Genetic Variation During Meiosis

in this video, we're going to talk about genetic variation during my oh, sis, And so recall from our previous lesson videos that my oh sis results in four Hat Lloyd cells that are all genetically different from one another. And so my Asus creates genetic variation. And so it turns out that my asses actually creates genetic diversity or genetic variation via two main events. And so, the first main event that creates genetic diversity during my oh sis is crossing over. And the second main event that creates genetic diversity during my oh sis is independent assortment. Now, in this video, we're going to focus mainly on the process of crossing over. But later, in our course, in a different video, we'll talk about the process of independent assortment. Now. Crossing over is the process in which pairs of homologous chromosomes actually exchange their genetic material, essentially swapping segments of DNA, and so you can see that during crossing over homologous chromosomes are going to cross over and swap or exchange their DNA. Now this process of crossing over is ultimately going to form non identical sister Crowe. Motives and crossing over occurs specifically during pro phase one of my Asus one. And so it's important to note that crossing over this process that creates genetic diversity Onley occurs during my Asus one, specifically pro phase one of my Asus one. But crossing over does not occur during my toe. Sis, which recall my toasts, creates genetically identical, not genetically diverse cells. Now, when your professors are explaining crossing over and when your textbooks describe crossing over there, likely going to mention these other terms called Synopsis and Key Osma. And so synapses is the process where homologous pairs of chromosomes actually align themselves and align their DNA sequences at similar a Leal's toe prompt crossing over. And so synapses is really just. This alignment of the DNA sequences between homologous chromosomes and key asthma is really just the sight of crossing over the attachment site between two homologous chromosomes, allowing these homologous chromosomes to cross over their genetic material. Exchange genetic material. But the key asthma is really just the sight of crossing over. And so, within this word, key asthma. You can see the root chi, which is actually a Greek letter that resembles an X, and so what you'll notice is that the key asthma really does resemble the formation of an X, and it represents the site of crossing over. And so, if we take a look at our image down below, notice that we're showing you one replicated chromosome over here that has two identical sister chroma tits. And we're showing you another replicated chromosome over here that also has two identical sister chromatic IDs and notice that these, uh replicated chromosomes are very, very similar in size and shape. They carry the same genes, but not necessarily the same versions of the genes or the same a Leal's. And so that makes these two chromosomes here homologous chromosomes. And again, you can see here that for this particular gene A. They have the same version of the gene, the capital a version of this gene but noticed that for Jean B, the blue chromosome has the capital B version of the gene, whereas the red chromosome has the lower case B version of the gene, and so homologous chromosomes are going to be similar in size, shape carry the same genes, but not necessarily the same versions of jeans. Now what's important to note is that again, uh, this sister Crowe omitted is exactly identical to this other sister committed and this is going to be the case before crossing over takes place. And the same goes for this sister chromatic here on this one and this one over here. They are identical to each other before crossing over takes place. And so again, the process of synapses is where the homologous pairs of chromosomes are going to align their DNA sequences at similar Leal's. And so you could see that synapses is shown here in the background here with the yellow background, where it's just showing the alignment here of the chromosomes to prompt crossing over to take place and then notice over here in the middle image that we have this overlapping region of the homologous chromosomes called the key asthma. And this represents again, the site of crossing over we're crossing over is going to take place. And so notice that at the very, very end of crossing over that we have a chromosome that is mostly blue but has a little bit of the pink chromosome, because there has been an exchange of the genetic material and then notice. Over here we have a chromosome that is mostly red, but has a little bit of blue again because there has been an exchange of the genetic material in the process of crossing over. And so this process of crossing over takes identical Sister Crowe motives and ends up converting them into non identical Sister Crowe motives. And so notice that this chromatic here is no longer identical to the chrome it'd that's over here because there has been this exchange of genetic material between these pairs of homologous chromosomes and so crossing over here, we're showing crossing over at one particular gene. But crossing over can actually occur between hundreds or thousands of genes between homologous chromosomes and crossing over occurs randomly with every single event of my oh sis. And so this is going to create an enormous amount of genetic diversity, swapping little bits and pieces of chromosomes between homologous pairs of chromosomes. And so again, crossing over is one of the main events that creates genetic diversity during my oh sis, and later in our course, we're going to talk about the second event that creates genetic diversity during my oh sis independent assortment. And so that concludes this video, and I'll see you all in our next one

