1 00:00:16,401 --> 00:00:19,270 ADAM MARTIN: Well, first of all, nice job on the exam. 2 00:00:19,270 --> 00:00:22,440 We were quite pleased with how you guys did. 3 00:00:22,440 --> 00:00:24,630 And so from now on in the course, 4 00:00:24,630 --> 00:00:26,910 Professor Imperiali has been telling you 5 00:00:26,910 --> 00:00:32,759 about information flow, but information flow within itself, 6 00:00:32,759 --> 00:00:37,770 so information flow from the DNA to the proteins that 7 00:00:37,770 --> 00:00:43,530 are made in the cell, which determines what that cell does. 8 00:00:43,530 --> 00:00:46,450 And so we're going to switch directions today. 9 00:00:46,450 --> 00:00:49,080 And we're going to start talking about how information 10 00:00:49,080 --> 00:00:52,680 flows between cells-- 11 00:00:52,680 --> 00:00:55,740 so from a parent cell to its daughter cells. 12 00:00:55,740 --> 00:00:59,160 And we're also going to talk about how information flows 13 00:00:59,160 --> 00:01:02,280 from generation to the next. 14 00:01:02,280 --> 00:01:06,810 And this, of course, is the study of genetics. 15 00:01:12,030 --> 00:01:15,360 And what genetics is as a discipline is it 16 00:01:15,360 --> 00:01:22,380 is the study of genes and their inheritance. 17 00:01:29,060 --> 00:01:33,570 And the genes that you inherit influences what 18 00:01:33,570 --> 00:01:35,340 is known as your phenotype. 19 00:01:41,760 --> 00:01:44,550 And what phenotype is is simply the set 20 00:01:44,550 --> 00:01:47,490 of traits that define you. 21 00:01:47,490 --> 00:01:52,455 So you can think of it as a set of observable traits. 22 00:02:00,330 --> 00:02:03,480 And this involves your genes, as you probably know. 23 00:02:03,480 --> 00:02:06,900 I mean, just this morning, I was dropping my son off at school, 24 00:02:06,900 --> 00:02:10,770 and he was comparing how tall he was compared to his classmates. 25 00:02:10,770 --> 00:02:14,880 And as he went in, he was like, thanks for the genes, dad. 26 00:02:14,880 --> 00:02:18,180 So I expect that many of you are going 27 00:02:18,180 --> 00:02:21,000 to be familiar with much of what we'll discuss, 28 00:02:21,000 --> 00:02:23,640 but we're going to lay a real solid foundation, 29 00:02:23,640 --> 00:02:27,150 because it's really fundamental for understanding 30 00:02:27,150 --> 00:02:32,760 the rules of inheritance and how that works. 31 00:02:32,760 --> 00:02:35,890 So genetics is the study of genes. 32 00:02:35,890 --> 00:02:39,040 So what is a gene? 33 00:02:39,040 --> 00:02:42,640 You can think about genes in different ways. 34 00:02:42,640 --> 00:02:45,370 And what we've been talking about up until now, 35 00:02:45,370 --> 00:02:48,120 we've been talking about molecular biology and what 36 00:02:48,120 --> 00:02:49,925 is known as the central dogma. 37 00:02:56,700 --> 00:03:03,840 And the central dogma states that the source of the code 38 00:03:03,840 --> 00:03:05,550 is in the DNA. 39 00:03:05,550 --> 00:03:09,540 And there's an information flow from a piece of DNA, 40 00:03:09,540 --> 00:03:11,110 which is a gene. 41 00:03:11,110 --> 00:03:13,050 And the gene is a piece of DNA that 42 00:03:13,050 --> 00:03:17,790 then encodes some sort of RNA, such as a messenger RNA. 43 00:03:17,790 --> 00:03:21,930 And many of these RNAs can make specific proteins 44 00:03:21,930 --> 00:03:26,190 that do things in your cells in your body. 45 00:03:26,190 --> 00:03:29,820 So that's one very molecular picture of a gene. 46 00:03:29,820 --> 00:03:35,130 You can think of a gene as a string of nucleotides. 