[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.05,0:00:03.66,Default,,0000,0000,0000,,We've gone over the general idea behind mitosis and meiosis.
Dialogue: 0,0:00:03.66,0:00:05.77,Default,,0000,0000,0000,,It's a good idea in this video to go a little bit more in detail.
Dialogue: 0,0:00:05.77,0:00:07.74,Default,,0000,0000,0000,,I've already done a video on mitosis,
Dialogue: 0,0:00:07.74,0:00:11.01,Default,,0000,0000,0000,,and in this one,we'll go into the details of meiosis.
Dialogue: 0,0:00:11.01,0:00:17.67,Default,,0000,0000,0000,,Just as a review,mitosis,you start with a diploid cell,
Dialogue: 0,0:00:17.67,0:00:20.02,Default,,0000,0000,0000,,and you end up with two diploid cells.
Dialogue: 0,0:00:20.02,0:00:23.53,Default,,0000,0000,0000,,Essentially, it just duplicates itself.And formally,
Dialogue: 0,0:00:23.53,0:00:26.76,Default,,0000,0000,0000,,mitosis is really the process of the duplication of the nucleus,
Dialogue: 0,0:00:26.76,0:00:29.03,Default,,0000,0000,0000,,but it normally ends up with two entire cells.
Dialogue: 0,0:00:29.03,0:00:33.58,Default,,0000,0000,0000,,Cytokinesis takes place.So this is mitosis.
Dialogue: 0,0:00:33.58,0:00:36.50,Default,,0000,0000,0000,,We have a video on it where we go into the phases of it:
Dialogue: 0,0:00:36.50,0:00:44.02,Default,,0000,0000,0000,,prophase,metaphase,anaphase and telophase.
Dialogue: 0,0:00:45.00,0:00:48.93,Default,,0000,0000,0000,,Mitosis occurs in pretty much all of our somatic cells
Dialogue: 0,0:00:48.93,0:00:54.70,Default,,0000,0000,0000,,as our skin cells replicate,and our hair cells
Dialogue: 0,0:00:54.70,0:00:58.90,Default,,0000,0000,0000,,and all the tissue in our body as it duplicates itself,
Dialogue: 0,0:00:58.90,0:01:00.01,Default,,0000,0000,0000,,it goes through mitosis.
Dialogue: 0,0:01:00.01,0:01:03.13,Default,,0000,0000,0000,,Meiosis occurs in the germ cells and it's used essentially to
Dialogue: 0,0:01:03.13,0:01:07.56,Default,,0000,0000,0000,,produce gametes to facilitate sexual reproduction.
Dialogue: 0,0:01:07.56,0:01:11.51,Default,,0000,0000,0000,,So if I start off with a diploid cell,
Dialogue: 0,0:01:11.51,0:01:15.05,Default,,0000,0000,0000,,and that's my diploid cell right there,this would be a germ cell.
Dialogue: 0,0:01:15.05,0:01:19.06,Default,,0000,0000,0000,,It's not just any cell in the body.It's a germ cell.
Dialogue: 0,0:01:19.06,0:01:22.82,Default,,0000,0000,0000,,It could undergo mitosis to produce more germ cells,
Dialogue: 0,0:01:22.82,0:01:24.67,Default,,0000,0000,0000,,but we'll talk about how it produces the gametes.
Dialogue: 0,0:01:24.67,0:01:28.04,Default,,0000,0000,0000,,It actually goes under two rounds.
Dialogue: 0,0:01:28.04,0:01:29.82,Default,,0000,0000,0000,,They're combined,called meiosis,
Dialogue: 0,0:01:29.82,0:01:35.36,Default,,0000,0000,0000,,but the first round you could call it meiosis 1,so I'll call that M1.
Dialogue: 0,0:01:35.36,0:01:37.48,Default,,0000,0000,0000,,I'm not talking about the money supply here.
Dialogue: 0,0:01:37.48,0:01:39.73,Default,,0000,0000,0000,,And in the first round of meiosis,
Dialogue: 0,0:01:39.73,0:01:45.02,Default,,0000,0000,0000,,this diploid cell essentially splits into two haploid cells.
Dialogue: 0,0:01:45.02,0:01:47.59,Default,,0000,0000,0000,,So if you started off with 43 chromosomes,
Dialogue: 0,0:01:47.59,0:01:50.83,Default,,0000,0000,0000,,you formally have 23 chromosomes in each one,
Dialogue: 0,0:01:50.83,0:01:53.39,Default,,0000,0000,0000,,or you can almost view it if you have 23 pairs here,
Dialogue: 0,0:01:53.39,0:01:59.09,Default,,0000,0000,0000,,each have two chromosomes,those pairs get split into this stage.
Dialogue: 0,0:01:59.09,0:02:04.20,Default,,0000,0000,0000,,And then in meiosis 2,
Dialogue: 0,0:02:04.21,0:02:11.00,Default,,0000,0000,0000,,these things get split in a mechanism very similar to mitosis.
Dialogue: 0,0:02:11.00,0:02:13.09,Default,,0000,0000,0000,,We'll see that when we actually go through the phases.
Dialogue: 0,0:02:13.09,0:02:16.01,Default,,0000,0000,0000,,In fact,the prophase,metaphase,anaphase,telophase
Dialogue: 0,0:02:16.01,0:02:19.87,Default,,0000,0000,0000,,also exist in each of these phases of meiosis.
Dialogue: 0,0:02:19.87,0:02:22.00,Default,,0000,0000,0000,,So let me just draw the end product.
Dialogue: 0,0:02:22.00,0:02:31.07,Default,,0000,0000,0000,,The end product is you have four cells and each of them are haploid.
Dialogue: 0,0:02:32.02,0:02:34.88,Default,,0000,0000,0000,,And you could already see,this process right here,
Dialogue: 0,0:02:34.88,0:02:38.40,Default,,0000,0000,0000,,you essentially split up your chromosomes,
Dialogue: 0,0:02:38.40,0:02:40.49,Default,,0000,0000,0000,,because you end up with half in each one,but here,
Dialogue: 0,0:02:40.49,0:02:43.99,Default,,0000,0000,0000,,you start with N and you end up with two chromosomes that each have N,
Dialogue: 0,0:02:43.99,0:02:46.03,Default,,0000,0000,0000,,so it's very similar to this.You preserve the number of chromosomes.
Dialogue: 0,0:02:46.03,0:02:49.03,Default,,0000,0000,0000,,So let's delve into the details of how it all happens.
Dialogue: 0,0:02:49.03,0:02:53.02,Default,,0000,0000,0000,,So all cells spend most of their time in interphase.
Dialogue: 0,0:02:53.02,0:02:56.32,Default,,0000,0000,0000,,Interphase is just a time when the cell is
Dialogue: 0,0:02:56.32,0:03:00.77,Default,,0000,0000,0000,,living and transcribing and doing what it needs to do.
Dialogue: 0,0:03:00.77,0:03:02.23,Default,,0000,0000,0000,,But just like in mitosis,
Dialogue: 0,0:03:02.23,0:03:06.92,Default,,0000,0000,0000,,one key thing does happen during the interphase, and actually,
Dialogue: 0,0:03:06.92,0:03:10.03,Default,,0000,0000,0000,,it happens during the same thing, the S phase of the interphase.
Dialogue: 0,0:03:10.03,0:03:15.03,Default,,0000,0000,0000,,So if that's my cell,that's my nucleus right here.
Dialogue: 0,0:03:15.03,0:03:18.25,Default,,0000,0000,0000,,And I'm going to draw it as chromosomes,but you have to remember that
Dialogue: 0,0:03:18.25,0:03:22.66,Default,,0000,0000,0000,,when we're outside of mitosis or meiosis formally,
Dialogue: 0,0:03:22.66,0:03:24.86,Default,,0000,0000,0000,,the chromosomes are all unwound,
Dialogue: 0,0:03:24.86,0:03:28.74,Default,,0000,0000,0000,,and they exist as chromatin,which we've talked about before.
Dialogue: 0,0:03:28.74,0:03:31.01,Default,,0000,0000,0000,,It's kind of the unwound state of the DNA.
Dialogue: 0,0:03:31.01,0:03:32.54,Default,,0000,0000,0000,,But I'm going to draw them wound up
Dialogue: 0,0:03:32.55,0:03:35.00,Default,,0000,0000,0000,,because I need to show you that they replicate.
