[Music] hi it's Mr Anderson and welcome to biology Essentials video 29 this is on mendelian genetics and it's called melan genetics it's named after Gregor mendle um in biology there are two famous names Darwin who was famous and controversial in his own time and Gregor mendle who died in obscurity but both of them made huge advances in the field of of biology and Gregor mle in the area of genetics uh if they could have gotten together those two theories when they finally came together as modern Sy synthesis it was really powerful unfortunately he dies in obscurity but this is what he did he was crossing pea plants and so he can take one PE plant and you use a paintbrush to transfer pollen from one to another so you know who are the parents he would then create Offspring as a result of that now pe's are great because they have a number of different characteristics and more importantly you can make a lot of them really quickly so in a pod each of these keas is an actual new organism so you can plant those and see how they grow and so he figured out a lot of genetics as a as a result of that and so genetics in this podcast I'll talk about our mandelian or simple genetics um he identified the Gene and he came up with two laws the law of segregation and independent assortment I'll talk about those we'll also have some problems so I'll have some practice problems that you can try and I'll show you how to work those out and we'll finish with genetic disorders the example I'll talk about is hunting s disease and with genetic testing it opens up this whole idea of ethics and privacy now what won't I be talking about I won't be talking about link genes in other words if genes are ever on the same chromosome or on a sex chromosome or or caused by multi- genes gets really complex and so I'll talk about those in the next podcast on Advanced genetics um but know this that simple mandelian genetics the rules are simple rules of math rules of probability and if you understand those and how to do uh the first cross that I show you um you should do well in in most any of the crosses you get in genetics so this is what mendal did he crossed purple flowers with white flowers and he got purple flowers now a few things that you should know uh the first cross in any genetic cross is called the P Cross or the parental cross and then The Offspring of that are called the F1 or the filial one or The Offspring of that cross and so at the time of mendal everybody believed in this idea of blending that if you if you cross two parents so Mom and Dad their kids look a lot like them and so it's maybe a blending of all some they didn't know that they were jeans but something inside of them and so when he crossed purple with white and got purple flowers that made total sense back then um this is kind of fits in this blending but what he did next was he crossed these purple flowers with themselves and what he got was a 3:1 ratio of purple to White and that white returned just as Crystal white as as that first White was to begin with and so what he said is that there's a character a trait that's passed through here but we now identify that as a gene that's carried uh distinctly through each of those generations and then shows up again now if you know anything about genetics you'd know that in simple mandelian genetics it looks like purple is dominant white is recessive but we know that because of the work of mendal and so this is what the second cross is the one that was puzzling and this is what he figured out so these Offspring right here were hybrid for the trait and so if we look at the parents the parents would be big p big p that represents one purple flower Little P Little P represents the white flower and so each of these would be big p Little P and so you can use a punet square a punet square you put the pollen or the male here the female right here and each of these genes get a certain column and so this would be one parent big p Little P and so you simply write that across so we got big p and Little P here we got big p and Little P here so this represents the two different parents Crossing with each other and then we simply figure out what comes so here's big p big p so we get a big p from one a big p from the other so that'd be big p big p since P big p is dominant we get a purple flower on the next one I'm going to take a big p from here a little P from here and so that would be still purple because this this one is a dominant a or a dominant gene down here we get a big p from here and a little P from here and so that's purple and the reason we get white flowers is that you get a little P from both of the parents and so the neat thing about a punet square and that's what this is is it not only allows you to quickly do the probability but it shows you the percent we should get in those Offspring in other words three of them should be purple and one of them should be white so we should have a 3 to one ratio and if you ever get a cross like this in a problem for example cross like this just if you're not sure what are The Offspring are going to be just do a simple punet Square uh where these two Al or versions of the gene are going to be on the top and these two are going to be on the side and we'll do some practice problems in just a second and so what are mle's laws well the two things that he figured out are the uh law one mle's law one it's called the law of segregation and mle's law two is the Law of Independent Assortment and so let's start with law one and so if we ever and I've got a coin here because the the the actual way you get genes are almost like a coin flip so if you think about a coin it has heads on one side and Tails on the other when you flip a coin what are the odds that you're going to get heads or tails well it's a one and two probability that you'll get heads same thing with genes and so if this is that F1 generation and this shouldn't be B this should be p so we'd say this is uh big p Little P what are the odds that the offspring are going to get a big p well it's a one and two what are the odds that they're going to get a little p it's one and two and so that separation of those two alals is called segregation and so this idea of segregation says that there's a 50% chance you're going to get either of these genes and so that's segregation they separate and it's just random chance the next one is the law of independent assort Law of Independent Assortment says that um this Gene the gene that causes for example hitchhiker's thumb which is where your thumb actually bends back and the gene that causes an attached earlobe so right here I've got a free earlobe um those two traits don't affect each other in other words they sort independently and so we can work problems without mixing these two together they're going to not influence one another now sometimes we find for example that some things do travel together so you'll notice that people who have red hair also have freckles and that's because those two genes are actually found on the same chromosome and so they seem to travel together and so we're not going to deal with link genes again we'll do that later and so independent assortment means that traits don't affect each other and so what I'm going to do next is I'm going to leave this for a second these are six problems that I'll work through but if you want to work these you could pause the video at this point and then then you can come back and and uh uh start the video again and see me work through each of these so I'll pause all right so let me go through these question one a coin is flipped four times comes up heads each time what is the probability that the next coin flip will come up heads well everything that's happened in the past can't influence anything that's going to come in the future and so it's a one half probability that you'll get heads in other words you could have 10 kids they could all be boys what are the