47 00:03:35,130 --> 00:03:39,540 And there might be a reading frame in those nucleotides that 48 00:03:39,540 --> 00:03:42,450 encodes a protein. 49 00:03:42,450 --> 00:03:45,900 So that's a very molecular picture of a gene. 50 00:03:45,900 --> 00:03:51,180 The field of genetics started well before we knew about DNA, 51 00:03:51,180 --> 00:03:55,950 and its importance, and what the DNA encoded 52 00:03:55,950 --> 00:03:57,960 RNA which encoded proteins. 53 00:03:57,960 --> 00:04:01,590 So the concept of a gene is much older than that. 54 00:04:01,590 --> 00:04:05,130 And so another way you can think of a gene 55 00:04:05,130 --> 00:04:08,190 is it's essentially the functional unit of heredity. 56 00:04:11,530 --> 00:04:16,170 So it's the functional unit of heredity. 57 00:04:22,160 --> 00:04:23,400 I'll bump this up. 58 00:04:31,210 --> 00:04:33,850 So I want to just briefly pause and kind of give you 59 00:04:33,850 --> 00:04:38,020 an overview of why I think genetics is so important. 60 00:04:38,020 --> 00:04:41,200 So what you saw up here is you saw a cell divide. 61 00:04:41,200 --> 00:04:43,600 And I showed you this in the last lecture-- 62 00:04:43,600 --> 00:04:46,780 you saw the chromosomes, which are here, 63 00:04:46,780 --> 00:04:48,850 how they're segregated to different daughters. 64 00:04:48,850 --> 00:04:52,180 And this is-- basically, you're seeing the information flow 65 00:04:52,180 --> 00:04:55,600 from the parent cell into the daughter herself. 66 00:04:55,600 --> 00:04:58,600 But we saw this, so I'm just going to skip ahead. 67 00:04:58,600 --> 00:05:02,020 So why is this so important? 68 00:05:02,020 --> 00:05:05,050 I'm going to give you a fairly grandiose view of why 69 00:05:05,050 --> 00:05:07,390 genetics is so important. 70 00:05:07,390 --> 00:05:11,020 And I'm going to say that we can make a good argument 71 00:05:11,020 --> 00:05:15,430 that genetics is responsible for the rise 72 00:05:15,430 --> 00:05:16,810 of modern civilization. 73 00:05:20,170 --> 00:05:26,410 Humans, as a species, began manipulating genes and genetics 74 00:05:26,410 --> 00:05:29,440 even before we had any understanding of what 75 00:05:29,440 --> 00:05:30,230 was going on. 76 00:05:30,230 --> 00:05:33,400 So this is more of an unconscious selection. 77 00:05:33,400 --> 00:05:38,560 And so 10,000 years ago, humans were hunter gatherers. 78 00:05:38,560 --> 00:05:41,830 They'd go out, and try to find nuts and seeds, and hunt 79 00:05:41,830 --> 00:05:42,370 animals. 80 00:05:42,370 --> 00:05:44,410 And that's how we got our food. 81 00:05:44,410 --> 00:05:48,190 But around 10,000 years ago was the first example 82 00:05:48,190 --> 00:05:51,370 of where humans, as a species, really 83 00:05:51,370 --> 00:05:55,960 altered the phenotype of a plant, in this case. 84 00:05:55,960 --> 00:06:00,740 So wild wheat and wild barley, the seeds develop in a pod. 85 00:06:00,740 --> 00:06:02,740 And the biology of the wild wheat 86 00:06:02,740 --> 00:06:05,650 is such that the pod shatters, and the seeds then 87 00:06:05,650 --> 00:06:08,230 spread on the ground where they can then 88 00:06:08,230 --> 00:06:10,630 germinate into new plants. 89 00:06:10,630 --> 00:06:14,410 But 10,000 years ago, humans decided 90 00:06:14,410 --> 00:06:18,880 that it would be more ideal if we had a form of wheat which 91 00:06:18,880 --> 00:06:22,300 didn't shatter, which is known as non-shattering wheat 92 00:06:22,300 --> 00:06:26,260 in which the seeds remain on the plant. 