Dialogue: 0,0:03:35.00,0:03:36.07,Default,,0000,0000,0000,,Now,I'm going to be a little careful here.
Dialogue: 0,0:03:36.07,0:03:40.02,Default,,0000,0000,0000,,In the mitosis video,I just had two chromosomes.
Dialogue: 0,0:03:40.02,0:03:42.03,Default,,0000,0000,0000,,They replicated and then they split apart.
Dialogue: 0,0:03:42.03,0:03:43.35,Default,,0000,0000,0000,,When we talk about meiosis,
Dialogue: 0,0:03:43.36,0:03:46.06,Default,,0000,0000,0000,,we have to be careful to show the homologous pairs.
Dialogue: 0,0:03:46.06,0:03:49.00,Default,,0000,0000,0000,,So let's say that I have two homologous pairs.
Dialogue: 0,0:03:49.00,0:03:54.00,Default,,0000,0000,0000,,So let's say I have--let me do it in appropriate colors.
Dialogue: 0,0:03:54.00,0:03:56.08,Default,,0000,0000,0000,,So this is the one I got from my dad.
Dialogue: 0,0:03:56.08,0:04:00.04,Default,,0000,0000,0000,,This is the one I got from my mom. They're homologous.
Dialogue: 0,0:04:00.04,0:04:05.33,Default,,0000,0000,0000,,And let's say that I have another one that I got from my dad.
Dialogue: 0,0:04:06.06,0:04:08.07,Default,,0000,0000,0000,,Let me do it in blue.
Dialogue: 0,0:04:08.07,0:04:11.09,Default,,0000,0000,0000,,Actually,maybe I should do all the ones from my dad in this color.
Dialogue: 0,0:04:11.09,0:04:14.06,Default,,0000,0000,0000,,Maybe it's a little bit longer. You get the idea.
Dialogue: 0,0:04:14.06,0:04:18.05,Default,,0000,0000,0000,,And then a homologous one for my mom that's also a little bit longer.
Dialogue: 0,0:04:18.05,0:04:20.91,Default,,0000,0000,0000,,Now,during the S phase of the interphase--
Dialogue: 0,0:04:20.91,0:04:23.56,Default,,0000,0000,0000,,and this is just like what happens in mitosis,
Dialogue: 0,0:04:23.56,0:04:27.54,Default,,0000,0000,0000,,so you can almost view it as it always happens during interphase.
Dialogue: 0,0:04:27.54,0:04:29.08,Default,,0000,0000,0000,,It doesn't happen in either meiosis or mitosis.
Dialogue: 0,0:04:29.08,0:04:32.06,Default,,0000,0000,0000,,You have replication of your DNA.
Dialogue: 0,0:04:32.06,0:04:34.94,Default,,0000,0000,0000,,So each of these from the homologous pair--and remember,
Dialogue: 0,0:04:34.94,0:04:38.22,Default,,0000,0000,0000,,homologous pairs mean that they're not identical chromosomes,
Dialogue: 0,0:04:38.22,0:04:41.00,Default,,0000,0000,0000,,but they do code for the same genes.
Dialogue: 0,0:04:41.00,0:04:43.67,Default,,0000,0000,0000,,They might have different versions or different alleles
Dialogue: 0,0:04:43.67,0:04:45.82,Default,,0000,0000,0000,,for a gene or for a certain trait,
Dialogue: 0,0:04:45.82,0:04:48.05,Default,,0000,0000,0000,,but they code essentially for the same kind of stuff.
Dialogue: 0,0:04:48.05,0:04:49.70,Default,,0000,0000,0000,,Now,replication of these,
Dialogue: 0,0:04:49.70,0:04:54.05,Default,,0000,0000,0000,,so each of these chromosomes in this pair replicate.
Dialogue: 0,0:04:54.05,0:04:58.85,Default,,0000,0000,0000,,So that one from my dad replicates like this,
Dialogue: 0,0:04:58.85,0:05:02.39,Default,,0000,0000,0000,,it replicates and it's connected by a centromere,
Dialogue: 0,0:05:02.39,0:05:05.98,Default,,0000,0000,0000,,and the one from my mom replicates like that,
Dialogue: 0,0:05:05.98,0:05:09.64,Default,,0000,0000,0000,,and it's connected by a centromere like that,
Dialogue: 0,0:05:09.65,0:05:11.00,Default,,0000,0000,0000,,and then the other one does as well.
Dialogue: 0,0:05:11.00,0:05:12.00,Default,,0000,0000,0000,,That's the shorter one.
Dialogue: 0,0:05:12.00,0:05:14.02,Default,,0000,0000,0000,,Oh,that's the longer one,actually.
Dialogue: 0,0:05:14.02,0:05:15.01,Default,,0000,0000,0000,,That's the longer one.
Dialogue: 0,0:05:15.01,0:05:16.60,Default,,0000,0000,0000,,I should be a little bit more explicit in
Dialogue: 0,0:05:16.60,0:05:18.01,Default,,0000,0000,0000,,which one's shorter and longer.
Dialogue: 0,0:05:18.01,0:05:20.29,Default,,0000,0000,0000,,The one from my mom does the same thing.
Dialogue: 0,0:05:20.29,0:05:21.87,Default,,0000,0000,0000,,This is in the S phase of interphase.
Dialogue: 0,0:05:21.87,0:05:25.08,Default,,0000,0000,0000,,We haven't entered the actual cell division yet.
Dialogue: 0,0:05:25.08,0:05:27.15,Default,,0000,0000,0000,,And the same thing is true--
Dialogue: 0,0:05:27.15,0:05:30.58,Default,,0000,0000,0000,,and this is kind of a little bit of a sideshow--of the centrosomes.
Dialogue: 0,0:05:30.58,0:05:33.23,Default,,0000,0000,0000,,And we saw in the mitosis video that these are involved in
Dialogue: 0,0:05:33.24,0:05:36.88,Default,,0000,0000,0000,,kind of eventually creating the microtubule structure
Dialogue: 0,0:05:36.88,0:05:38.40,Default,,0000,0000,0000,,in pulling everything apart,
Dialogue: 0,0:05:38.40,0:05:41.35,Default,,0000,0000,0000,,but you'll have one centrosome that's hanging out here,
Dialogue: 0,0:05:41.36,0:05:43.83,Default,,0000,0000,0000,,and then it facilitates its own replication,
Dialogue: 0,0:05:43.83,0:05:46.01,Default,,0000,0000,0000,,so then you have two centrosomes.
Dialogue: 0,0:05:46.01,0:05:49.97,Default,,0000,0000,0000,,So this is all occurring in the interphase,
Dialogue: 0,0:05:49.97,0:05:54.09,Default,,0000,0000,0000,,and particularly in the S part of the interphase,not the growth part.
Dialogue: 0,0:05:54.09,0:05:58.33,Default,,0000,0000,0000,,But once that's happens,we're ready--
Dialogue: 0,0:05:58.33,0:06:02.02,Default,,0000,0000,0000,,in fact,we're ready for either mitosis or meiosis,
Dialogue: 0,0:06:02.02,0:06:04.09,Default,,0000,0000,0000,,but we're going to do meiosis now.This is a germ cell.
Dialogue: 0,0:06:04.09,0:06:09.01,Default,,0000,0000,0000,,So what happens is we enter into prophase I.
Dialogue: 0,0:06:09.01,0:06:10.99,Default,,0000,0000,0000,,So if you remember,in my--let me write this down
Dialogue: 0,0:06:10.99,0:06:12.05,Default,,0000,0000,0000,,because I think it's important.
Dialogue: 0,0:06:12.05,0:06:26.07,Default,,0000,0000,0000,,In mitosis you have prophase,metaphase, anaphase and telophase.
Dialogue: 0,0:06:26.07,0:06:29.09,Default,,0000,0000,0000,,I won't keep writing phase down.PMAT.
Dialogue: 0,0:06:29.09,0:06:32.88,Default,,0000,0000,0000,,In meiosis,you experience these in each stage,
Dialogue: 0,0:06:32.88,0:06:37.51,Default,,0000,0000,0000,,so you have to prophase I,followed by metaphase I,
Dialogue: 0,0:06:37.51,0:06:41.00,Default,,0000,0000,0000,,followed by anaphase I,followed by telophase I.
