hello bisque 130 this is the beginning of recorded lecture 34 uh still in this genetics chapter so everything we talked about last time in the last recorded lecture was mandelian genetics about this you know Gregor Mendel and we talked about mendelian inheritance patterns all this stuff dominant recessive all those fun things now it's talk about something different non mandelian inheritance so it it is true that there are many genes and traits that follow everything we talked about last time but there are exceptions to this so I double underlining this because there are going to be several things underneath this but yeah for the next while we'll be talking about things that sort of break slightly break some of the rules that we defined last time one of these is something called polyenic inheritance so what we learned last time was that one gene controls one trait there was one gene that controlled the phenotype of whether the pea plants were purple uh or white but in polygenic inheritance the phenotype is not the result of one gene but the phenotype is the result of two or more genes u a bunch of different genes all contributing to the same phenotype now when the phenotype was only controlled by one gene we only had two options you know the flowers were either uh purple uh or white but when we have a bunch of different genes and they're all contributing to a single phenotype we get what's called continuous variation within the phenotype the best easily observable example of this is a lot of human traits in including skin tone there aren't just two options for hair color or skin color or eye color in humans there's a a whole spectrum of pale to dark and everything in between it's because this phenotype is not controlled by a single Gene it's controlled by a bunch of genes so continuous variation refers to the phenotype having a spectrum uh of different phenotypes uh of different possibilities the key terms Define continuous variation as an inheritance pattern in which a trait or phenotype shows a range of values and again just a call out one particular example skin tone and humans easy example of this this is a result of having multiple genes contribute to a single phenotype okay that's all I had for polygenic inheritance again going to be going through these there are several examples of non-mendelian inheritance uh another one is something called incomplete dominance so in incomplete dominance the heterozygote individuals are somewhere intermediate in appearance between the two homozygotes and again this is totally not what we talked about last time you know what we talked about with with classic mandelian genetics the heterozygote has the dominant phenotype it's not light purple it's not a mixture of purple and white in mandelian inheritance the uh heterozygous individual has the dominant phenotype but if we're talking about this uh incomplete dominance the heterozygotes are going to be a blend they're going to be somewhere in between this is really not very common uh these are Snapdragon flowers that do display this incomplete dominance and yeah you can see here's the red Al here's the white Al the heterozygote is pink it's it's in between red and white so um not that complicated to understand but it is a rarity in nature for sure incomplete dominance heterozygotes are somewhere in between the two homozygotes okay next we have something called co- dominance which I'll read the key terms definition now but it's exactly what it sounds like co-dominance um codominance is the complete and simultaneous expression of both alals in a heterozygote so this is not blending the two alals together code dominance is both alals are on and fully active and making their thing at the same time this is hard to wrap your brain around we will see an example of this in just a second because I I'm I'm going to do it two for one so I will show you an example of co-dominance uh but I will also show you an example of our next thing so just you know hold hold on to this for a second the idea of two uh different genotypes being expressed at the same time hold on to that idea there will be an example coming up um as we talk about multiple alals so this is another just example of non-m medallian inheritance you could have more than two so yeah in the in the first part of this chapter we had a purple Al and a white Al just those two options but Al are simply different versions of a gene there's nothing stopping them from being three or four or or or more than that multiple leals refers to a situation where there are just more than two uh there's a great example of this in humans uh our blood types so the blood types in humans are as the name implies uh three possible alals here the a Al the B Alo and the O Alo so three alal here in this system um o is recessive you know classically so just as we talked about recessive you know in the in mallan genetics uh a is dominant B is dominant and they are co-dominant with one another so yeah I told you this would be you know an example of co-dominance and an example of multiple alal so what does this actually look like well to understand this we have to look at what these blood types actually mean so the blood types refer to a specific protein present on the surface of our red blood cells if you have an a Al your red blood cells will have the a version of this protein on their surface if you have a b Al your red blood cells will have the B version of this protein on their surface here's the co-dominance if you have an A Al and a b Al if you've got a B typee blood it's pretty rare in in uh in our population but if you've got AB type blood there's the co-dominance you are making the a version of this protein and the B version of this protein on the surface of your red blood cells so that's how we can have both alal expressing themselves at the same time that's the co-dominance uh and the O