In this video, we're going to talk about how meiosis leads to such incredible genetic diversity and variability. That's mainly due to 2 events, and those are crossing over and independent assortment. So crossing over is the process in which pairs of homologous chromosomes exchange genetic material. So, basically, the homologous chromosomes are going to be swapping DNA which will create non-sister chromatids, and this occurs during prophase 1 of meiosis 1. So it's one of the first events to occur in meiosis.
And when you're learning about this, you may hear the terms synapsis and chiasma. So synapsis refers to the alignment between homologous pairs of chromosomes. More specifically, it's those homologous chromosomes aligning their DNA sequence at similar alleles. So, if you look at our image here we have this pair of homologous chromosomes and each of these is comprised of identical sister chromatids. So this one and this one are identical, and this one and this one are identical.
And these homologous chromosomes are going to be similar in size, similar in shape, they're also going to have similar genes, but they can have different variations or different alleles of those genes. So I'm going to represent synapsis by just drawing a line in between them to show the alignment between those DNA sequences there. And that will kind of set the stage for crossing over to take place. Now next up we have our chiasma, which is the actual site of crossing over, and you can see the chiasma represented here where those chromosomes are literally crossing over and touching, making this kind of X shape, and the result of that is going to be what we see over here where now our blue chromosome has a little pink part and our pink chromosome has a little blue part. So they have exchanged that genetic material. And as you can see now we have non-sister chromatids.
So now this one and this one are no longer identical, as are this one and this one. And as you can imagine, that results in an enormous amount of possible genetic combinations. So, that is crossing over. Now next up we have independent assortment, and independent assortment is when pairs of homologous chromosomes are independently and randomly aligned, and this will happen during metaphase 1 of meiosis 1. And this can result in an enormous amount of possible genetic combinations.
So just to give you an idea of that, we have created a little graph here showing two possibilities of that random and independent alignment. And we have just used four chromosomes and, of course, humans would have 46. So this is a very simplistic version, but it gives you a good idea of how much diversity it can create. So here in this first row, we are looking at metaphase 1 of meiosis 1, and you can see in our first possibility here, our two maternal chromosomes have ended up on the left. Let me fix that right there really quick.
Alright. And our two paternal chromosomes have ended up on the right. And then in possibility number 2, we have one maternal chromosome here on the top left, a paternal one here on the top right, and then a paternal one here on the bottom left and a maternal one here on the bottom right. So, that is the result of that independent assortment.
Now in this middle row here, what we are looking at are the haploid daughter cells that would have resulted from meiosis 1. So you can see these are all completely different. So this has resulted in this cell over here is comprised completely of the maternal chromosomes. This one is comprised of the paternal chromosomes, and then these two over here are comprised of different versions of those maternal and paternal chromosomes. And then finally, looking at this bottom row here, we are looking at the haploid daughter cells that resulted from meiosis 2.
And so each of these represents a different combination. So we ended up with four different combinations in total. I will go ahead and number those: 1, 2, 3, and 4. Okay.
And again, of course, this is a very simplistic example using only four chromosomes and showing two possibilities of those combinations, and in real life, it would be much more complex. You can imagine how this in combination with that crossing over process is going to result in nearly infinite combinations of genetic variability. Alright. So that is genetic variation during meiosis and I will see you guys in the next one. Bye-bye.