93 00:06:26,260 --> 00:06:28,930 And that allows it to be easily harvested 94 00:06:28,930 --> 00:06:30,970 at the end of the season. 95 00:06:30,970 --> 00:06:34,420 So 10,000 years ago is one of the first examples 96 00:06:34,420 --> 00:06:37,930 where humans really genetically altered 97 00:06:37,930 --> 00:06:39,430 the phenotype of a plant. 98 00:06:39,430 --> 00:06:42,490 And they selected for this non-shattering wheat, 99 00:06:42,490 --> 00:06:46,870 which then allowed for the rise of agriculture. 100 00:06:46,870 --> 00:06:51,480 In addition to wheat, we also-- 101 00:06:51,480 --> 00:06:54,790 about 4,000 years ago was the rise 102 00:06:54,790 --> 00:06:57,620 of domesticated fruit and nuts. 103 00:06:57,620 --> 00:06:58,900 So here are some almonds. 104 00:06:58,900 --> 00:07:02,350 If you would like an almond, feel free to have some. 105 00:07:02,350 --> 00:07:03,500 You guys want some almonds? 106 00:07:03,500 --> 00:07:04,000 No. 107 00:07:04,000 --> 00:07:05,750 If you have a nut allergy, don't eat them. 108 00:07:09,100 --> 00:07:10,060 Great. 109 00:07:10,060 --> 00:07:14,400 So wild almonds, when you chew them, 110 00:07:14,400 --> 00:07:16,120 there's an enzymatic reaction that 111 00:07:16,120 --> 00:07:19,840 results in cyanide forming. 112 00:07:19,840 --> 00:07:22,810 Rachel just stopped chewing. 113 00:07:22,810 --> 00:07:23,450 Don't worry. 114 00:07:23,450 --> 00:07:27,760 These are almonds that are harvested at Trader Joe's, so 115 00:07:27,760 --> 00:07:29,440 you're safe. 116 00:07:29,440 --> 00:07:32,920 And so the wild almonds, obviously, 117 00:07:32,920 --> 00:07:36,130 were not compatible for consumption. 118 00:07:36,130 --> 00:07:39,040 But 4,000 years ago, humans again 119 00:07:39,040 --> 00:07:41,710 selected for a form of the almond, which 120 00:07:41,710 --> 00:07:44,980 involved just a single gene, which was non-bitter 121 00:07:44,980 --> 00:07:50,290 and known as a sweet almond, which was also not toxic. 122 00:07:50,290 --> 00:07:54,760 So this doesn't just go for foods, but also for clothing. 123 00:07:54,760 --> 00:07:58,600 So humans have selected for cotton with long lint. 124 00:07:58,600 --> 00:08:03,100 And that served as a basis for clothing and sort 125 00:08:03,100 --> 00:08:06,010 of allowing us to have fabric. 126 00:08:06,010 --> 00:08:09,670 And I just want to end with a little story about the almond, 127 00:08:09,670 --> 00:08:12,550 which is part of the archaeological evidence 128 00:08:12,550 --> 00:08:15,100 for when almonds were domesticated 129 00:08:15,100 --> 00:08:18,280 was when King Tut's tomb was unearthed. 130 00:08:18,280 --> 00:08:20,800 And they found a pile of almonds next to the tomb, 131 00:08:20,800 --> 00:08:24,520 because the Egyptian culture, what they did 132 00:08:24,520 --> 00:08:28,180 is they buried the dead with food to sustain them 133 00:08:28,180 --> 00:08:30,160 in the afterlife. 134 00:08:30,160 --> 00:08:32,559 So that just gives you an idea as to how far 135 00:08:32,559 --> 00:08:36,280 back the importance of genetics goes. 136 00:08:36,280 --> 00:08:38,710 If we think about nowadays, right now 137 00:08:38,710 --> 00:08:43,090 you are always seeing genetics in the news. 138 00:08:43,090 --> 00:08:45,670 And you also have the opportunity 139 00:08:45,670 --> 00:08:50,530 yourself to sort of do your own genetic experiment. 