alil is defective um if you have an O alil it doesn't make any version of this particular protein on the surface of the red blood cells and so if we want to make a little table for this um again with with three alals there are more than just two possible genotypes um these are all the possible genotypes and phenotypes um it's easy to fill out you know instead of having to just memorize this table but yeah if you've got uh an A alil and another a alil of course you're going to have a type blood uh if you've got an A alil and an O Al remember o is recessive so if uh you've got one gene saying make the a version and another Gene saying I don't know what to make you're going to make a version you know the the just like we saw with purple and white a defective Al here doesn't do anything but it doesn't get in the way of any other alals that may be there so a alil and o alil results in a type blood a b Al and another B alil obviously you're going to have B type blood if you've got a alal and an O alal just like we said here o is recessive you're going to have B type blood uh if you've got an O alal and another o alal you're going to have this recessive phenotype you're going to have O type blood and then here's the co-dominance if you've got an A alal and A B you're going to have AB type blood so interestingly if you have O type blood um by the way if you don't know your blood type I know the uh Life share is a blood donation place that has um trucks that come by campus often enough if if they're ever on campus and you see those uh and you're you know healthwise you're able to donate blood that's always a good thing to do they always need blood for people uh in in hospitals uh but as a fringe benefit to you uh if you donate blood with them uh you get a little account and a little card and everything and uh they'll tell you important information about your health uh your you know blood pressure and cholesterol levels and and your blood type so if you don't know your blood type you can donate blood and you'll know your blood type uh if you've got ootype blood that's your phenotype you actually know your genotype you know exactly which genes you have because there's only one way to have O type blood same thing with a B if you've got AB type blood you know exactly which alals you have for this Gene uh however if you've got a type blood you don't necessarily know you could be AA or you could be AO if you've got B type blood it could be bb or or it could be bo so um yeah in interesting interesting to look at uh very applicable to to humans and stuff and yeah donate donate blood if you're if you're able to um one last thing about blood just CU in class someone usually asks about this um they ask why this matters the short version is uh your immune system freaks out against proteins it is not familiar with so if you've got a type blood your immune system system is you know used to seeing the a version but if you've got a type blood and you are transfused with uh B versions your body is going to attack that and it's going to it's going to be bad uh yeah and if if you've got B type blood you're used to the B protein but if you're given either of these types your body's going to have a negative reaction against it O type blood your body is going to freak out against any of this stuff but you'll be fine with receiving other O type blood this also means O type blood cuz it doesn't have any copies of this protein any version of this protein uh anyone can accept O type blood so if you have uh O type blood and you know you've got it uh it is even more important for you to to donate blood if you are able to when you are able to uh because yeah it's sort of the universal donor it's sometimes called because yeah a can accept O type blood there's nothing to offend them here B can accept O type blood there's nothing that's going to trigger an immune response AB can accept O type blood there's nothing here that they'll react against then of course o can you know receive O type blood as well so uh anyway I'm not writing any of that down there's just usually several people who are curious about why this matters it has to do with immune reactions and reacting against things that you're not familiar with with proteins you're not familiar with okay what's our next example so again still still under this umbrella of non-mendelian inheritance let's talk about something called recessive lethal this refers to an Al that is is lethal deadly but only when you have two of it uh if you're heterozygous for this lethal alal it's not lethal uh there may be a phenotype associated with it there may not be a phenotype associated with it but it's not lethal in its heterozygous form this alal is lethal in its homozygous form example more cats here's a mans cat so this is a cat that does not have a tail or has an incredible short tail uh it's due to this defective stub tail Gene if you follow this up here the healthy alil is the lower case the uh you know stub tail Gene is the the uppercase uh the capital again s not a letter I would choose uh especially if you're doing handwriting here s is very confusable but again stub tail s that's why they picked s so yeah here's the heterozygous individual with only one copy of this recessive lethal alil and yeah it's it's it's alive it has a phenotype it has a stud tail but it's not dead uh and yeah this is kind of showing a punet square so one stub parent and another stub parent you know one heterozygote crossed with another heterozygote these are our possible Offspring normal tail stub tail stub tail here's The lethality so recessive lethal it is lethal when you have two copies of it so here's stub tail Le and a second stub tail alil this is catastrophic to growth and development this is going to be lethal to the embryo early on dead but again in its heterozygous form not Lethal lethal in homozygous so yep lethal