So now that we've covered crossing over in our last lesson video the first main event that creates genetic diversity during my oh, sis, In this video, we're going to talk about the second main event that creates genetic diversity during my oh sis and that is independent assortment. And so independent assortment occurs specifically during meta phase one of my oh sis one. And of course, during meta phase, we know that the chromosomes air going to align themselves in the middle of the cell and specifically during meta Phase one of my Asus one, the chromosomes are going to align themselves in homologous pairs in two rows on the meta phase plate. And so independent assortment refers to the ability of these pairs of homologous chromosomes to independently and randomly align themselves on the meta phase plate during meta phase one of my Oasis one. And so when these pairs of homologous chromosomes independently and randomly align themselves during meta phase one, this results in an enormous amount of possible genetic combinations during my oh sis and again independent assortment along with crossing over is part of the reason why my oh sis results in four Hap Lloyd cells that are all genetically different from one another. And so independent assortment helps to create mawr possible genetic combinations, making it ah very, very difficult to get to cells that are genetically identical during the process of my oh sis. And so it's actually possible to calculate the number of combinations due to independent assortment by using the equation to raised to the power of n where n here is the exponents and n represents the Hap Lloyd number of chromosomes in a cell. And so we'll be able to get some practice applying this equation here to calculate the number of combinations due to independent assortment when we get to our image down below. And so if we take a look at our image down below, notice that we're showing you, uh, two possibilities Possibility number one and possibility number two for independent assortment as it occurs during my oh, Sis and Soe, notice that possibility Number one is over here generating combination one in combination too. And possibility number two is over here generating combination three and combination for. And so notice that this first row right here represents Meta phase one of my Asus one and of course, during metaphysics is we know that the chromosomes are going to align themselves in the middle of the cell. But during meta phase, one of my Asus one homologous chromosomes are going to pair up, and they're going to align themselves in two rows on the meta phase plate. And so notice here in our representation were using a total four chromosomes and these air replicated chromosome that you can see here. That one possibility for these chromosomes to align themselves is that all of the maternal chromosomes inherited from the mother line up on one side, and all of the paternal chromosomes inherited from the father line up on the other side. So that's one possibility if the's homologous chromosomes are independently and randomly aligning during meta phase one. But if they're independently and randomly aligning on the meta phase plate here, it's also possible for uh, not for all the the mother's chromosomes to not be on one side. And so notice here on this image that they're not lined up on one side, and the father's chromosomes are also not lined up on one side. So this is another possibility for how these chromosomes can independently and randomly align and so notice that each of these possibilities here is going to result in a different genetic combination. And so over here, in this possibility, notice that both of the mothers homologous chromosomes are going to go to the left to create this cell here that has two of the, uh, mother's chromosomes and one cell. And these two from the father would both separate to the right to create a cell that has both of the father's chromosomes. But if they aligned with this possibility here, notice that one of the mothers is going to go to the left and one of the fathers is going to go to the left. And so you end up getting a cell that has one of the mothers and one of the fathers chromosomes. And the same goes for this other cell. Over here, one of the mothers fathers goes to the right and one of the mothers goes to the right as well. And you get this combination right here. And so these combinations are different. All of these combinations are here are different. And what you see here in this row, uh, this road right here eyes representing Meta phase two of my oasis to And of course, during meta phase two of my closest to the chromosomes are aligning in one single file line like they do in mitosis as well. And so you can see here the alignment of the chromosomes in one single file line. And so this is going to result in different genetic combination. So notice here you have this combination Number one is one possibility on. Then you have combination number two over here is another possibility. And then over here, if independent assortment occurred in this way, you'll get combination. Three in combination four, which are different than combinations one and two. And all of these represent different genetic combinations. And they all resulted from independent assortment how these chromosomes can independently and randomly align themselves during meta phase one of my Asus one. And so ultimately, what we're saying here is that independent assortment, this event that occurs during meta Phase one here the random alignment of these homologous pairs of chromosome It's gonna create a lot of possible genetic combinations. And this is just showing four combinations here, uh, using just four total chromosomes. But we know that in human cells there are actually 46 chromosomes, and with 46 chromosomes that would create ah lot mawr possibilities. And so you can again calculate the number of possible combinations by using this formula here to raise to the power of n where the variable n again represents the Hap Lloyd number of chromosomes. And so notice here in this example that we're showing you we would say that to to the end, if we were using this equation. The end here, the Half Floyd number of chromosomes and our cells is two chromosomes. Because the end result of my oasis we know creates hap Lloyd cells and the half Floyd number here in this example is to So we would take two. And the end here would be to and so to raise to the 22 squared essentially is two times two, which is four. And so the number of possible genetic combinations when there are the Hap Lloyd number is two is four genetic possible combination. And that's what we're showing you here. The four genetic possible combinations. Uh, that result, if you would only have four, uh, you know, total chromosomes and the deploy itself and to total chromosomes and happily itself. And so this year concludes our brief introduction to independent assortment how it occurs during meta Phase one and really, how it just consists of homologous chromosomes independently and randomly aligning to create an enormous amount of possible genetic combinations during my oh sis. And we'll be able to get some practice applying these concepts as we move forward in our course, So I'll see you all in our next video.

