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Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 0 00:00:00,804 --> 00:00:02,610 ERIC S. LANDER: Now, what happens to Mendel? 1 00:00:02,610 --> 00:00:04,630 Mendel makes this amazing discovery. 2 00:00:04,630 --> 00:00:06,660 He produces this great paper. 3 00:00:10,340 --> 00:00:12,980 Mendel never writes an amazing paper again. 4 00:00:12,980 --> 00:00:17,440 His entire scientific reputation hangs on this 1865 paper. 5 00:00:17,440 --> 00:00:20,890 He ends up working on another plant, a hawkweed that turns out to be a very 6 00:00:20,890 --> 00:00:22,500 unfortunate experimental choice. 7 00:00:22,500 --> 00:00:24,170 It has a lot of weird properties. 8 00:00:24,170 --> 00:00:25,700 And he can't ever make sense of it. 9 00:00:25,700 --> 00:00:29,960 And what Mendel does, because he's so successful, is Mendel gets promoted to 10 00:00:29,960 --> 00:00:34,500 be the abbot of the monastery, becomes consumed with administration and never 11 00:00:34,500 --> 00:00:37,940 really writes another great scientific paper, although he studies meteorology 12 00:00:37,940 --> 00:00:39,010 and other things like that. 13 00:00:39,010 --> 00:00:41,970 But that's pretty much it for Mendel's career. 14 00:00:41,970 --> 00:00:43,680 Mendel passes away. 15 00:00:43,680 --> 00:00:47,370 And this Mendel stuff is kind of largely forgotten. 16 00:00:51,990 --> 00:00:55,460 And the 1800s roll along. 17 00:00:55,460 --> 00:00:58,280 And an entirely different line of work appears. 18 00:00:58,280 --> 00:01:00,560 The entirely different line of work-- 19 00:01:00,560 --> 00:01:02,065 section five now-- 20 00:01:04,590 --> 00:01:13,740 cytology, cells in microscopes, people studying cells in microscopes. 21 00:01:13,740 --> 00:01:17,970 Well, microscopes had been invented long before. 22 00:01:17,970 --> 00:01:24,390 But when you looked under a microscope at cells, you could see all sorts of 23 00:01:24,390 --> 00:01:27,600 interesting structures, all sorts of interesting shapes 24 00:01:27,600 --> 00:01:30,000 and things like that. 25 00:01:30,000 --> 00:01:35,090 But what really began to make cytology interesting was the 26 00:01:35,090 --> 00:01:36,745 German chemical industry. 27 00:01:36,745 --> 00:01:40,770 The German chemical industry began inventing dyes, dyes 28 00:01:40,770 --> 00:01:42,550 you could stain things. 29 00:01:42,550 --> 00:01:47,070 And somebody thought to put dyes on cells. 30 00:01:47,070 --> 00:01:48,370 And they put dyes on cells. 31 00:01:48,370 --> 00:01:55,100 And what they found was that in the nucleus of a cell at certain times, 32 00:01:55,100 --> 00:02:05,540 dyes would stick to certain structures that look like these things, these 33 00:02:05,540 --> 00:02:09,389 some kind of bodies there. 34 00:02:09,389 --> 00:02:13,460 And these colored things were really interesting. 35 00:02:13,460 --> 00:02:15,550 And they had no idea what they were. 36 00:02:18,360 --> 00:02:21,653 And what do you do in science when you have no idea what something is? 37 00:02:21,653 --> 00:02:22,640 STUDENT: Poke at it. 38 00:02:22,640 --> 00:02:23,330 ERIC S. LANDER: You poke at it. 39 00:02:23,330 --> 00:02:24,685 But the problem is, you're going to poke in the microscope 40 00:02:24,685 --> 00:02:26,340 there and mess it up. 41 00:02:26,340 --> 00:02:33,280 Now, in order to make yourself feel better, you give it a name, because if 42 00:02:33,280 --> 00:02:36,000 you give a name, you're in control over it. 43 00:02:36,000 --> 00:02:39,560 The only thing they knew about these colored bodies were that they were 44 00:02:39,560 --> 00:02:41,070 colored bodies. 