140 00:08:50,530 --> 00:08:53,830 And so now you guys are undoubtedly 141 00:08:53,830 --> 00:08:56,140 aware of all these companies that 142 00:08:56,140 --> 00:08:58,042 want you to send them your DNA. 143 00:08:58,042 --> 00:08:59,500 And they also want you to send them 144 00:08:59,500 --> 00:09:03,160 money, such that they can give you information 145 00:09:03,160 --> 00:09:10,270 about your family tree and also information about your health. 146 00:09:10,270 --> 00:09:13,130 So this is now a big business. 147 00:09:13,130 --> 00:09:15,340 But if you don't understand genetics, 148 00:09:15,340 --> 00:09:20,000 this is not as useful as it could be. 149 00:09:20,000 --> 00:09:21,370 So I'm just curious. 150 00:09:21,370 --> 00:09:24,220 How many people here have used one of these services 151 00:09:24,220 --> 00:09:26,960 and had their DNA genotyped? 152 00:09:26,960 --> 00:09:27,950 Cool. 153 00:09:27,950 --> 00:09:30,390 And do you think that really changed 154 00:09:30,390 --> 00:09:32,640 your view of who you are? 155 00:09:32,640 --> 00:09:34,360 Or was it kind of, eh? 156 00:09:34,360 --> 00:09:36,390 AUDIENCE: We actually-- I don't know if we even 157 00:09:36,390 --> 00:09:37,598 looked at where we came from. 158 00:09:37,598 --> 00:09:39,792 We looked for genetic disease. 159 00:09:39,792 --> 00:09:42,000 ADAM MARTIN: So you're looking for genetic disorders. 160 00:09:42,000 --> 00:09:46,350 And you don't have to tell me anything about that. 161 00:09:46,350 --> 00:09:50,830 Yeah, so I have not done this, but my dad has done it. 162 00:09:50,830 --> 00:09:53,970 And he will go find his relatives 163 00:09:53,970 --> 00:09:55,770 and bore them with our ancestry. 164 00:09:59,190 --> 00:10:01,980 So this is one example of how genetics is really 165 00:10:01,980 --> 00:10:03,720 in play today. 166 00:10:03,720 --> 00:10:05,400 And not everyone knows how this works. 167 00:10:05,400 --> 00:10:08,550 I've had people at Starbucks in the morning come up 168 00:10:08,550 --> 00:10:14,130 to me with their 23andMe profile and ask me to explain stuff, 169 00:10:14,130 --> 00:10:16,330 because they know who I am. 170 00:10:16,330 --> 00:10:19,200 It's a little awkward. 171 00:10:19,200 --> 00:10:22,350 So we can also use genetics for forensics. 172 00:10:22,350 --> 00:10:25,230 And so this is kind of a-- 173 00:10:25,230 --> 00:10:28,500 I had a lab manager in the lab, and he told me 174 00:10:28,500 --> 00:10:32,370 that people were doing this in senior homes 175 00:10:32,370 --> 00:10:35,130 in Florida, which I thought was kind of funny. 176 00:10:35,130 --> 00:10:40,470 What I find hilarious about this is the mug shot of the dog. 177 00:10:40,470 --> 00:10:42,840 That dog looks so guilty. 178 00:10:42,840 --> 00:10:45,540 But you can use DNA to-- 179 00:10:45,540 --> 00:10:48,680 you can use DNA to genotype poop. 180 00:10:48,680 --> 00:10:50,580 You can genotype your neighbor's dog. 181 00:10:50,580 --> 00:10:53,280 You can get evidence that they're the one that's 182 00:10:53,280 --> 00:10:55,530 pooping on your lawn. 183 00:10:55,530 --> 00:10:57,930 So that's a not-so-serious example. 184 00:10:57,930 --> 00:11:01,740 But there are more serious examples 185 00:11:01,740 --> 00:11:05,310 of where DNA genotyping is really having 186 00:11:05,310 --> 00:11:07,200 an effect in our society. 187 00:11:07,200 --> 00:11:10,350 And this is something I mentioned in the intro lecture. 188 00:11:10,350 --> 00:11:14,580 Just this past spring, someone was 189 00:11:14,580 --> 00:11:18,360 suspected as being the Golden State Killer. 