Genetic Variation During Meiosis

by Jason Amores Sumpter
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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