45 00:02:41,070 --> 00:02:46,290 And so they called them chromosomes, meaning colored things. 46 00:02:51,180 --> 00:02:53,010 That's what it means. 47 00:02:53,010 --> 00:02:54,900 Chromosome means colored thing. 48 00:02:54,900 --> 00:02:57,810 So they found these chromosomes. 49 00:02:57,810 --> 00:03:02,740 And they didn't know what these chromosomes were doing. 50 00:03:02,740 --> 00:03:08,660 But they made observations of cells at many points of their cell division. 51 00:03:08,660 --> 00:03:12,060 It turns out, in the 1800s, could not take movies. 52 00:03:12,060 --> 00:03:16,480 But they inferred by looking at cells at many times that these chromosomes 53 00:03:16,480 --> 00:03:19,140 underwent a remarkable choreography. 54 00:03:19,140 --> 00:03:22,580 They did a dance during cell division. 55 00:03:22,580 --> 00:03:26,280 And for you, let's show a movie of what that looks like. 56 00:03:26,280 --> 00:03:30,740 Let's get a black and white movie of a plant cell here-- fire away. 57 00:03:30,740 --> 00:03:32,640 These are these colored things. 58 00:03:32,640 --> 00:03:33,400 We don't have it in color. 59 00:03:33,400 --> 00:03:34,190 It's a black and white picture. 60 00:03:34,190 --> 00:03:36,310 Just look what they're doing as the cell is under-- 61 00:03:36,310 --> 00:03:39,690 this is a lily of some sort, I think. 62 00:03:39,690 --> 00:03:41,950 And it's undergoing division, this cell. 63 00:03:41,950 --> 00:03:44,480 And look at this, they're moving around. 64 00:03:44,480 --> 00:03:45,730 They're moving around. 65 00:03:45,730 --> 00:03:47,390 They're arranging themselves. 66 00:03:47,390 --> 00:03:50,690 They're getting organized in some way. 67 00:03:50,690 --> 00:03:51,400 There we go. 68 00:03:51,400 --> 00:03:53,540 They're getting organized. 69 00:03:53,540 --> 00:03:56,220 Whoa. 70 00:03:56,220 --> 00:03:58,330 Check that out. 71 00:03:58,330 --> 00:04:04,620 Every one of them split, goes apart, and there you go. 72 00:04:04,620 --> 00:04:05,610 How interesting. 73 00:04:05,610 --> 00:04:07,310 Let's pull up another quick movie. 74 00:04:07,310 --> 00:04:09,630 Let's pull up a movie of a sea urchin. 75 00:04:09,630 --> 00:04:11,010 Check out this sea urchin here. 76 00:04:15,240 --> 00:04:15,900 Here we go. 77 00:04:15,900 --> 00:04:17,150 It'll go really quickly. 78 00:04:19,015 --> 00:04:19,959 Whoop-- 79 00:04:19,959 --> 00:04:22,890 chromosomes going away. 80 00:04:22,890 --> 00:04:26,700 Let's pull up a frog embryo. 81 00:04:26,700 --> 00:04:28,375 Check out the frog embryo here. 82 00:04:32,850 --> 00:04:34,070 Check out those chromosomes. 83 00:04:34,070 --> 00:04:36,420 Tell me what you see here. 84 00:04:36,420 --> 00:04:37,540 And they're coming together. 85 00:04:37,540 --> 00:04:38,380 They're coming together. 86 00:04:38,380 --> 00:04:40,120 They're getting them all organized. 87 00:04:40,120 --> 00:04:40,550 Look at that. 88 00:04:40,550 --> 00:04:42,070 Oh, but there's a straggler. 