in homozygous in heterozygous may have a phenotype or may not have a phenotype and yeah the example here is the MS cat embryonic lethal to the in the homozygote heterozygote has a simply a stud tail all right next we've got something called XL traits xlink traits are where the gene for this trait is located on the X chromosome now at this point we need to do a bit of a sidebar so you could note this in in your notes however you want to I'm doing this here we have to go on a bit of a side tangent so we understand what an X chromosome actually is then we'll come back to xlent traits so most most mammals including ourselves use this XY system for biological sex determination so we only have one sex chromosome the X and the Y are two different versions of that sex chromosome so these are kind of like Al uh Al are two different versions of a given Gene X and Y are two different versions of an entire chromosome so we have two different vers versions of this chromosome and yep don't sweat the details here but yeah here's an X chromosome uh it's rather large compared to everything else it has a lot of important genes uh here's the Y chromosome uh it is much much much smaller we'll see why in just a second uh but yeah these are two different versions of the sex chromosome and we saw this uh yeah coming back to this for like what the third time uh eukariotic chromosomes yeah two cies of chromosome 1 two copies of chromosome 2 two copies of chromosome 3 if we skip down there's the 23rd chromosome the sex chromosome uh it looks like this individual has an X and another x uh but yeah we've got two copies of the sex chromosome um side note to the sidebar um so this these are the sex chromosomes everything else is called an autosome so all other chromosomes other than the sex chromosomes are called autosomes they're not directly involved in sexual development so what what is the difference between these two so we got two different versions what do they do well the X chromosome is involved in sex development but it's also just required for life there's a ton of genes among these you know thousand genes on the on the X chromosome that you just need to live we cannot live without an X chromos so it the X chromosome has many genes not related to sex development that are just straight up required to be alive and the other genes within the X chromosome direct development toward female sex it just has instructions for you know during development uh build build uterus build ovaries like go through this process of building female sex the Y chromosome does not have genes that are required for life again it is much smaller than the X chromosome it doesn't have anything that we that we strictly need uh so yeah you can survive without a y chromosome about half the people on the planet are surviving just fine without a y chromosome uh Y chromosome is not required for life and what it does is it in some ways just Alters the ex instructions uh to lead to male sex oh don't build ovaries build testes instead so it's sort of taking for granted that anyone with a Y chromosome also has an X chromosome because everyone has an X chromosome because it's required for life that's why the Y chromosome is much smaller it's just taking the instructions of the X and changing them a little bit leading to male sex so again we are we are diploid we have two copies of each chromosome so our possibilities here are an X chromosome and another X chromosome the instructions here are going to lead to the the development of female sex uh if you have an X chromosome and a y chromosome the instructions here especially on this y are going to change things lead to the development of male sex um if you're looking at the possible combinations here yeah what about why why well this is not normally possible with the way eggs and sperm work and even if it were possible and you were to create a cell that had a y chromosome and another Y chromosome it would not be viable remember the X chromosome has genes that are required for life so any cell that had two Y chromosomes and no X chromosome at all uh would would not be able to survive that would be that would be lethal to development um one other thing in this sidebar is uh this is not the only way to do things so you know in in humans and most mammals and oddly enough in fruit flies as well uh there is this XY system females have two of the same thing males have one of each uh but in birds for example it's the exact opposite in Birds males have two of the same sex chromosome and it's females that have two different ones when we get to invertebrates it gets even wackier uh with just different numbers of chromosomes and things like Grasshoppers and honeybees are really weird the males are just straight up hloy uh there's no dedicated sex chromosomes just every single chromosome the males only have one of and the females are are diploid and have two two of so uh don't memorize this table but it is interesting to look at my point here in other animals uh you know other than mammals other than humans sex can be determined through different mechanisms and even not on this list not even listed on this table there are many reptiles that determine sex not using genetics at all um there are many crocodilians that determine male female sex based on the temperature of the eggs as they're developing so yeah there are other ways to do this the XY is is just how mammals do this so end of sidebar all of this uh was trying to explain what XL trait is supposed to mean so an XL trait is a trait where this Gene you know for this for this phenotype for this trait is located on the X chromosome this matters because XY individuals Only Have One X X chromosome you know for every other Gene we are diploid we have two copies you know it matters whether it's dominant or recessive but if you're XY if you only have one X chromosome there is no