Dialogue: 0,0:06:41.00,0:06:43.87,Default,,0000,0000,0000,,Then after you've done meiosis 1,then it all happens again.
Dialogue: 0,0:06:43.87,0:06:46.90,Default,,0000,0000,0000,,You have prophase II,followed by metaphase II,
Dialogue: 0,0:06:46.90,0:06:50.04,Default,,0000,0000,0000,,followed by anaphase II,followed by telophase.
Dialogue: 0,0:06:50.04,0:06:52.54,Default,,0000,0000,0000,,So if you really just want to memorize the names,
Dialogue: 0,0:06:52.54,0:06:54.88,Default,,0000,0000,0000,,which you unfortunately have to do in this,
Dialogue: 0,0:06:54.88,0:06:57.15,Default,,0000,0000,0000,,especially if you're going to get tested on it,
Dialogue: 0,0:06:57.15,0:06:59.79,Default,,0000,0000,0000,,although it's not that important to kind of understand the concept of
Dialogue: 0,0:06:59.79,0:07:01.54,Default,,0000,0000,0000,,what's happening, you just have to remember
Dialogue: 0,0:07:01.54,0:07:03.32,Default,,0000,0000,0000,,prophase,metaphase,anaphase,telophase,
Dialogue: 0,0:07:03.32,0:07:05.01,Default,,0000,0000,0000,,and it'll really cover everything.
Dialogue: 0,0:07:05.01,0:07:09.04,Default,,0000,0000,0000,,You just after memorize in meiosis,it's happening twice.
Dialogue: 0,0:07:09.04,0:07:10.91,Default,,0000,0000,0000,,And what's happening is a little bit different,
Dialogue: 0,0:07:10.91,0:07:12.79,Default,,0000,0000,0000,,and that's what I really want to focus on here.
Dialogue: 0,0:07:12.79,0:07:17.02,Default,,0000,0000,0000,,So let's enter prophase I of meiosis I.
Dialogue: 0,0:07:17.02,0:07:25.02,Default,,0000,0000,0000,,So let me call this prophase I.So what's going to happen?
Dialogue: 0,0:07:25.02,0:07:27.71,Default,,0000,0000,0000,,So just like in prophase and mitosis,
Dialogue: 0,0:07:27.71,0:07:29.98,Default,,0000,0000,0000,,a couple of things start happening.
Dialogue: 0,0:07:29.98,0:07:41.47,Default,,0000,0000,0000,,Your nuclear envelope starts disappearing.
Dialogue: 0,0:07:42.06,0:07:45.01,Default,,0000,0000,0000,,The centromeres--sorry,not centromeres.
Dialogue: 0,0:07:45.01,0:07:47.04,Default,,0000,0000,0000,,I'm getting confused now.The centrosomes.
Dialogue: 0,0:07:47.04,0:07:51.01,Default,,0000,0000,0000,,The centromeres are these things connecting these sister chromatids.
Dialogue: 0,0:07:51.01,0:07:56.46,Default,,0000,0000,0000,,The centrosomes start facilitating the development of the spindles,
Dialogue: 0,0:07:56.46,0:08:02.02,Default,,0000,0000,0000,,and they start pushing apart a little bit from the spindles.
Dialogue: 0,0:08:02.02,0:08:03.31,Default,,0000,0000,0000,,They start pushing apart
Dialogue: 0,0:08:03.31,0:08:06.06,Default,,0000,0000,0000,,and going to opposite sides of the chromosomes.
Dialogue: 0,0:08:06.06,0:08:09.02,Default,,0000,0000,0000,,And this is the really important thing in prophase I.
Dialogue: 0,0:08:09.02,0:08:10.66,Default,,0000,0000,0000,,And actually,I'll make this point.
Dialogue: 0,0:08:10.66,0:08:13.08,Default,,0000,0000,0000,,Remember,in interface,even though I drew it this way,
Dialogue: 0,0:08:13.08,0:08:16.52,Default,,0000,0000,0000,,they don't exist in this state,the actual chromosomes.
Dialogue: 0,0:08:16.52,0:08:18.00,Default,,0000,0000,0000,,They exist more in a chromatin state.
Dialogue: 0,0:08:18.00,0:08:23.03,Default,,0000,0000,0000,,So if I were to really draw it,it would look like this.
Dialogue: 0,0:08:23.03,0:08:27.92,Default,,0000,0000,0000,,The chromosomes,it would all be all over the place,and it actually
Dialogue: 0,0:08:27.92,0:08:30.09,Default,,0000,0000,0000,,would be very difficult to actually see it in a microscope.
Dialogue: 0,0:08:30.09,0:08:34.89,Default,,0000,0000,0000,,It would just be a big mess of proteins and of histones,
Dialogue: 0,0:08:34.89,0:08:37.56,Default,,0000,0000,0000,,which are proteins,and the actual DNA.
Dialogue: 0,0:08:37.56,0:08:40.01,Default,,0000,0000,0000,,And that's what's actually referred to as the chromatin.
Dialogue: 0,0:08:40.01,0:08:44.02,Default,,0000,0000,0000,,Now,in prophase,that starts to form into the chromosomes.
Dialogue: 0,0:08:44.02,0:08:46.71,Default,,0000,0000,0000,,It starts to have a little bit of structure,and this is
Dialogue: 0,0:08:46.71,0:08:50.04,Default,,0000,0000,0000,,completely analogous to what happens in prophase in mitosis.
Dialogue: 0,0:08:50.04,0:08:52.39,Default,,0000,0000,0000,,Now,the one interesting thing that happens
Dialogue: 0,0:08:52.39,0:08:55.51,Default,,0000,0000,0000,,is that the homologous pairs line up.And actually,
Dialogue: 0,0:08:55.51,0:08:59.03,Default,,0000,0000,0000,,I drew it like that over here and maybe I should just cut and paste it
Dialogue: 0,0:08:59.03,0:09:00.09,Default,,0000,0000,0000,,Let me just do that.
Dialogue: 0,0:09:00.09,0:09:07.52,Default,,0000,0000,0000,,If I just cut and paste that,
Dialogue: 0,0:09:07.53,0:09:12.52,Default,,0000,0000,0000,,although I said that the nucleus is disappearing,
Dialogue: 0,0:09:12.52,0:09:15.03,Default,,0000,0000,0000,,so let me get rid of the nucleus.I already said that.
Dialogue: 0,0:09:15.03,0:09:18.05,Default,,0000,0000,0000,,The nucleus is slowly disassembling.
Dialogue: 0,0:09:18.05,0:09:22.01,Default,,0000,0000,0000,,The proteins are coming apart during this prophase I.
Dialogue: 0,0:09:22.01,0:09:23.05,Default,,0000,0000,0000,,I won't draw the whole cell,
Dialogue: 0,0:09:23.05,0:09:26.54,Default,,0000,0000,0000,,because what's interesting here is happening at the nuclear,
Dialogue: 0,0:09:26.54,0:09:30.03,Default,,0000,0000,0000,,or what once was the nucleus level.
Dialogue: 0,0:09:30.03,0:09:34.00,Default,,0000,0000,0000,,So the interesting thing here that's different from mitosis
Dialogue: 0,0:09:34.00,0:09:37.01,Default,,0000,0000,0000,,is that the homologous pairs line up next to each other.
Dialogue: 0,0:09:37.01,0:09:40.77,Default,,0000,0000,0000,,Not only do they line up,but they can actually share--
Dialogue: 0,0:09:40.77,0:09:43.58,Default,,0000,0000,0000,,they can actually have genetic recombination.
Dialogue: 0,0:09:43.58,0:09:47.07,Default,,0000,0000,0000,,So you have these points where analogous--
Dialogue: 0,0:09:47.07,0:09:49.60,Default,,0000,0000,0000,,or I guess you could say homologous-- points
Dialogue: 0,0:09:49.60,0:09:54.02,Default,,0000,0000,0000,,on two of these chromosomes will cross over each other.
Dialogue: 0,0:09:54.02,0:09:55.56,Default,,0000,0000,0000,,So let me draw that in detail.
Dialogue: 0,0:09:55.56,0:09:59.06,Default,,0000,0000,0000,,So let me just focus on maybe these two right here.