89 00:04:42,070 --> 00:04:43,150 There's the straggler here. 90 00:04:43,150 --> 00:04:45,700 We're going to wait for the straggler. 91 00:04:45,700 --> 00:04:49,160 I'm waiting for the straggler. 92 00:04:49,160 --> 00:04:50,225 There we go. 93 00:04:50,225 --> 00:04:56,760 The straggler gets in there, and now it's ready to go. 94 00:04:56,760 --> 00:05:03,650 There we go, pulls back, divides, two cells. 95 00:05:03,650 --> 00:05:07,050 Not only do they organize themselves beautifully, but they even had the 96 00:05:07,050 --> 00:05:12,770 good courtesy to wait for the last chromosome to join. 97 00:05:12,770 --> 00:05:17,120 It is incredibly polite choreography. 98 00:05:17,120 --> 00:05:22,610 This was cell division, typical cell division called mitosis. 99 00:05:22,610 --> 00:05:24,120 What's going on here in mitosis? 100 00:05:27,490 --> 00:05:29,060 So in mitosis-- 101 00:05:29,060 --> 00:05:34,660 now, from those gorgeous pictures, it's not so obvious how to follow 102 00:05:34,660 --> 00:05:35,330 everything. 103 00:05:35,330 --> 00:05:38,440 It took people a long time to figure out what was going on. 104 00:05:38,440 --> 00:05:43,890 And what the picture ends up looking like is something like this. 105 00:05:43,890 --> 00:05:51,700 That chromosomes, which we saw were going to split apart, really have two 106 00:05:51,700 --> 00:05:53,700 copies of something. 107 00:05:53,700 --> 00:06:02,090 And they're lining up along the middle of the cell. 108 00:06:02,090 --> 00:06:05,010 Take some interpretation to say this here. 109 00:06:05,010 --> 00:06:10,420 But it looks like they're lining up across the middle of the cell. 110 00:06:10,420 --> 00:06:16,520 When they've got themselves all perfectly lined up like that, they 111 00:06:16,520 --> 00:06:19,470 pull back and split apart. 112 00:06:23,630 --> 00:06:24,500 That's it. 113 00:06:24,500 --> 00:06:24,930 Yes? 114 00:06:24,930 --> 00:06:28,580 STUDENT: How accelerated was the video we were watching, or slowed down? 115 00:06:28,580 --> 00:06:30,800 ERIC S. LANDER: A fair amount accelerated. 116 00:06:30,800 --> 00:06:34,590 A fair amount accelerated, because we have a limited time in the class. 117 00:06:34,590 --> 00:06:37,590 So it's time lapse photography. 118 00:06:37,590 --> 00:06:38,880 That's right. 119 00:06:38,880 --> 00:06:40,720 So pretty easy. 120 00:06:40,720 --> 00:06:42,585 These things, somehow there were two of them. 121 00:06:42,585 --> 00:06:44,470 You saw how they split apart, right? 122 00:06:44,470 --> 00:06:47,930 When they split apart, there's singletons, but they must, at the time 123 00:06:47,930 --> 00:06:52,930 they appeared there look like a little x held together in the middle, because 124 00:06:52,930 --> 00:06:54,890 there were two copies of this thing. 125 00:06:54,890 --> 00:06:59,960 And by the way, after this movie, the chromosomes seem to disappear. 126 00:06:59,960 --> 00:07:03,060 And then they come back and re-condense, reappear. 127 00:07:03,060 --> 00:07:06,960 So they condense nicely into these shapes but then seem to go away. 128 00:07:06,960 --> 00:07:08,600 They're still there, but you don't see them. 129 00:07:08,600 --> 00:07:10,230 And they come back and they condense. 130 00:07:10,230 --> 00:07:14,160 And when they condense, the next time they'll have these two copies again. 