190 00:11:18,360 --> 00:11:19,710 This is a cold case. 191 00:11:19,710 --> 00:11:23,360 The killings happened 40 years ago, 192 00:11:23,360 --> 00:11:28,200 but the break came from investigators getting DNA 193 00:11:28,200 --> 00:11:31,740 from the suspect's relatives to implicate 194 00:11:31,740 --> 00:11:34,380 this person in this crime. 195 00:11:34,380 --> 00:11:36,480 So they had DNA from the crime. 196 00:11:36,480 --> 00:11:39,510 And they saw that there were matches to the DNA at the crime 197 00:11:39,510 --> 00:11:40,530 to certain people. 198 00:11:40,530 --> 00:11:42,870 And then they can reconstruct who 199 00:11:42,870 --> 00:11:47,400 might be the person in the right place to commit the crime. 200 00:11:47,400 --> 00:11:48,420 So this is-- 201 00:11:48,420 --> 00:11:50,340 I think this is interesting, because it also 202 00:11:50,340 --> 00:11:54,060 leads to all sorts of privacy issues, right? 203 00:11:54,060 --> 00:11:59,460 Who's going to gain access to your genotype 204 00:11:59,460 --> 00:12:02,460 if you submitted to these companies, right? 205 00:12:02,460 --> 00:12:04,490 I mean, this is probably a case where 206 00:12:04,490 --> 00:12:08,370 I'd argue there's probably a beneficial result in that you 207 00:12:08,370 --> 00:12:12,150 can actually figure out if someone's committed a crime. 208 00:12:12,150 --> 00:12:13,800 But there are other issues in terms 209 00:12:13,800 --> 00:12:15,990 of thinking about insurance companies 210 00:12:15,990 --> 00:12:22,800 where we might be interested in having our information not 211 00:12:22,800 --> 00:12:25,380 publicly available to insurance companies. 212 00:12:25,380 --> 00:12:28,020 And maybe this is something we can discuss later 213 00:12:28,020 --> 00:12:31,580 on in another lecture. 214 00:12:31,580 --> 00:12:34,260 For today, I want to move on and go through really 215 00:12:34,260 --> 00:12:36,690 the fundamentals of genetics. 216 00:12:36,690 --> 00:12:39,720 And what I'm going to do is I'm going to start with the answer. 217 00:12:39,720 --> 00:12:40,410 OK? 218 00:12:40,410 --> 00:12:42,780 I'm going to present to you guys today 219 00:12:42,780 --> 00:12:46,710 the physical model for how inheritance happens. 220 00:12:46,710 --> 00:12:47,700 OK? 221 00:12:47,700 --> 00:12:54,750 So today, we're going to go over the physical model 222 00:12:54,750 --> 00:12:55,860 of inheritance. 223 00:13:02,130 --> 00:13:05,920 And this physical model involves cell division, 224 00:13:05,920 --> 00:13:07,950 which you saw in the last lecture 225 00:13:07,950 --> 00:13:11,340 and also in my opening slide. 226 00:13:11,340 --> 00:13:15,060 It involves cell division and the physical segregation 227 00:13:15,060 --> 00:13:18,190 of the chromosomes during cell division. 228 00:13:18,190 --> 00:13:20,160 So also chromosome segregation. 229 00:13:30,800 --> 00:13:34,770 OK, so this is how I'm going to represent chromosomes. 230 00:13:34,770 --> 00:13:40,330 And I just want to step you through what it all means. 231 00:13:40,330 --> 00:13:44,460 So I have these two arms that are attached 232 00:13:44,460 --> 00:13:46,320 to this central circle. 233 00:13:46,320 --> 00:13:50,490 The circle is meant to represent the centromere. 234 00:13:50,490 --> 00:13:53,640 So this is the centromere. 235 00:13:53,640 --> 00:13:56,700 And you'll remember from the last lecture on Monday, 236 00:13:56,700 --> 00:14:00,150 the centromere is the piece of the chromosome 237 00:14:00,150 --> 00:14:03,930 that physically is attached to the microtubules that 238 00:14:03,930 --> 00:14:06,720 are going to pull the chromosomes to separate poles. 239 00:14:06,720 --> 00:14:09,300 OK? 240 00:14:09,300 --> 00:14:11,430 So that's called the centromere. 