Dialogue: 0,0:09:59.06,0:10:04.64,Default,,0000,0000,0000,,So I have one chromosome from my dad,
Dialogue: 0,0:10:04.64,0:10:06.69,Default,,0000,0000,0000,,and it's made up of two chromatids,
Dialogue: 0,0:10:06.69,0:10:08.26,Default,,0000,0000,0000,,so it's already replicated,
Dialogue: 0,0:10:08.26,0:10:09.43,Default,,0000,0000,0000,,but we only consider it one chromosome,
Dialogue: 0,0:10:09.43,0:10:16.00,Default,,0000,0000,0000,,and then I have one from my mom in green.
Dialogue: 0,0:10:16.00,0:10:18.09,Default,,0000,0000,0000,,I'm going to draw it like that.
Dialogue: 0,0:10:18.09,0:10:23.03,Default,,0000,0000,0000,,One from my mom in green,and it also has two chromatids.
Dialogue: 0,0:10:23.03,0:10:26.61,Default,,0000,0000,0000,,Sometimes this is called a tetrad
Dialogue: 0,0:10:26.61,0:10:28.77,Default,,0000,0000,0000,,because it has four chromatids in it,
Dialogue: 0,0:10:28.77,0:10:33.05,Default,,0000,0000,0000,,but it's in a pair of homologous chromosomes.
Dialogue: 0,0:10:33.05,0:10:34.67,Default,,0000,0000,0000,,These are the centromeres,of course.
Dialogue: 0,0:10:34.67,0:10:37.25,Default,,0000,0000,0000,,What happens is you have crossing over,
Dialogue: 0,0:10:37.25,0:10:42.67,Default,,0000,0000,0000,,and it's a surprisingly organized process.
Dialogue: 0,0:10:42.67,0:10:45.04,Default,,0000,0000,0000,,When I say organized,it crosses over at a homologous point.
Dialogue: 0,0:10:45.04,0:10:47.63,Default,,0000,0000,0000,,It crosses over at a point where,
Dialogue: 0,0:10:47.63,0:10:52.53,Default,,0000,0000,0000,,for the most part,you're exchanging similar genes.
Dialogue: 0,0:10:52.53,0:10:53.82,Default,,0000,0000,0000,,It's not like one is getting two versions of a gene
Dialogue: 0,0:10:53.82,0:10:56.05,Default,,0000,0000,0000,,and the other is getting two versions of another gene.
Dialogue: 0,0:10:56.05,0:10:57.62,Default,,0000,0000,0000,,You're changing in a way that
Dialogue: 0,0:10:57.62,0:11:01.31,Default,,0000,0000,0000,,both chromosomes are still coding for the different genes,
Dialogue: 0,0:11:01.31,0:11:03.53,Default,,0000,0000,0000,,but they're getting different versions of those genes
Dialogue: 0,0:11:03.53,0:11:07.02,Default,,0000,0000,0000,,or different alleles, which are just versions of those genes.
Dialogue: 0,0:11:07.02,0:11:08.89,Default,,0000,0000,0000,,So once this is done,
Dialogue: 0,0:11:08.89,0:11:12.97,Default,,0000,0000,0000,,the ones from my father are now not completely from my father,
Dialogue: 0,0:11:12.97,0:11:15.01,Default,,0000,0000,0000,,so it might look something like this.
Dialogue: 0,0:11:15.01,0:11:18.04,Default,,0000,0000,0000,,Let me see,it'll look like this.
Dialogue: 0,0:11:18.04,0:11:21.50,Default,,0000,0000,0000,,The one from my father now has this little bit from my mother,
Dialogue: 0,0:11:21.50,0:11:26.74,Default,,0000,0000,0000,,and the one from my--oh,no,my mother's chromosome is green--
Dialogue: 0,0:11:26.74,0:11:27.68,Default,,0000,0000,0000,,a little bit from my mother,
Dialogue: 0,0:11:27.68,0:11:33.03,Default,,0000,0000,0000,,and the one from my mother has a little bit from my father.
Dialogue: 0,0:11:33.03,0:11:35.84,Default,,0000,0000,0000,,And this is really amazing because it shows you that
Dialogue: 0,0:11:35.84,0:11:39.75,Default,,0000,0000,0000,,this is so favorable for creating variation in a population
Dialogue: 0,0:11:39.75,0:11:44.02,Default,,0000,0000,0000,,that it has really become a formal part of the meiosis process.
Dialogue: 0,0:11:44.02,0:11:46.95,Default,,0000,0000,0000,,It happens so frequently.This isn't just some random fluke,
Dialogue: 0,0:11:46.95,0:11:49.04,Default,,0000,0000,0000,,and it happens in a reasonably organized way.
Dialogue: 0,0:11:49.04,0:11:51.24,Default,,0000,0000,0000,,It actually happens at a point
Dialogue: 0,0:11:51.25,0:11:56.01,Default,,0000,0000,0000,,where it doesn't kind of create junk genes.
Dialogue: 0,0:11:56.01,0:11:59.99,Default,,0000,0000,0000,,Because you can imagine,this cut-off point,which is called a chiasma,
Dialogue: 0,0:11:59.99,0:12:02.65,Default,,0000,0000,0000,,it could have happened in the middle of some gene,
Dialogue: 0,0:12:02.65,0:12:04.85,Default,,0000,0000,0000,,and it could have created some random noise,
Dialogue: 0,0:12:04.85,0:12:07.27,Default,,0000,0000,0000,,and it could have broken down some protein development
Dialogue: 0,0:12:07.28,0:12:09.09,Default,,0000,0000,0000,,in the future or who knows what.But it doesn't happen that way.
Dialogue: 0,0:12:09.09,0:12:11.32,Default,,0000,0000,0000,,It happens in a reasonably organized way,
Dialogue: 0,0:12:11.32,0:12:15.07,Default,,0000,0000,0000,,which kind of speaks to the idea that it's part of the process.
Dialogue: 0,0:12:15.07,0:12:17.99,Default,,0000,0000,0000,,So in prophase I,you also have this happening.
Dialogue: 0,0:12:17.99,0:12:18.89,Default,,0000,0000,0000,,So once that happens
Dialogue: 0,0:12:18.89,0:12:23.54,Default,,0000,0000,0000,,you could have this guy's got a little bit of that chromatid
Dialogue: 0,0:12:23.54,0:12:28.03,Default,,0000,0000,0000,,and then this guy's got a little bit of that chromatid.
Dialogue: 0,0:12:28.03,0:12:30.47,Default,,0000,0000,0000,,So all of this stuff happens in prophase I.
Dialogue: 0,0:12:30.47,0:12:32.05,Default,,0000,0000,0000,,You have this crossing over.
Dialogue: 0,0:12:32.05,0:12:36.04,Default,,0000,0000,0000,,The nuclear envelope starts to disassemble,
Dialogue: 0,0:12:36.04,0:12:39.66,Default,,0000,0000,0000,,and then all of these guys align and the chromatin starts
Dialogue: 0,0:12:39.66,0:12:42.69,Default,,0000,0000,0000,,forming into these more tightly wound structures of chromosomes.
Dialogue: 0,0:12:42.69,0:12:45.68,Default,,0000,0000,0000,,And really,that's all--when we talk about even mitosis,
Dialogue: 0,0:12:45.68,0:12:48.00,Default,,0000,0000,0000,,that's where a lot of the action really took place.
Dialogue: 0,0:12:48.00,0:12:51.84,Default,,0000,0000,0000,,Once that happens,then we're ready to enter into the metaphase I,
Dialogue: 0,0:12:51.84,0:12:54.09,Default,,0000,0000,0000,,so let's go down to metaphase I.
Dialogue: 0,0:12:54.09,0:13:01.92,Default,,0000,0000,0000,,In metaphase I--let me just copy and paste what I've already done--
Dialogue: 0,0:13:01.92,0:13:08.37,Default,,0000,0000,0000,,the nuclear envelope is now gone.
Dialogue: 0,0:13:09.07,0:13:17.01,Default,,0000,0000,0000,,The centrosomes have gone to opposite sides of the cell itself.
Dialogue: 0,0:13:17.01,0:13:22.00,Default,,0000,0000,0000,,Maybe I should draw the entire cell now that there's no nucleus.
Dialogue: 0,0:13:22.00,0:13:26.09,Default,,0000,0000,0000,,Let me erase the nucleus a little bit better than I've done.
Dialogue: 0,0:13:26.09,0:13:30.00,Default,,0000,0000,0000,,Let me erase all of that.