131 00:07:14,160 --> 00:07:19,710 So somehow they've been duplicated while you're not watching. 132 00:07:19,710 --> 00:07:20,960 That was mitosis. 133 00:07:22,860 --> 00:07:26,690 But there was something else kind of interesting, which was when cells 134 00:07:26,690 --> 00:07:32,930 didn't just divide in their normal way, but cells divided to make 135 00:07:32,930 --> 00:07:38,910 gametes, say, like sperm or eggs, the cells that undergo fertilization. 136 00:07:38,910 --> 00:07:43,722 To make gametes, a very different picture emerged. 137 00:07:43,722 --> 00:07:55,630 The very different picture was that in meiosis, meiosis here, the chromosomes 138 00:07:55,630 --> 00:07:56,880 line up differently. 139 00:08:00,910 --> 00:08:07,570 Instead of the Xs, two copies of the same chromosome lining up like that 140 00:08:07,570 --> 00:08:12,340 all down the middle, it'll line up like this. 141 00:08:12,340 --> 00:08:14,830 I'll make a little chromosome here. 142 00:08:14,830 --> 00:08:16,750 And its little partner is over here. 143 00:08:21,590 --> 00:08:30,370 And the first meiotic division, meiosis number one, did not split 144 00:08:30,370 --> 00:08:32,140 apart the Xs. 145 00:08:32,140 --> 00:08:39,850 What it does is, it gives rise to two cells, each of which gets one 146 00:08:39,850 --> 00:08:43,120 copy of each pair. 147 00:08:43,120 --> 00:08:48,920 Then, in meiosis two-- 148 00:08:48,920 --> 00:08:52,700 here's my little chromosome and my big chromosome. 149 00:08:52,700 --> 00:08:55,080 Just for the sake of argument, I'll call that one chromosome one and 150 00:08:55,080 --> 00:08:57,050 chromosome two. 151 00:08:57,050 --> 00:08:59,280 We've got chromosome one here, chromosome two. 152 00:08:59,280 --> 00:09:00,530 So we've got this. 153 00:09:06,660 --> 00:09:20,200 In the second meiotic division, meiosis two, now it undergoes a 154 00:09:20,200 --> 00:09:23,040 division that looks for all the world just like mitosis. 155 00:09:25,940 --> 00:09:30,450 And it gives rise now to that. 156 00:09:40,560 --> 00:09:42,790 That's it. 157 00:09:42,790 --> 00:09:43,840 So there's a big difference. 158 00:09:43,840 --> 00:09:47,490 What's the big difference here? 159 00:09:47,490 --> 00:09:54,420 Up there, there were four chromosomes or two pairs of chromosomes. 160 00:09:54,420 --> 00:09:56,220 They split. 161 00:09:56,220 --> 00:09:58,060 And you still have those four chromosomes. 162 00:09:58,060 --> 00:10:00,410 Here, I've only got two. 163 00:10:00,410 --> 00:10:07,910 They came in pairs and each offspring cell at the end of this process gets 164 00:10:07,910 --> 00:10:10,700 one of the two. 165 00:10:10,700 --> 00:10:11,570 Let's look over here. 166 00:10:11,570 --> 00:10:12,240 Mitosis-- 167 00:10:12,240 --> 00:10:14,930 bring up my mitosis a second if you would. 168 00:10:14,930 --> 00:10:20,310 In mitosis, we have our homologs, meaning the two copies of a given 169 00:10:20,310 --> 00:10:21,330 chromosome. 170 00:10:21,330 --> 00:10:24,120 Each chromosome, they come in pairs here. 171 00:10:24,120 --> 00:10:26,880 They each split. 172 00:10:26,880 --> 00:10:30,510 Now, this picture here doesn't have them lined up nicely over each other 173 00:10:30,510 --> 00:10:31,610 like I did. 174 00:10:31,610 --> 00:10:35,790 But this is one chromosome, the other chromosome, and here are the Xs. 175 00:10:35,790 --> 00:10:38,150 I drew them lined up over on top of each other. 