backup copy it doesn't matter whether it's dominant or recessive you get what you get there's only one of these that you have so if this is a a disease uh Associated um with the X chromosome XY individual uals are going to be more likely to have this because they only have one copy of that Gene they don't have a backup um red green color blindness is an example of this um I I can't verify this but I guess if you're red green color blind these two sets of these two images should look exactly the same um but red green color blindness again nothing to do with sex development at all uh the genes for this are on the X chromosome so um if you're XY and you've got one defective copy you're going to be red green color blind it is possible for XX individuals to be red green color blind but they would have to have two defective copies it's just more difficult for that to happen uh so yeah this is what I mean XY individuals are more likely to have these XL traits uh duchaine muscular distrophy and uh skid X1 it's a severe immune system disorder uh those are ALS so xlink traits and are much more commonly seen uh in XY individuals okay one one more one more example of non-mendelian inheritance this is kind of a a big one but I I think it's a pretty interesting one uh it is something called epistasis now it's highlighted it's in the key terms but I actually don't want to start by reading the key terms definition I want to you know walk through this process and then we'll read the key terms definition so uh an example of epistasis is coat color in mice so let look at these mes we got three options we've got a goodie okay it's it's brown uh I don't know why M People call this a gie but it's it's a goody also known as brown we've got black we've got white also known as albino now there are two genes involved in determining what the coat color of the mouse is aha you may say that's polygenic inheritance well it kind of is polygenic inheritance this is you know two or more genes contributing to to the phenotype but as we will see epistasis and what's going on with these mice is not just two or more genes it's a little more complicated than that so one of these genes controls what the color of the pigment is so the Audi or brown uh the Audi alil is dominant and hey capital A it works this time but yeah the the uh the letter we choose is usually associated with a dominant phenotype so the capital A alil the the Audi or brown is dominant the black again not B these are the same gene they're two different versions of the gene uh the black Al lowercase a is recessive so yeah Brown is dominant black is recessive that is one gene controlling what the color of the pigment is going to be there is a separate Gene a second Gene that controls whether the pigment is actually made or not normal production capital c not sure why it's C whatever uh is dominant but no pigment being produced which results in in albino phenotype that is recessive that is lowercase C the reason why this is not just polygenic is because among these two genes one controlling the color of the pigment and one controlling whether the pigment is produced or not this Gene overrides this Gene the pigment production Gene is sort of stronger than the pigment color Gene it doesn't matter what the pigment color Gene is saying this is going to sort of take precedent over it let's look at how this can play out so this is essentially a massive Punit Square tracking these two genes don't memorize you know the exact numbers or percentages here let's just look at all the possible combinations of mice so let's focus on the a gene first capital a capital A it's brown it's a goody duh uh heterozygous you know capital a lowercase a remember a gy is dominant and black is recessive so heterozygotes are going to be brown capital a capital a brown capital a lowercase a brown capital a lower case a brown I mean all all these things are brown to look at some black mice yeah lower case a lower case a black it's the recessive phenotype the only way to have the recessive phenotype is to be homozygous recessive there's another homozygous recessive there's another homozygous recessive all right let's start paying attention to the C alals remember capital c means normal pigment production so Capital C capital c that means okay other Gene go ahead do your thing in this case Brown Capital C Capital C okay other Gene do your thing in this case Brown here's Capital C lowercase C again normal pigment production is dominant no pigment production or albino is recessive so being heterozygous for this pigment production Gene means yep go ahead first Gene do your thing in this case resulting in a guty and we see this here in the black mice Capital C Capital C yep go ahead and have black pigment Capital C lowercase C yep go ahead have black pigment but let's look at these lowercase C lowercase C that means no pigment this is supposed to be in ay Mouse according to this Gene but because this pigment production Gene overrides the effects of this first Gene it's going to be albino no pigment production doesn't matter what the a gene is saying here's another a goody mouse that is now albino because of lowercase C lowercase C here's a black mouse or it's supposed to be making black pigment but that black pigment is overridden by the lowercase C lowercase C so epistasis is not just two different Al or multiple alals it is multiple genes where one is stronger than the other so let me read the key terms definition of epistasis here the key terms define this as an antagonistic interaction between genes such that one gene masks or interferes with the expression of another we see this here with the pigment production Gene the C Gene masking the effects or interfering with the effects of this first Gene the black or Audy pigment so uh again we had it written down before in summary yeah the the lowercase C lowercase C