Dialogue: 0,0:13:30.00,0:13:34.04,Default,,0000,0000,0000,,And,of course,we have the spindles fibers that have been
Dialogue: 0,0:13:34.04,0:13:39.07,Default,,0000,0000,0000,,generated by now with the help of the centrosomes.
Dialogue: 0,0:13:39.07,0:13:40.90,Default,,0000,0000,0000,,And some of them,as we learned,
Dialogue: 0,0:13:40.90,0:13:44.53,Default,,0000,0000,0000,,this is exactly what happened in mitosis.
Dialogue: 0,0:13:44.53,0:13:45.58,Default,,0000,0000,0000,,They attach to the kinetochores,
Dialogue: 0,0:13:45.59,0:13:52.55,Default,,0000,0000,0000,,which are attached to the centromeres of these chromosomes.
Dialogue: 0,0:13:52.55,0:13:55.58,Default,,0000,0000,0000,,Now,what's interesting here is that they each attach--
Dialogue: 0,0:13:55.58,0:13:57.40,Default,,0000,0000,0000,,so this guy's going to attach to--
Dialogue: 0,0:13:57.41,0:14:00.09,Default,,0000,0000,0000,,and actually,let me do something interesting here.
Dialogue: 0,0:14:00.09,0:14:03.07,Default,,0000,0000,0000,,Instead of doing it this way,because I want to show that
Dialogue: 0,0:14:03.07,0:14:04.88,Default,,0000,0000,0000,,all my dad's chromosomes don't go to one side
Dialogue: 0,0:14:04.88,0:14:06.57,Default,,0000,0000,0000,,and all my mom's chromosomes don't go to the other side.
Dialogue: 0,0:14:06.57,0:14:09.31,Default,,0000,0000,0000,,So instead of drawing these two guys like this,
Dialogue: 0,0:14:09.31,0:14:12.58,Default,,0000,0000,0000,,let me see if I can flip them.Let me see.
Dialogue: 0,0:14:12.58,0:14:15.01,Default,,0000,0000,0000,,Let me just flip them the other way.
Dialogue: 0,0:14:15.01,0:14:18.32,Default,,0000,0000,0000,,Whether or not which direction they're flipped is completely random,
Dialogue: 0,0:14:18.32,0:14:20.05,Default,,0000,0000,0000,,and that's what adds to the variation.
Dialogue: 0,0:14:20.05,0:14:22.86,Default,,0000,0000,0000,,As we said before,sexual reproduction is key
Dialogue: 0,0:14:22.86,0:14:26.06,Default,,0000,0000,0000,,to introducing variation into a population.
Dialogue: 0,0:14:26.06,0:14:28.97,Default,,0000,0000,0000,,So that's the mom's and that's the dad's.They don't have to.
Dialogue: 0,0:14:28.97,0:14:31.32,Default,,0000,0000,0000,,All of the ones from my dad might have ended up on one side
Dialogue: 0,0:14:31.32,0:14:33.02,Default,,0000,0000,0000,,and all of them from my mom might end up on one side,
Dialogue: 0,0:14:33.02,0:14:34.92,Default,,0000,0000,0000,,although when you're talking about 23 pairs,
Dialogue: 0,0:14:34.92,0:14:38.07,Default,,0000,0000,0000,,the probability becomes a lot,lot lower.
Dialogue: 0,0:14:38.07,0:14:44.59,Default,,0000,0000,0000,,So this is one from my dad.Of course,it has some centromeres.
Dialogue: 0,0:14:44.59,0:14:46.07,Default,,0000,0000,0000,,Let me draw that there.
Dialogue: 0,0:14:46.07,0:14:50.90,Default,,0000,0000,0000,,And so these microspindles,some of them attach to kinetochores,
Dialogue: 0,0:14:50.90,0:14:54.05,Default,,0000,0000,0000,,which are these protein structures on the centromeres.
Dialogue: 0,0:14:54.05,0:14:57.01,Default,,0000,0000,0000,,And this is just like metaphase.
Dialogue: 0,0:14:57.01,0:15:00.00,Default,,0000,0000,0000,,It's very similar to metaphase in mitosis.
Dialogue: 0,0:15:00.00,0:15:05.01,Default,,0000,0000,0000,,This is called metaphase I,and everything aligns.
Dialogue: 0,0:15:05.01,0:15:08.04,Default,,0000,0000,0000,,Now we're going to enter anaphase I.
Dialogue: 0,0:15:08.04,0:15:12.50,Default,,0000,0000,0000,,Now,anaphase I is interesting,because remember,
Dialogue: 0,0:15:12.50,0:15:16.01,Default,,0000,0000,0000,,in mitosis in anaphase,the actual chromatids,
Dialogue: 0,0:15:16.01,0:15:18.08,Default,,0000,0000,0000,,the sister chromatids separated from each other.
Dialogue: 0,0:15:18.08,0:15:22.79,Default,,0000,0000,0000,,That's not the case in anaphase I here in meiosis.
Dialogue: 0,0:15:22.79,0:15:25.75,Default,,0000,0000,0000,,So when we enter anaphase I,
Dialogue: 0,0:15:25.75,0:15:28.65,Default,,0000,0000,0000,,you have just the homologous pairs separate,
Dialogue: 0,0:15:28.65,0:15:32.06,Default,,0000,0000,0000,,so the chromatids stay with their sister chromatids.
Dialogue: 0,0:15:32.06,0:15:37.01,Default,,0000,0000,0000,,So on this side,you'll have these to go there.
Dialogue: 0,0:15:37.01,0:15:45.00,Default,,0000,0000,0000,,While I have the green out,let me see if I can draw this respectably.
Dialogue: 0,0:15:45.00,0:15:49.07,Default,,0000,0000,0000,,I have the purple.It's a little bit shorter version here.
Dialogue: 0,0:15:49.07,0:15:53.04,Default,,0000,0000,0000,,He's got a little bit of a stub of green there.
Dialogue: 0,0:15:53.04,0:15:56.01,Default,,0000,0000,0000,,This guy's got little stub of purple there.
Dialogue: 0,0:15:56.01,0:16:00.00,Default,,0000,0000,0000,,And then they have this longer purple chromosome here.
Dialogue: 0,0:16:00.00,0:16:01.55,Default,,0000,0000,0000,,This is anaphase I.
Dialogue: 0,0:16:01.55,0:16:03.92,Default,,0000,0000,0000,,They're being pulled apart,but they're being pulled apart--
Dialogue: 0,0:16:03.92,0:16:06.82,Default,,0000,0000,0000,,the homologous pair is being pulled apart,
Dialogue: 0,0:16:06.82,0:16:10.06,Default,,0000,0000,0000,,not the actual chromosomes,not the chromatids.
Dialogue: 0,0:16:10.06,0:16:13.02,Default,,0000,0000,0000,,So let me just draw this.
Dialogue: 0,0:16:13.02,0:16:14.58,Default,,0000,0000,0000,,So then you have your microtubules.
Dialogue: 0,0:16:14.58,0:16:17.03,Default,,0000,0000,0000,,Some are connected to these kinetochores.You have your centromeres.
Dialogue: 0,0:16:19.07,0:16:21.45,Default,,0000,0000,0000,,Of course,all of this is occurring within the cell
Dialogue: 0,0:16:21.45,0:16:23.05,Default,,0000,0000,0000,,and these are getting pulled apart.
Dialogue: 0,0:16:23.05,0:16:27.36,Default,,0000,0000,0000,,So it's analogous to anaphase in mitosis,
Dialogue: 0,0:16:27.36,0:16:31.58,Default,,0000,0000,0000,,but the key difference is you're pulling apart homologous pairs.
Dialogue: 0,0:16:31.58,0:16:33.48,Default,,0000,0000,0000,,You're not actually splitting the chromosomes
Dialogue: 0,0:16:33.48,0:16:37.52,Default,,0000,0000,0000,,into their constituent chromatids,and that's key.
Dialogue: 0,0:16:37.52,0:16:40.72,Default,,0000,0000,0000,,And if you forget that,you can review the mitosis video.
Dialogue: 0,0:16:40.72,0:16:47.08,Default,,0000,0000,0000,,So this is anaphase I.