odds that the next one going to be a a girl it's still a one and two probability let's look at the next one and so we've got some things up here round P's are going to be Big R and wrinkled P's are going to be um little r yellow will be Big Y and dominant is going to be or uh green is going to be little y generally whatever is the dominant trait we give that the capital letter in this case round gets the Big R and yellow gets the Big Y and so question number two classify the following as heterozygous or homozygous heterozygous means you have different genes or different Al homozygous means you have the same and so this first one Big R Big R would be homozygous dominant they have the same this would be heterozygous and we also sometimes refer to that as hybrid the next one would be homozygous recessive and the next one would be homo or excuse me heterozygous yellow homozygous for the round um so it's going to be heterozygous and then homozygous dominant on the next one so so that tells you the AL that you have let's look at number three what's the phenotype of the following well this right here is going to be the genotype in other words Big Y little Y is going to be the genes that you have what's going to be the phenotype well that's physically what you look like and so for the first one this one right here even though it's genotype is Big Y little y or it's heterozygous for that it's phenotype would be yellow so this is going to be yellow this one's going to be round this one's going to be uh green and this one here is going to be yellow round phenotype is physically what you look like let's look at the next one number four what's the probability of this cross so we have two round seeds producing wrinkled seeds well like I said before if you ever get one of these it's a simple monohybrid cross I would always do a punet square and so we put big r and little r on one side of my ponet square Big R little r on the other side of my ponent square so what are the odds that I'm going to get wrinkled seeds well there's a little r here a little r here and so there would be a one in four probability that we'd have wrinkled seeds because this one's going to be round this one's going to be round this one's going to be round as well and so again if you ever get a simple cross like that do a upon it Square let's look at the next one what's the probability that this cross would produce green seeds well I do the same thing again Big Y little y crossed with little y little Y and we're looking for green seeds green seeds remember are going to be little y little Y and so I could get it here I could get it here and so that is a two and four or a one and two probability that we're going to get green seeds from that and so even though you might think you're super smart do a pun it Square you're you're never going to miss the problem then now this is a problem that we'll sometimes get on the AP bio test as well if these parents are crossed together what are the odds that you'd get that well to do this one you'd have to actually set up a pretty intense Punit square and so if you get one like this don't do a 4x4 Punit Square just work each of them individually and so what do I mean by that well let's start on the on the RS what are the odds that if you produce this and that you could get that so let's do an RS first so Big R little r crossed with Big R Big R what are the odds that we're going to get Big R little r well neither of these but this is a Big R little r this is a Big R little r and so the odds of these two parents producing these Offspring is going to be a one and two probability so I'm going to write that right over here underneath the one and two probability now let's work the Y's so let me get a different color so if we do the Y's what are the odds that these two parents are going to produce that Offspring well let's do those together so here are the parents Big Y little y crossed with Big Y little y so this is going to be Big Y Big Y little y little y Big Y little y Big Y little y so what are the odds that we're going to produce again Big Y little y well it's a two and four or a one and two probability so I'm going to write one and two here okay so now instead of doing this huge unwieldy 4x4 Punit Square what I've done is I've almost got there because the odds of getting this are 1 and two the odds of getting this are one and two so what are the odds of getting both of those I simply multiply those together and it's a one and four in other words what are the odds of rolling one or flipping the coin and getting heads one/ half what are the odds of flipping two heads in a row it's a half times a half or a fourth and so you can solve problems like this just using What's called the law of multiplication when these two things have to happen so I hope you did well on those problems last thing I want to talk about is disease and and a nasty disease is called hunting sin's disease it's named after the person who identified in the 1800s but essentially what you get is degeneration of the nerve fibers in this portion of your brain and so what happens is eventually you start to get um uncontrollable shakes you can't really walk eventually you die as a result of that now the problem with Huntington's disease is you don't know you have it until you're middleaged so I could have Huntington dis disease right now I'm going to die as a result of this disease but I don't know it and so I've already had kids I've already passed the genes on a famous person who had Huntington's disease is this guy his name is Woody Guthrie you probably know him he wrote the the song This Land Is Your Land This land is my land um and he died as a result of having Huntington's disease now it's a dominant trait in other words if you are this you get Huntington's disease if you are this you don't and so let's look at a p pedigree a pedigree shows you how a disease can be passed down through uh organisms and so on a pedigree a square is I is going to be a male a circle is going to be a female and if you ever have a horizontal line between them it means that they had Offspring and so this is a uh the grandparents in this case and they had a boy and then the next person kid they had was a boy and then they had a girl and then they had another girl and you can see that these this girl for example had her own family but you can trace the disease through it in other words since this parent right here is Big let's use a different color Big H little H and this one is little H little H this big H was actually transferred to the sun it was not transferred to this sun it was not transferred to this daughter but it was transferred to this daughter over here and so the odds of passing it on are one and two and you can see that one and two of their kids had that and if it's a dominant disease like this lots of times we'll see it in generation after generation after generation but you've reproduced already by that time and so um it's almost too late now where does this become an Ethics issue well we now have a test for Huntington's disease and so Woody Guth Woody Guthry had a number of kids one of those is named Arlo Guthrie who's also a famous H folk singer and so Arlo Guthrie may have the Huntington's Gene he has a one and two probability of getting it we now have a test that can figure out if you have that Gene but it'll influence your life in the future and so would you want to know that you're going to get a disease that will cause a nasty death as a result of that there's not a lot of treatment for hunting disease or not and would your insurance company want to know that as well and so again the the the genetics behind uh simple mandelian genetics are fairly simple but it opens up all these moral issues and I don't have an answer for any of those questions but it's something we're going to have to deal with in the future and so that's genetics mandelian genetics and I hope that's helpful