176 00:10:38,150 --> 00:10:39,930 But you can draw them any way you want to. 177 00:10:39,930 --> 00:10:41,680 And they get tugged. 178 00:10:41,680 --> 00:10:45,180 One of the two pieces gets tugged here. 179 00:10:45,180 --> 00:10:47,350 And the other piece gets tugged here. 180 00:10:47,350 --> 00:10:52,770 And you end up here with, the original chromosomes were 181 00:10:52,770 --> 00:10:56,230 duplicated, were separated. 182 00:10:56,230 --> 00:10:58,320 And it gets back to its initial state. 183 00:10:58,320 --> 00:10:59,270 That's mitosis. 184 00:10:59,270 --> 00:11:03,420 But in meiosis, we have an extra step. 185 00:11:03,420 --> 00:11:06,050 Chromosomes here-- 186 00:11:06,050 --> 00:11:08,350 here, we're now just showing this pair. 187 00:11:08,350 --> 00:11:10,880 They get pulled over. 188 00:11:10,880 --> 00:11:15,105 And then secondarily, they undergo this separate division. 189 00:11:18,790 --> 00:11:22,910 So now, what does that tell us? 190 00:11:22,910 --> 00:11:26,140 Chromosomes come in pairs. 191 00:11:26,140 --> 00:11:30,660 This chromosome thing was found in 1889, 1890, actually, just about the 192 00:11:30,660 --> 00:11:33,200 time Buchner is working in his lab. 193 00:11:33,200 --> 00:11:36,620 Same time people are discovering chromosomes, and they're working out 194 00:11:36,620 --> 00:11:41,860 this choreography that says, when gametes are made, when you make sperm 195 00:11:41,860 --> 00:11:46,560 or eggs, something occurs in pairs. 196 00:11:46,560 --> 00:11:51,180 And one copy of each pair randomly goes to the daughter cell. 197 00:11:55,560 --> 00:11:58,500 And just about that time-- 198 00:11:58,500 --> 00:12:01,600 1900 actually, January of 1900-- 199 00:12:01,600 --> 00:12:06,930 people begin to redo the heredity experiments and rediscover and 200 00:12:06,930 --> 00:12:09,540 re-appreciate Mendel. 201 00:12:09,540 --> 00:12:11,250 Mendel is getting rediscovered. 202 00:12:11,250 --> 00:12:16,770 And the chromosome choreography is being worked out. 203 00:12:16,770 --> 00:12:22,430 And by 1902, someone says, wait a second, this idea that Mendel had of 204 00:12:22,430 --> 00:12:28,090 discrete particles of inheritance coming in pairs and going randomly, 205 00:12:28,090 --> 00:12:34,000 and these chromosomes coming in pairs and distributing randomly. 206 00:12:34,000 --> 00:12:36,260 Oh, we don't have to think abstractly anymore. 207 00:12:36,260 --> 00:12:37,470 That was a problem with Mendel. 208 00:12:37,470 --> 00:12:39,020 It was all so abstract. 209 00:12:39,020 --> 00:12:40,670 We didn't know what a gene was. 210 00:12:40,670 --> 00:12:46,300 It must be that these chromosomes are genes or carry genes or have something 211 00:12:46,300 --> 00:12:50,070 to do with genes because they have the same choreography. 212 00:12:50,070 --> 00:12:57,840 And so the idea starts floating around in 1902 that chromosomes must be the 213 00:12:57,840 --> 00:12:59,435 basis of heredity. 214 00:12:59,435 --> 00:13:02,940 It's controversial, but it's beginning to catch on. 215 00:13:02,940 --> 00:13:06,620 What a beautiful, beautiful idea-- 216 00:13:06,620 --> 00:13:09,040 the Chromosome Theory of Inheritance. 