Dialogue: 0,0:16:48.03,0:16:51.00,Default,,0000,0000,0000,,And then as you could imagine,telophase I is essentially
Dialogue: 0,0:16:51.00,0:16:58.49,Default,,0000,0000,0000,,once these guys are at their respective ends of the cell--
Dialogue: 0,0:16:58.49,0:17:00.40,Default,,0000,0000,0000,,it's getting tiring redrawing all of these,
Dialogue: 0,0:17:00.40,0:17:05.00,Default,,0000,0000,0000,,but I guess it gives you time to let it all sink in.
Dialogue: 0,0:17:05.00,0:17:08.41,Default,,0000,0000,0000,,So these guys are now at the left end of the cell
Dialogue: 0,0:17:08.41,0:17:15.04,Default,,0000,0000,0000,,and these guys are now at the right end of the cell.
Dialogue: 0,0:17:15.04,0:17:18.00,Default,,0000,0000,0000,,Now,the microtubules start to disassemble.
Dialogue: 0,0:17:18.00,0:17:21.87,Default,,0000,0000,0000,,So maybe they're there a little bit,but they're disassembling.
Dialogue: 0,0:17:21.87,0:17:25.03,Default,,0000,0000,0000,,You still have your centromeres here and they're at opposite poles.
Dialogue: 0,0:17:25.03,0:17:27.53,Default,,0000,0000,0000,,And to some degree,in the early part of telophase,
Dialogue: 0,0:17:27.53,0:17:28.84,Default,,0000,0000,0000,,they're still pushing the cell apart,
Dialogue: 0,0:17:28.84,0:17:32.05,Default,,0000,0000,0000,,and at the same time,you have cytokinesis happening.
Dialogue: 0,0:17:32.05,0:17:35.02,Default,,0000,0000,0000,,So by the end of telophase I,
Dialogue: 0,0:17:35.02,0:17:41.62,Default,,0000,0000,0000,,you have the actual cytoplasm splitting during telophase right there,
Dialogue: 0,0:17:41.62,0:17:44.08,Default,,0000,0000,0000,,and the nuclear envelope is forming.
Dialogue: 0,0:17:44.08,0:17:50.00,Default,,0000,0000,0000,,You can almost view it as the opposite of prophase.
Dialogue: 0,0:17:50.00,0:17:52.85,Default,,0000,0000,0000,,The nuclear envelope is forming,and by the end of telophase I,
Dialogue: 0,0:17:52.85,0:17:58.00,Default,,0000,0000,0000,,it will have completely divided.So this is telophase I.
Dialogue: 0,0:17:58.00,0:18:02.07,Default,,0000,0000,0000,,Now,notice:we started off with a diploid cell,right?
Dialogue: 0,0:18:02.07,0:18:09.03,Default,,0000,0000,0000,,It had two pairs of homologous chromosome,but it had four chromosomes.
Dialogue: 0,0:18:09.03,0:18:13.03,Default,,0000,0000,0000,,Now,each cell only has two chromosomes.
Dialogue: 0,0:18:13.03,0:18:17.98,Default,,0000,0000,0000,,Essentially,each cell got one of the pair of each
Dialogue: 0,0:18:17.98,0:18:20.30,Default,,0000,0000,0000,,of those homologous pairs,but it was done randomly,
Dialogue: 0,0:18:20.30,0:18:23.06,Default,,0000,0000,0000,,and that's where a lot of the variation is introduced.
Dialogue: 0,0:18:23.06,0:18:24.74,Default,,0000,0000,0000,,Now,once we're at this stage,
Dialogue: 0,0:18:24.74,0:18:28.63,Default,,0000,0000,0000,,each of these cells now undergo meiosis II,
Dialogue: 0,0:18:28.63,0:18:32.91,Default,,0000,0000,0000,,which is actually very similar to mitosis.And sometimes,
Dialogue: 0,0:18:32.91,0:18:35.64,Default,,0000,0000,0000,,there's actually an in-between stage called interphase II,
Dialogue: 0,0:18:35.64,0:18:37.83,Default,,0000,0000,0000,,where the cell kind of rests and whatever else,
Dialogue: 0,0:18:37.83,0:18:41.45,Default,,0000,0000,0000,,and actually the centromeres now have to duplicate again.
Dialogue: 0,0:18:41.45,0:18:43.77,Default,,0000,0000,0000,,So these two cells--I've drawn them separately--
Dialogue: 0,0:18:43.77,0:18:46.00,Default,,0000,0000,0000,,let's see what happens next.
Dialogue: 0,0:18:46.00,0:18:49.11,Default,,0000,0000,0000,,So let's say that the centromere--actually,I shouldn't have drawn
Dialogue: 0,0:18:49.11,0:18:50.67,Default,,0000,0000,0000,,the centromere inside the nucleus like that.
Dialogue: 0,0:18:50.67,0:18:54.41,Default,,0000,0000,0000,,The centromere's going to be outside the nucleus,
Dialogue: 0,0:18:54.41,0:19:00.08,Default,,0000,0000,0000,,outside of the newly formed nucleus there and there.
Dialogue: 0,0:19:00.08,0:19:06.04,Default,,0000,0000,0000,,And then it'll actually replicate itself at this point as well.
Dialogue: 0,0:19:06.04,0:19:10.04,Default,,0000,0000,0000,,So now we have two cells.
Dialogue: 0,0:19:10.04,0:19:16.60,Default,,0000,0000,0000,,Let me just cut and paste what I have.I have this one,
Dialogue: 0,0:19:16.60,0:19:20.03,Default,,0000,0000,0000,,this chromosome right here.
Dialogue: 0,0:19:20.03,0:19:22.19,Default,,0000,0000,0000,,It's got this little green stub there
Dialogue: 0,0:19:22.19,0:19:25.56,Default,,0000,0000,0000,,and then I have this longer fully green chromosome there.
Dialogue: 0,0:19:25.56,0:19:32.03,Default,,0000,0000,0000,,Now,this guy,he's got this little purple stub here.
Dialogue: 0,0:19:32.03,0:19:35.07,Default,,0000,0000,0000,,Let me draw this whole purple chromosome there.
Dialogue: 0,0:19:35.07,0:19:41.03,Default,,0000,0000,0000,,Then this guy has one chromatid like that and one chromatid like that.
Dialogue: 0,0:19:41.03,0:19:46.30,Default,,0000,0000,0000,,Now,when we enter prophase II,
Dialogue: 0,0:19:46.30,0:19:50.18,Default,,0000,0000,0000,,what do you think is going to happen?Well,just like before,
Dialogue: 0,0:19:50.18,0:19:56.00,Default,,0000,0000,0000,,you have your nuclear envelope that formed in telophase I.
Dialogue: 0,0:19:56.00,0:20:06.03,Default,,0000,0000,0000,,It's kind of a temporary thing.It starts to disintegrate again.
Dialogue: 0,0:20:06.03,0:20:10.05,Default,,0000,0000,0000,,And then you have your centromeres.
Dialogue: 0,0:20:10.05,0:20:13.55,Default,,0000,0000,0000,,They start pushing apart so now I had two centromeres.
Dialogue: 0,0:20:13.55,0:20:16.35,Default,,0000,0000,0000,,They replicated,and now they start pushing apart
Dialogue: 0,0:20:16.35,0:20:19.02,Default,,0000,0000,0000,,while they generate their little spindles.
Dialogue: 0,0:20:19.02,0:20:20.78,Default,,0000,0000,0000,,They push apart in opposite directions.
Dialogue: 0,0:20:20.78,0:20:23.05,Default,,0000,0000,0000,,Now,this is happening in two cells,of course.
Dialogue: 0,0:20:23.05,0:20:24.69,Default,,0000,0000,0000,,They go in opposite directions
Dialogue: 0,0:20:24.70,0:20:27.00,Default,,0000,0000,0000,,while they generate their spindle fibers.
Dialogue: 0,0:20:27.00,0:20:28.22,Default,,0000,0000,0000,,And let me make it very clear that
Dialogue: 0,0:20:28.22,0:20:30.06,Default,,0000,0000,0000,,this is two cells we're talking about.
Dialogue: 0,0:20:30.06,0:20:35.01,Default,,0000,0000,0000,,That's one of them and that's the second of them.
Dialogue: 0,0:20:35.01,0:20:42.82,Default,,0000,0000,0000,,Now it's going to enter metaphase II,
Dialogue: 0,0:20:42.82,0:20:45.21,Default,,0000,0000,0000,,which is analogous to metaphase I,or metaphase in mitosis,
Dialogue: 0,0:20:45.21,0:20:48.00,Default,,0000,0000,0000,,where the chromosomes get lined up.
