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our lecture for today is about genetics which is chapter 10 in your textbook and let's start by recalling we just finished with meiosis which is the process of essentially halving or cutting in half the genetic material so that we would have a haploid sperm and a haploid egg and when the sperm and egg fuse then the first cell that we have is called the zygote and this zygote now is a diploid cell because it has half of its genetic material from the sperm and
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half from the egg. So, in every cell that follows that they're going to be diploid cells in that organism and the chromosomes will always be paired. And by paired what I mean is for each of the chromosomes in the organism for for us we have 23 pair of chromosomes one of those pair we inherited from our mom and one we inherited from our Father. Now we call those pairs homologous pairs because they share the same genes. Now they may not be the exact same forms of
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the genes they may be different forms that they are the same genes now when we have different forms of a gene we call that an allele. So, for example if we talk about a particular protein that either gives light eyes or dark eyes then if you have that particular protein if you have the dominant form of that protein that would be one form so that would be one allele or if you have the recessive form of that protein that would be another type or another allele for that particular gene.
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So we talked about when these haploid cells fused we get this diploid zygote and so if you look down here this is what the haploid cell would look like. Let's say that the larger chromosome represents chromosome 1 and the smaller chromosome represents chromosome 2. In the haploid cell we don't have two copies of each we have only one but in the diploid cell we now have our homologous pairs for each of the chromosomes so we see we have a pair of
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chromosome ones that are represented in blue and pink and then we have a pair of chromosome 2 representing the blue and the pink up here at the top of the karyotype which we've talked about that just where the chromosomes all 23 pair have been ordered by their homologous pairs and the only exception to that would be the sex cell - the sex chromosome excuse me where if you're a female then your chromosomes are going to be XX but if you're a male you're
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going to have XY so that would be one area where we have an exception to that. So if we look down here at our homologous chromosome pairs we see that there are three different genes that are represented on these chromosomes and so if we look at gene a we can see that both the maternal and the paternal types or forms of gene a are the same so they have the same allele or form of that gene but if we look at gene b we see that over here the maternal chromosome
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has the dominant form the capital B that allele for that gene whereas the paternal copy has the lowercase the recessive form of the genes so in a diploid organism every talk through today it's important to remember that we get two copies for every gene because we've inherited one for mom and one from dad that's what makes us a diploid organism
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so let's move a little bit and talk about Mindell he was a a geneticist who studied traits how they are inherited so we didn't have the word gene back then he didn't understand that but he did understand that there was something going on something that was passed from one generation to the next and so he studied these traits using Pea plants and what he did is he was able to hand pollinate these to control what plants were breeding with other plans or self
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pollinating and so in a pea plant if you look here at this pea pod every single one of these becomes a seed therefore is an individual so each one of these is an offspring from this cross so we see here we started with a tall plant and a short plant and so there was a cross done where the pollen from the tall plant was painted on or transferred to the shorter plant and then we have resulting seeds from this cross so each of these seeds is planted and each one
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will actually become a plant of its own and so we see that we have a tall plant a short plant tall plant tall plant and a short plant from from that particular cross and so part of Mendel's work was to plant to do these crosses plant the seeds and count the number of offspring that had each of the traits whether it was tall or whether it was short now here are some examples of traits that he studied and he counted up the offspring for and so we have over here either
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around or a wrinkled feed and then we have either a yellow or a green seed white or purple flowers smooth or wrinkled ods yellow or green pods axial or Terminal flowers and then the tall and short plant so all of these listed here were determined to be what we called the dominant form of the trait and these down below were found to be the recessive form of the trade now it's important for us to talk about the difference between phenotype and genotype the phenotype is simply the
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physical appearance and so we know that this is based on the proteins that are produced in an organism so all of this chart is showing the different phenotypes that are possible for all of these traits the genotype this is actually the genes right so this is the form of the gene or the type of allele and the gene is what gives the instructions okay so that you get this physical appearance the game is the instructions for the phenotype
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now in this particular slide what we have is an example of what's called a true breeding plant and a hybrid plant true breeding simply means when you self pollinate that plant so the plant is serving as both parents every time you do that you're going to get the same phenotype and so if we have a green seed and it is self-pollinated every time we are going to get only green seeds that would be a true breeding plant everything is the same as a parent same
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thing here we have a yellow feed self-pollinated and we get only yellow seeds same as a parent those would both be true breeding now we know that the yellow is actually the dominant form for this particular trait and the green is actually the recessive form we'll talk about that a little more in just a second in this case though we have a yellow seed and it's the plant self pollinate but rather than getting all yellow seeds we get a mixture we get