217 00:13:14,410 --> 00:13:18,650 That here is the physical manifestation of Mendel's abstract 218 00:13:18,650 --> 00:13:30,940 genes, that when chromosomes line up, maybe this chromosome has the 219 00:13:30,940 --> 00:13:33,200 roundness gene. 220 00:13:33,200 --> 00:13:36,400 And let's see, this copy of the chromosome has been duplicated, but 221 00:13:36,400 --> 00:13:38,190 it's got the big Rs. 222 00:13:38,190 --> 00:13:40,860 And that guy there has got the little rs. 223 00:13:40,860 --> 00:13:47,520 And this chromosome over here, it's got the big G on it. 224 00:13:47,520 --> 00:13:49,820 That's the big G carrying chromosome. 225 00:13:49,820 --> 00:13:57,030 And over here, this chromosome, it's got the little g. 226 00:13:57,030 --> 00:14:01,190 And not only do the big Rs and little rs go randomly, one to each daughter 227 00:14:01,190 --> 00:14:06,530 cell, and the big Gs and little gs go randomly, one to each daughter cell, 228 00:14:06,530 --> 00:14:12,350 but there's no correlation between the big Rs and the big Gs, because they're 229 00:14:12,350 --> 00:14:13,600 on different chromosomes. 230 00:14:16,090 --> 00:14:18,660 So that explains Mendel's second law. 231 00:14:18,660 --> 00:14:23,160 Mendel's second law is perfectly explained by the chromosome theory, 232 00:14:23,160 --> 00:14:25,710 because if the genes are on different chromosomes, they're getting assorted 233 00:14:25,710 --> 00:14:28,050 independently. 234 00:14:28,050 --> 00:14:30,670 It's beautiful. 235 00:14:30,670 --> 00:14:31,920 But there's a problem. 236 00:14:34,730 --> 00:14:37,013 How many traits did Mendel study? 237 00:14:37,013 --> 00:14:37,740 STUDENT: Seven. 238 00:14:37,740 --> 00:14:38,990 ERIC S. LANDER: Seven. 239 00:14:41,550 --> 00:14:46,550 How many pairs of chromosomes do peas have? 240 00:14:46,550 --> 00:14:49,915 No reason you should know, but the answer is seven. 241 00:14:53,760 --> 00:14:57,570 What if Mendel had studied an eighth trait? 242 00:14:57,570 --> 00:15:01,650 Could it have been on a different chromosome? 243 00:15:01,650 --> 00:15:04,360 There aren't eight chromosomes. 244 00:15:04,360 --> 00:15:10,710 It would have to be that eighth trait on the same chromosome, if this theory 245 00:15:10,710 --> 00:15:14,600 is right, as one of the existing traits. 246 00:15:14,600 --> 00:15:18,620 Then how could it be assorting independently? 247 00:15:18,620 --> 00:15:20,290 Because it's going to be on the same chromosome. 248 00:15:23,190 --> 00:15:26,310 That's going to be correlated. 249 00:15:26,310 --> 00:15:29,960 So either Mendel's Law of Inheritance, his Second Law of Inheritance of 250 00:15:29,960 --> 00:15:35,710 independent assortment is wrong, or this chromosome theory is wrong. 251 00:15:35,710 --> 00:15:37,840 You can't have them both. 252 00:15:37,840 --> 00:15:39,010 So who is it? 253 00:15:39,010 --> 00:15:43,630 Mendel wrong, or the Chromosome Theory wrong? 254 00:15:43,630 --> 00:15:46,270 Unfortunately, we don't have enough time for it in today's lecture. 255 00:15:46,270 --> 00:15:49,260 So next time, we're going to find out who's right. 256 00:15:51,850 --> 00:15:54,150 Before we go on to, take a moment. 257 00:15:54,150 --> 00:15:56,905 We've got a question for you about the number of chromosomes that are found 258 00:15:56,905 --> 00:15:58,155 in gametes. 20105

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