so what color would this one be white okay so you do the same thing here this one will have a big p Little P this one will have a big p little p as well and this first one will have two big P's so what color would this one be purple and is it true breeding or non-true breeding sorry I hear both big p big p it's going to be true breeding because it has two of the same Al this one is also true breeding white this one's true breeding purple so these three will have purple flowers this one will have white flowers but if you look at the genotype this one is true breeding these two are not but they're all purple and this one is true breeding but it's white so that's the 1 to 2: one ratio for the genotype but if you're thinking phenotype you have a three purple to one white ratio does that make sense so um each true read parent makes only one type of gam so this is now putting it all together all of the F1 generation are purple here in this example so here we have um is this a little p yeah so um a heterozygous dominant purple with a white parent and so you can see that all of these are purple in the F1 generation um and then once you do the cross with the um the big p Little P then you see this 1: 2: one ratio so again the Vicky viy are homozygous dominant homozygous because they're both the same dominant because it's purple and capital heterozygous is because you have both but it's still purple and Little P Little P are homozygous recessive do all those terms make sense any other questions okay well that's it for today will continue on Wednesday