All right. So here we have an example. Problem that says for a species with AHAP Lloyd number of chromosomes, which would be humans. Humans have a hap Lloyd number of 23 chromosomes. How many combinations of maternal and paternal chromosomes are possible for the game? It's based on the independent assortment of chromosomes during my ASUs, and we've got these four potential answer options down below. So really, what this problem is trying to ask us is how maney possible genetic combinations are there If the Hap Lloyd number of chromosomes is 23. And so what we need to recall from our last lesson video is that there is an equation to calculate the number of possible genetic combinations due to independent assortment. And so that equation is right here. The number of possible genetic combinations due to independent assortment is equal to two raised to the power of n where n is equal to the Hap Lloyd number of chromosomes. And so, for this equation, all we need to do is take two and raise it to the power of end again, the Hap Lloyd number of chromosomes. And we're told that the hap Lloyd number of chromosomes is 23 so to raise to the 23 when you type this into your calculator to raise to the power of 23 you'll get an answer of eight million, aN:aN:000NaN 388, possible genetic combinations. And this is a lot of possible genetic combinations when it comes to just independent assortment on its own. And this is every single time my ASUs occurs. And so the likelihood that these four gam it sells that result are going to have the same genetic combination is really unlikely if there are eight million, 388,608 possible genetic combinations. And so, of course, when we look at the answer options option, D says about eight million. And of course, that is going to be the closest one to the correct answer here. So Option D here is going to be the correct answer to this example, and that concludes this example. So I'll see you all in our next video

in this video, we're going to introduce non disjunction and so non disjunction is an error that can occur during either my Asus one or My Asus two. When chromosomes fail, two separate from each other, which can result in an you employed cells now and you employed cells. Our cells that are going to contain either too many or too few chromosomes and again and employed cells can be the result of a non disjunction. Now non destructions resulting in an employed cells can lead to genetic disorders for example, trisomy 21 or down syndrome or it could even lead to cell death. And so let's take a look at our image down below, which is showing you non disjunction during an A phase one of my oasis one or, uh, in phase two of my Asus two. And so notice here at the top, we're showing you a cell undergoing my oh sis one. And here at the bottom, we're showing you a cell undergoing my oasis to and again. Non disjunction can occur either during my hostess one or my oasis to when thes chromosomes are going to fail to separate properly. And so here what you can see is during meta phase one of my Asus one. The homologous chromosomes are going to, uh, randomly and, uh, independently align themselves in two rows on the meta phase plate. And so what you'll see here is in this image, we're showing you the non disjunction of a small blue chromosome. And so this small blue chromosome, if anna phase were to occur properly, it should shift over to this side of the cell. However, if a non disjunction occurs of the small blue chromosome, notice that the small blue chromosome is actually going to go to the same side as its homologous chromosome pair. And so this side over here is going to be missing the homologous chromosome, whereas this side over here is going to have an additional homologous chromosome. And so what you'll notice is that this cell here, which would represent the cell here at the top, is going to have to many chromosomes. And so if you have too many chromosomes, that is going to be a type of annual ploy, I'd so on DSO notice that this cell over here on Lee has one replicated chromosome, so it has too few chromosomes. And so you could see something similar occurring with my Asus two down below on again in my oasis to the chromosomes all line up in one single file wrote. And this time you could see that there's non disjunction of the large red sister chromatic IDs. And so, usually, during my Asus two, this sister Crowe matted would go, uh, to the bottom and the other sister chromatic, would go to the top. But if there is non disjunction, then notice that this bottom, the sister chromatic here, is not going to separate. It's going to fail to separate, and so notice that both sister Chromatic would end up over in the same cell and this cell would be lacking. Ah, sister chrome, it'd. And so again you would end up getting a cell that has too many chromosomes and a cell that has too few chromosomes. And so again, if a cell has either too many or too few chromosomes, they're referred to as an employed cells. And again, um, this non disjunction can lead to genetic disorders such as again Trisomy 21 or Down syndrome and trisomy 21 askew can see here try as a route that means three. And Trisomy 21 is referring to having three copies of chromosome 21. And so, if we take a look at this, carry a type that we have over here on the right, notice that there are two pairs of every single chromosome except for this pair right here. And this pair noticed that there are actually three copies of this chromosome chromosome 21 that leads to the genetic disorder trisomy 21 which is Down syndrome. And so we're showing you a baby here, a cute baby with down syndrome and so which you'll notice here is that we have finished our lesson here introducing non disjunction and how non disjunction is an error that can occur during my oasis, where chromosomes or sister chromatic has failed to separate, resulting in an applied cells with either too many or too few chromosomes. And so we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video