Dialogue: 0,0:20:48.00,0:20:49.00,Default,,0000,0000,0000,,Let me draw it this way.
Dialogue: 0,0:20:49.00,0:20:54.08,Default,,0000,0000,0000,,So now the centromeres,they've migrated to the two poles of the cell.
Dialogue: 0,0:20:54.08,0:20:57.87,Default,,0000,0000,0000,,So those are my centromeres.
Dialogue: 0,0:20:57.87,0:21:05.02,Default,,0000,0000,0000,,I have all of my spindles fibers.
Dialogue: 0,0:21:05.02,0:21:10.01,Default,,0000,0000,0000,,Oh,sorry,did I call those centromeres? The centrosomes.
Dialogue: 0,0:21:10.01,0:21:12.06,Default,,0000,0000,0000,,I don't know how long I've been calling them centromeres.
Dialogue: 0,0:21:12.06,0:21:14.08,Default,,0000,0000,0000,,These are centrosomes,and my brain keeps confusing them.
Dialogue: 0,0:21:14.08,0:21:16.34,Default,,0000,0000,0000,,The centromeres,and maybe this'll help you
Dialogue: 0,0:21:16.35,0:21:19.59,Default,,0000,0000,0000,,not do what I just did,the centromeres are the things
Dialogue: 0,0:21:19.59,0:21:22.00,Default,,0000,0000,0000,,that are connecting the two sister chromatids.
Dialogue: 0,0:21:22.00,0:21:23.00,Default,,0000,0000,0000,,Those are centromeres.
Dialogue: 0,0:21:23.00,0:21:26.58,Default,,0000,0000,0000,,Centrosomes are the things that are pushing back the--
Dialogue: 0,0:21:26.58,0:21:29.04,Default,,0000,0000,0000,,that generate the spindle fibers.
Dialogue: 0,0:21:29.04,0:21:31.55,Default,,0000,0000,0000,,The chromosomes line up during metaphase.
Dialogue: 0,0:21:31.55,0:21:33.91,Default,,0000,0000,0000,,Metaphase always involves the lining up of chromosomes
Dialogue: 0,0:21:33.91,0:21:38.07,Default,,0000,0000,0000,,so that one--let me just draw it.So I have that and that.
Dialogue: 0,0:21:38.07,0:21:41.68,Default,,0000,0000,0000,,This one's got a purple guy,too.
Dialogue: 0,0:21:41.68,0:21:43.64,Default,,0000,0000,0000,,This guy's got a purple guy,a long purple guy,
Dialogue: 0,0:21:43.64,0:21:46.88,Default,,0000,0000,0000,,and then there's a little stub for the other guy.
Dialogue: 0,0:21:46.88,0:21:52.71,Default,,0000,0000,0000,,This guy's got a long green guy and this guy's got a little green stub
Dialogue: 0,0:21:52.71,0:21:57.02,Default,,0000,0000,0000,,and then this is the short green guy right there.
Dialogue: 0,0:21:57.02,0:21:58.96,Default,,0000,0000,0000,,And,of course,they're being aligned.
Dialogue: 0,0:21:58.96,0:22:00.89,Default,,0000,0000,0000,,Some of these spindle fibers have been attached
Dialogue: 0,0:22:00.89,0:22:04.41,Default,,0000,0000,0000,,to the centromeres or the kinetochores that are on the centromeres
Dialogue: 0,0:22:04.41,0:22:09.06,Default,,0000,0000,0000,,that connect these two chromatids,these sister chromatids.
Dialogue: 0,0:22:09.06,0:22:11.58,Default,,0000,0000,0000,,And,of course,we don't have a nuclear membrane anymore,
Dialogue: 0,0:22:11.58,0:22:14.08,Default,,0000,0000,0000,,and these are,of course,two separate cells.
Dialogue: 0,0:22:14.08,0:22:17.67,Default,,0000,0000,0000,,And then you can guess what happens in anaphase II.
Dialogue: 0,0:22:17.67,0:22:24.02,Default,,0000,0000,0000,,It's just like anaphase in mitosis.
Dialogue: 0,0:22:24.02,0:22:28.40,Default,,0000,0000,0000,,These things get pulled apart by the kinetochore microtubules,
Dialogue: 0,0:22:28.40,0:22:29.81,Default,,0000,0000,0000,,while the other microtubules keep growing
Dialogue: 0,0:22:29.81,0:22:33.01,Default,,0000,0000,0000,,and push and these two things further apart.
Dialogue: 0,0:22:33.01,0:22:35.39,Default,,0000,0000,0000,,So let me show that.And they the key here:
Dialogue: 0,0:22:35.39,0:22:37.79,Default,,0000,0000,0000,,this is the difference between anaphase II and anaphase I.
Dialogue: 0,0:22:37.79,0:22:42.44,Default,,0000,0000,0000,,Anaphase I,the homologous pairs were broken up,
Dialogue: 0,0:22:42.44,0:22:45.02,Default,,0000,0000,0000,,but the chromosomes themselves were not.
Dialogue: 0,0:22:45.02,0:22:48.01,Default,,0000,0000,0000,,Now,in anaphase II,we don't have homologous pairs.
Dialogue: 0,0:22:48.01,0:22:51.02,Default,,0000,0000,0000,,We just have chromatid pairs,sister chromatids.
Dialogue: 0,0:22:51.02,0:22:57.00,Default,,0000,0000,0000,,Now,those are separated,which is very similar to anaphase in mitosis.
Dialogue: 0,0:22:57.00,0:22:59.48,Default,,0000,0000,0000,,So now,this guy gets pulled in that direction
Dialogue: 0,0:22:59.48,0:23:01.09,Default,,0000,0000,0000,,so it look something like this.
Dialogue: 0,0:23:01.09,0:23:04.08,Default,,0000,0000,0000,,The drawing here is the hardest part of this video.
Dialogue: 0,0:23:04.08,0:23:06.02,Default,,0000,0000,0000,,So that guy gets pulled there.
Dialogue: 0,0:23:06.02,0:23:08.05,Default,,0000,0000,0000,,That guy's getting pulled in that direction.
Dialogue: 0,0:23:08.05,0:23:10.08,Default,,0000,0000,0000,,He's got that little green stub on him.
Dialogue: 0,0:23:10.08,0:23:11.83,Default,,0000,0000,0000,,And then you have one green guy
Dialogue: 0,0:23:11.84,0:23:16.02,Default,,0000,0000,0000,,getting pulled in that direction with the longer chromosome.
Dialogue: 0,0:23:16.02,0:23:18.93,Default,,0000,0000,0000,,And then one of the other longer is getting pulled in that direction,
Dialogue: 0,0:23:18.94,0:23:21.01,Default,,0000,0000,0000,,and it's all by these microtubules
Dialogue: 0,0:23:21.01,0:23:23.74,Default,,0000,0000,0000,,connected at the kinetochore structures
Dialogue: 0,0:23:23.74,0:23:28.58,Default,,0000,0000,0000,,by a centrosome as kind of the coordinating body.
Dialogue: 0,0:23:28.58,0:23:30.03,Default,,0000,0000,0000,,It's all being pulled apart.
Dialogue: 0,0:23:30.03,0:23:32.96,Default,,0000,0000,0000,,Anaphase has always involved the pulling apart of
Dialogue: 0,0:23:32.96,0:23:36.04,Default,,0000,0000,0000,,the chromosomes or pulling apart of something.
Dialogue: 0,0:23:36.04,0:23:37.02,Default,,0000,0000,0000,,Let me put it that way.
Dialogue: 0,0:23:37.02,0:23:41.01,Default,,0000,0000,0000,,And it's happening on this side of the cell as well.
Dialogue: 0,0:23:41.01,0:23:43.58,Default,,0000,0000,0000,,Of course, this is all one cell.
Dialogue: 0,0:23:43.58,0:23:46.69,Default,,0000,0000,0000,,And just like in mitosis,
Dialogue: 0,0:23:46.69,0:23:49.87,Default,,0000,0000,0000,,as soon as the sister chromatids are split apart,
Dialogue: 0,0:23:49.87,0:23:53.09,Default,,0000,0000,0000,,they are now referred to as chromosomes,or sister chromosomes.