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yellow but we also get green this would be called a hybrid because it gives us a mixture and it doesn't give us the same result as the parent
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so let's talk for just a second about dominant versus recessive okay a dominant allele or the dominant form of a gene really just means that if its present it masks the recessive or covers up this is the one you're going to see is the dominant one okay so if there is a dominant form present you will see the phenotype of that particular dominant trait okay the recessive can be masked by the dominant allele so if you have the presence of a dominant allele that's
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the that's the physical trait you're going to see not the recessive one so let us sign and some letters that represent the gene for more the allele for these particular traits and so we know that yellow in this case is the dominant form so let's use always with dominant we're going to use a capital letter so we use the capital y to represent the dominant form which in this case is yellow and then the recessive allele we use the same letter
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choice so we're still going to use the y but we're going to use a lowercase Y because that always represents the recessive allele so the recessive allele then yields a phenotype the green phenotype so in this case we have two parents we have a green seeded parent and we have a yellow seated parent the green seated parent we know what the genotype is since since the green is the recessive phenotype there's only one way that a plant can be green to you then
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that is little Y little Y because if there was a big y present that would mask over the recessive form and it would be yellow so we know the genotype of dis parent is little by little line now this parent we know has at least one big y because the phenotype is yellow but this could be a yellow seated plant and be big why Big Y or Big Y little Y so what we have to do if you have to look at the offspring to determine whether or not
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this parent is the big y big lie or big my little why and if we look in this case we have all yellow seeds which tells us that this is in fact the we call it homozygous dominant we're going to talk about that on the next slide
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form homozygous meaning two of the same dominant meaning the dominant allele so big why big why is the homozygous dominant form for this particular trait now let's look at this next example again to be green seated there's only one way because Green is the recessive form so it has to be a little while little why and if you look at the offspring here we see that some are yellow and some are green meaning this particular parent had to be Big Y little
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Y now let's talk through on the next slide how did mendel determine that and how are we going to be able to determine and things like this so as I mentioned to you homozygous dominant would be the yellow form where we have two of the dominant alleles in this case they're using GE as their representation we used why the letter is not important they use G for green we use Y for yellow so big why big y would be the homozygous dominant foreign if we chose to use Y as
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our letter of representation heterozygous means one is each so in this case it would be Big Y little Y it's still going to have the seeing a type of yellow because as long as there is one dominant form of a gene or one dominant allele that is the phenotype that's going to be visible that's because it's going to mask over the recessive allele and in our last example remember homozygous meaning two of the same and so two recessive is what
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is the same so in our example this would be little my little wine this is the only way that you're going to see the recessive phenotype otherwise the if there is a dominant little present at all then you'll see the yellow phenotype a punnett square is what we'll use and in this case we're talking only about one trait so where it's a one trait cross and as we go further in the chapter we'll talk about to trade crosses and some other examples that
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aren't completely dominant and recessive but let's just look at a punnett square for a second what is the purpose of a punnett square the purpose is to give us an idea of what the genetics of the offsprings might be okay so it's a it's predicting or the probability of what the offspring genetics will be in order to set up a punnett square what you're doing is you're saying what are the possible gametes remember gametes would be sperm and eggs right from the parents
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so what are the possible gametes that each parent can produce and then what are all the possible combinations of the gimmies so if we start here at this this is going to be our female parent and the genotype of the female parent is big G little G so this is a heterozygous parent because we have one dominant and one recessive so the phenotype is yellow the dominant phenotype because it has one of the dominant alleles the male parent has the same genotype big G
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little G also heterozygous and what you'll do when you're producing the gametes for the punnett square remember that the game each occur after meiosis and so we have to take the genetics and we have to cut it in half so we say okay there are two alleles here but each gamete would only have one allele so one of the alleles is going to be present in one game meet the other allele will be present in a separate gammy because we have to have
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half of our genetic material in the gametes so this female parent can basically make two types of gametes one game for this gene one game II will be the dominant allele and one will be the recessive allele we have the same exact possibilities for the male one gamete will be the dominant allele and the other game meat will be the recessive which gametes are going to be the ones that actually are fertilized and produced the zygote we don't know so
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we're just predicting what are all possible outcomes and how likely are they so once you've set up your gametes which are go across the top right and the side of your punnett square and in this case we're only doing a one trait cross we're looking at one trait at a time which is a four box punnett square so at this point you're going to when you fill it in this cami will fill in here and down this game eat will fill in here and across and this one fills in