mice are white regardless of what the Audi black alals say this Gene overrides the the other Gene okay that brings us to the end of Mandel non- mandelian inheritance and to the end of genetics but we're actually not done with this recorded lecture with the last few minutes I want to skip over and briefly get started on the next chapter chapter 14 DNA structure and function to understand the topics in this chapter we're going to need some background about DNA and actually we've kind of done this already but remember my class is not supposed to be cumulative so even though I talked about this sort of stuff on exam number one uh I'm not going to test you over it again unless I bring it up again so everything I'm bringing up again here uh is fair game for this exam as well we really need a refresher about a lot of this stuff in order to understand this chapter on how DNA works so let's start with this statement DNA is made of nucleotides DNA is a polymer of nucleotides a bunch of these individual structures uh that are put together uh phosphate um five carbon sugar here nitrogenous base um not uracil that's RNA only DNA can have adenine guanine thyine or cytosine so to summarize nucleotides consist of a five carbon sugar a a negatively charged phosphate group and a nitrogenous base which could be adenine a guanine G cytosine c or thyine t no osell that's an RNA thing the five Prime phosphate of one nucleotide is connected to the three prime o of the next in a phosphodiester bond this should look familiar to you and uh yep there is the five Prime phosphate connected to the thre Prime o five Prime phosphate connected to three prime o here's a five Prime phosphate and if we were to continue building this strand of DNA there would be a thre Prime o of a nucleotide that would come in here and become attached to this five Prime phosphate again these terms five Prime and three prime going to be very important as we go through this chapter the five Prime end has the phosphate the three prime end has the O they're always connected to one another in this way now we don't just have one strand we've got two there are two strands of DNA that form a double helix structure the U Integrity of this double helix is held together by hydrogen bonds between these bases so two strands of DNA form a double helix held together by H bonds between the bases in a very specific way thyine Partners up with Adine guanine Partners up with cytosine if you hadn't drilled this into your brain already in the earlier chapter here it is again these are the rules for base complementarity C pairs with g a pairs with t that is how they optimize the strength of their hydrogen bonds any strand of DNA is going to have a nucleotide opposite it you know according to these rules C's are partnered up with G's A's are partnered up with T's now all of this so far should be familiar should be review from you know several chapters ago there is one new thing that I want to introduce now that will be very important when we talk about the rest of the stuff in this chapter and it has once again to do with the the five Prime and three prime stuff so uh however long this strand is doesn't matter whether it's three nucleotides long or 3 million nucleotides long if it's a line of nucle tiddes there's always going to be one end with a free phosphate not attached to any partner and the other end is going to be a free thre Prime o not attached to any phosphate partner we can see these things labeled on lots of these figures here so Circle this yeah here is the three prime end of this long string this is the five Prime end of this long string and uh yep here's a more detailed view of it but yeah here's the five Prime phosphate that is free it's the very end of this DNA molecule here's the thre Prime end down here the O that's that doesn't have any partner uh yeah doesn't matter how long it is any strand of DNA is going to have a five Prime end and a thre Prime end now the important thing the other important thing is that in a DNA double helix these two strands of DNA do not go in the same direction they're pointed in opposite directions so notice here the Strand on the left it just happens to be drawn so the three prime is at the top and the five Prime is at the bottom the other strand is going to be opposite it's five Prime is at the top it's three prime is at the bottom we see this over here in the more detailed one as well the one on the left is running five Prime to three prime the Strand on the right is running five Prime from the bottom to the three prime at the top two strands of DNA in the double helix run again the technical term is not opposite the technical term is anti-parallel they run anti-parallel to one another they're going five Prime to three prime but in opposite directions um we can actually kind of draw this ourselves if you want to draw p piece of DNA I I I am not a great artist which is why I rely on you know great figures like this but for some things I can draw this myself even if I were writing on paper I can draw two lines there there's my DNA if we wanted to label this um let's say this top strand has five Prime on the left and three Prime on the right because the two strands are always anti-parallel to one another if we were to label the bottom strand here the bottom strand would be labeled like this three Prime on the left five Prime on the right again get comfortable with five Prime three prime and get comfortable with the idea of them running in opposite directions we're going to see a lot of five Prime three prime stuff uh as we get deeper into this chapter uh speaking of which yeah we'll get deeper into this chapter in the next recorded lecture I I just briefly wanted to get started on DNA structure function in this recorded lecture so that we could really start things in Earnest in the next one so this is the end of recorded lecture 34