Dialogue: 0,0:23:53.09,0:23:55.05,Default,,0000,0000,0000,,And,of course,this is happening twice.
Dialogue: 0,0:23:55.05,0:23:59.56,Default,,0000,0000,0000,,This is also happening in the other cell.
Dialogue: 0,0:23:59.56,0:24:01.00,Default,,0000,0000,0000,,The other cell's a little bit cleaner.
Dialogue: 0,0:24:01.00,0:24:03.07,Default,,0000,0000,0000,,It didn't have that crossover occur.
Dialogue: 0,0:24:03.07,0:24:08.09,Default,,0000,0000,0000,,So you have the longer purple one.
Dialogue: 0,0:24:08.09,0:24:10.99,Default,,0000,0000,0000,,He gets split up into two chromatids,
Dialogue: 0,0:24:10.99,0:24:14.08,Default,,0000,0000,0000,,which we are now calling chromosomes,or sister chromosomes.
Dialogue: 0,0:24:14.08,0:24:19.99,Default,,0000,0000,0000,,And then this guy up here,he gets split up into this short green,
Dialogue: 0,0:24:19.99,0:24:23.34,Default,,0000,0000,0000,,and then there's a--let me do it this way--this short green,
Dialogue: 0,0:24:23.34,0:24:26.76,Default,,0000,0000,0000,,and he's got a little purple stub on it right there.And,of course,
Dialogue: 0,0:24:26.76,0:24:31.08,Default,,0000,0000,0000,,it's all being pulled away by the same idea,by the centrosomes.
Dialogue: 0,0:24:31.08,0:24:33.07,Default,,0000,0000,0000,,I want to make sure I get that word right.
Dialogue: 0,0:24:33.07,0:24:35.81,Default,,0000,0000,0000,,I'm afraid whether I used centromeres
Dialogue: 0,0:24:35.81,0:24:37.33,Default,,0000,0000,0000,,for the whole first part of the video,
Dialogue: 0,0:24:37.33,0:24:40.63,Default,,0000,0000,0000,,but hopefully,my confusion will help you from getting confused
Dialogue: 0,0:24:40.63,0:24:44.05,Default,,0000,0000,0000,,because you'll realize that it's a pitfall to fall into.
Dialogue: 0,0:24:44.05,0:24:46.67,Default,,0000,0000,0000,,So that's anaphase.Everything is getting pulled apart.
Dialogue: 0,0:24:46.67,0:24:49.08,Default,,0000,0000,0000,,And then you can imagine what telophase II is.
Dialogue: 0,0:24:49.08,0:24:51.00,Default,,0000,0000,0000,,In fact,I won't even redraw it.
Dialogue: 0,0:24:51.00,0:24:54.85,Default,,0000,0000,0000,,Telophase II,these things get pulled apart even more,
Dialogue: 0,0:24:54.85,0:24:59.01,Default,,0000,0000,0000,,so this is telophase II.
Dialogue: 0,0:24:59.01,0:25:02.01,Default,,0000,0000,0000,,They get pulled apart even more.The cell elongates.
Dialogue: 0,0:25:02.01,0:25:09.01,Default,,0000,0000,0000,,You start having this cleavage occur right here.
Dialogue: 0,0:25:09.01,0:25:11.37,Default,,0000,0000,0000,,So at the same time that in telophase II these get pulled part,
Dialogue: 0,0:25:11.37,0:25:13.05,Default,,0000,0000,0000,,you have the cytokinesis.
Dialogue: 0,0:25:13.05,0:25:15.21,Default,,0000,0000,0000,,The tubules start disintegrating
Dialogue: 0,0:25:15.21,0:25:19.08,Default,,0000,0000,0000,,and then you have a nucleus that forms around these.
Dialogue: 0,0:25:19.08,0:25:22.07,Default,,0000,0000,0000,,So what is the end result of all of these?
Dialogue: 0,0:25:22.07,0:25:27.46,Default,,0000,0000,0000,,Well,that guy's going to turn into a nucleus
Dialogue: 0,0:25:27.46,0:25:31.89,Default,,0000,0000,0000,,that has this purple dude with a little green stub,
Dialogue: 0,0:25:31.89,0:25:38.04,Default,,0000,0000,0000,,and then a long green guy,and then he's got his nuclear membrane.
Dialogue: 0,0:25:38.04,0:25:43.02,Default,,0000,0000,0000,,And,of course,there's the entire cytoplasm in the rest of the cell.
Dialogue: 0,0:25:43.02,0:25:47.21,Default,,0000,0000,0000,,The other person that was his kind of partner in this meiosis II,
Dialogue: 0,0:25:47.21,0:25:55.59,Default,,0000,0000,0000,,he's going to have a short purple and a long green.
Dialogue: 0,0:25:55.59,0:25:58.33,Default,,0000,0000,0000,,He has a nuclear membrane,and,
Dialogue: 0,0:25:58.33,0:26:03.03,Default,,0000,0000,0000,,of course,it has cytoplasm around it.
Dialogue: 0,0:26:03.03,0:26:05.79,Default,,0000,0000,0000,,And then on this side,you have something similar happening.
Dialogue: 0,0:26:05.79,0:26:07.72,Default,,0000,0000,0000,,You see this first guy,
Dialogue: 0,0:26:07.72,0:26:11.08,Default,,0000,0000,0000,,this first one right here has two long purple ones.
Dialogue: 0,0:26:11.08,0:26:13.00,Default,,0000,0000,0000,,They get separated.
Dialogue: 0,0:26:13.00,0:26:15.27,Default,,0000,0000,0000,,So let me see,you have one long purple in that cell
Dialogue: 0,0:26:15.27,0:26:19.06,Default,,0000,0000,0000,,and you have another long purple in this cell.
Dialogue: 0,0:26:19.06,0:26:21.82,Default,,0000,0000,0000,,In that top one,you have a short green one,
Dialogue: 0,0:26:21.82,0:26:23.99,Default,,0000,0000,0000,,and in this bottom,you have a short green one
Dialogue: 0,0:26:23.99,0:26:27.05,Default,,0000,0000,0000,,that had got a little bit of one of my dad's--
Dialogue: 0,0:26:27.05,0:26:30.05,Default,,0000,0000,0000,,a homologous part of one of my dad's chromosomes on it.
Dialogue: 0,0:26:30.05,0:26:34.42,Default,,0000,0000,0000,,And,of course,these also have nuclear membranes, nuclear membranes,
Dialogue: 0,0:26:34.42,0:26:38.26,Default,,0000,0000,0000,,and,of course,it has a cytoplasm in the rest of the cell,
Dialogue: 0,0:26:38.26,0:26:41.01,Default,,0000,0000,0000,,which we'll learn more about all those other things.
Dialogue: 0,0:26:41.01,0:26:42.47,Default,,0000,0000,0000,,So what we see here is that
Dialogue: 0,0:26:42.47,0:26:46.05,Default,,0000,0000,0000,,we went from a diploid starting way--where did we start?
Dialogue: 0,0:26:46.05,0:26:50.08,Default,,0000,0000,0000,,We started up here with a diploid germ cell,
Dialogue: 0,0:26:50.08,0:26:52.58,Default,,0000,0000,0000,,and we went through two stages of division.
Dialogue: 0,0:26:52.58,0:26:55.52,Default,,0000,0000,0000,,The first stage split up homologous pairs,
Dialogue: 0,0:26:55.53,0:26:57.85,Default,,0000,0000,0000,,but it started over with that crossing over,
Dialogue: 0,0:26:57.86,0:27:00.50,Default,,0000,0000,0000,,that genetic combination,which is a key feature of meiosis,
Dialogue: 0,0:27:00.50,0:27:05.06,Default,,0000,0000,0000,,which adds a lot a variation to a species or to a gene pool.
Dialogue: 0,0:27:05.06,0:27:08.76,Default,,0000,0000,0000,,And then the second phase separated the sister chromatids,
Dialogue: 0,0:27:08.76,0:27:11.59,Default,,0000,0000,0000,,just like what happens in mitosis.
Dialogue: 0,0:27:11.59,0:27:15.13,Default,,0000,0000,0000,,And we end up with four haploid cells
Dialogue: 0,0:27:15.13,0:27:18.05,Default,,0000,0000,0000,,because they have half the contingency of chromosomes,
Dialogue: 0,0:27:18.05,0:27:22.04,Default,,0000,0000,0000,,and these are called gametes.