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here and down and this one fills in here and across and when you when you fill them all in you can see they've color-coded it for us so we can easily see the phenotype but we have the punnett square tells us first the genetic or the genotypic ratio and then we can figure out the phenotypic ratio based on that so in this case our genotypic ratio we have one the homozygous dominant one big G big G that's a true breeding yellow seeded
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planet then we have two heterozygous offspring big G little G these still going to be yellow but they are not homozygous dominant and then we have one of the homozygous recessive which is little g rosary this will be the only green ste did plant now when we look at the genotypic ratio then we can also determine our phenotypic ratio so the phenotype were not worried about letters anymore or genes were worried about the actual physical appearance so out of
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these three out of the four are going to be yellow and the fourth one is going to be green so make sure when you're doing your genotypic and phenotypic ratio that you're keeping those straight which one is the color the physical appearance in which one is the genes so we see here if we cross a yellow seed plant if we don't know the genotypes okay so a yellow stated plant could either be big G big G or big G little G and we cross a green seeded plant well there's only one way
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to be green seeded in that little G little G because Green is the recessive phenotype if the cross yields all yellow seeds then you are going to be able to determine that the yellow seated parent is in fact homozygous dominant so we figure that out by setting up the punnett square so the male we know is the same there's no way the male could be green and have any other genotype so what we're looking at is a female form if it's homozygous dominant what will
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the offspring look like vs if the female is heterozygous so the females homozygous dominant there's only one type of gamete she can have she can only produce the dominant game eat and when you fill in this punnett square you see that one hundred percent of them are going to be big G little G which means they'll be all be yellow down here we have a dominant allele and a recessive allele so we have gametes that can have either right now obviously the male
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gametes are going to have the recessive when you fill that punnett square and you see that fifty percent of them are big G little G and fifty percent our little G little G which means you have fifty percent yellow and fifty percent green now I want to go back and show you one other thing on this particular cross we call this a mono hybrid cross because both parents are hybrids right heterozygous it's one trait so it's only one trade so when both parents are
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hybrids and it's a one trait cross then it's called a monohybrid cross and in every monohybrid cost you're going to have the same genotypic ratio and the same phenotypic ratio the genotypic ratio will always be one of the homozygote dominance to two of the heterozygous to one of the homozygous recessive and the phenotypic ratio will always yield three of the dominant form and warn of the recessive form now let's just work a sort of a introductory kind
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of a simple problem before we end and let's use the example a human example to time a set of plans let's use the example of cystic fibrosis okay this is it inherited disorder and we're going to use the letter F okay so big ass is going to be the dominant allele and little ass is going to be the recessive okay and we have to understand how this disorder is inherited okay it is a
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it is a recessive disorder so what that means is the dominant allele is actually the normal or the healthy form of the gene the recessive allele is the affected allele so Gina typically because everybody gets to right we're a diploid organism so we get two copies of this particular genes so the possible genotypes are big-ass bigass big f little F Orlin left little F so big after that means they put the person it inherited to normal healthy genes so
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this person is normal right normal healthy no cystic fibrosis this individual inherited one normal and one effective okay they are healthy they do not have cystic fibrosis but we would say that they are a carrier so they don't have a disorder themselves but their carrier in other words they can still pass this effective allele on to their offspring now this genotype this is an effective individual meaning they have cystic fibrosis so let's say that
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that a problem says that there are two parents and they both have some family history of cystic fibrosis and so they have had genetic testing and they have determined that both the parents the female was okay and the male parent are both carriers so they're healthy but they're carriers so the first thing that we say is ok then we know that this one's genotype must be big a little less and the father's genotype must be against little s and the question is
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what percentage of their offspring would likely be affected with cystic fibrosis how many would have cystic fibrosis so we need to set up a punnett square again this is one trait right so we know that the box is going to have going to be a for Fox punnett square and we need to put the gametes of one parent across the top and one across the side so since the parents have the same genotype then it really does it doesn't matter we just need to make sure we keep track of both
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so we need to put half right for each gamete so the female parent has both the big s and the little left so the gametes have equal percentage chance of being of having the dominant or the recessive form that's for the eggs same thing with the sperm the male has a both a dominant and recessive form that can produce that can be produced in the gametes so we do this cross and we fill them in they will find out what the likelihood is that their offspring are going to have cystic
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fibrosis so first of all our genotypic ratio is one to two to one in other words this one is normal healthy no carrier this one is healthy but a carrier these two and this one is the effective genotype so the phenotypic ratio is three that do not have cystic fibrosis even though we have two carriers right to one individual that's affected but if they are looking at the likelihood they would have one child that is healthy non carrier two children
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that are healthy but they are carriers and this one child or one for percentage chance or twenty five percent chance that they would have a child with cystic fibrosis
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