241 00:14:11,430 --> 00:14:13,830 And usually, it's denoted, it's like a constriction 242 00:14:13,830 --> 00:14:15,940 in the chromosome or a little circle. 243 00:14:15,940 --> 00:14:16,710 OK? 244 00:14:16,710 --> 00:14:20,820 These other parts of the chromosome are the chromosome. 245 00:14:20,820 --> 00:14:23,250 So that you have the arms of the chromosome. 246 00:14:23,250 --> 00:14:26,310 Now I'm drawing what's known as a metacentric chromosome. 247 00:14:26,310 --> 00:14:28,118 It's not important that you know that term. 248 00:14:28,118 --> 00:14:29,660 But it just means that the centromere 249 00:14:29,660 --> 00:14:31,577 is in the middle of the chromosome. 250 00:14:31,577 --> 00:14:33,910 There are other types of chromosomes with the centromere 251 00:14:33,910 --> 00:14:34,950 might be at the end. 252 00:14:34,950 --> 00:14:36,240 OK? 253 00:14:36,240 --> 00:14:39,370 So there are different types of chromosomes. 254 00:14:39,370 --> 00:14:42,270 All right, now, for all of us, we 255 00:14:42,270 --> 00:14:46,770 have cells that have different numbers of chromosomes. 256 00:14:46,770 --> 00:14:47,820 OK? 257 00:14:47,820 --> 00:14:51,180 Some of our cells are what is known as haploid. 258 00:14:54,240 --> 00:14:56,520 And what I mean by haploid is there 259 00:14:56,520 --> 00:14:58,560 is a single set of chromosomes. 260 00:15:05,200 --> 00:15:09,690 Now the cells that we have that are haploid are our gametes, 261 00:15:09,690 --> 00:15:11,770 so they're our eggs and our sperm cells. 262 00:15:11,770 --> 00:15:12,630 OK? 263 00:15:12,630 --> 00:15:14,010 So these include gametes. 264 00:15:19,720 --> 00:15:22,387 OK, but most of the cells in your body 265 00:15:22,387 --> 00:15:23,595 are what is known as diploid. 266 00:15:30,270 --> 00:15:33,840 And diploid means there's two complete sets of chromosomes. 267 00:15:45,450 --> 00:15:47,910 OK, and you get one set from one parent, 268 00:15:47,910 --> 00:15:50,380 the other set from the other parent. 269 00:15:50,380 --> 00:15:50,880 OK? 270 00:15:50,880 --> 00:15:52,560 So one set from each parent. 271 00:16:00,180 --> 00:16:05,490 OK, and I'll draw the other set like this. 272 00:16:05,490 --> 00:16:10,050 And what I'll do is I'll just shade in this one 273 00:16:10,050 --> 00:16:11,910 to denote that it's different. 274 00:16:11,910 --> 00:16:13,080 OK? 275 00:16:13,080 --> 00:16:16,440 So these two chromosomes then are 276 00:16:16,440 --> 00:16:18,910 what is known as homologous. 277 00:16:18,910 --> 00:16:22,060 They're homologous chromosomes. 278 00:16:22,060 --> 00:16:22,752 Homologous. 279 00:16:26,790 --> 00:16:36,280 OK, and what I mean by them being homologous 280 00:16:36,280 --> 00:16:39,100 is that, basically, these two chromosomes 281 00:16:39,100 --> 00:16:42,100 have the same set of genes. 282 00:16:42,100 --> 00:16:43,645 OK, so they have the same genes. 283 00:16:48,750 --> 00:16:50,420 They have the same genes. 284 00:16:50,420 --> 00:16:53,590 But they have different variants of those genes. 285 00:16:53,590 --> 00:17:03,250 OK, so different variants of these genes. 286 00:17:03,250 --> 00:17:06,760 And these variants are referred to as alleles. 287 00:17:06,760 --> 00:17:09,220 OK? 288 00:17:09,220 --> 00:17:12,310 So if you have the same gene but they differ slightly 289 00:17:12,310 --> 00:17:16,280 in their nucleic acid sequence, then 290 00:17:16,280 --> 00:17:18,790 they're distinct alleles of those genes. 291 00:17:21,530 --> 00:17:24,880 So often, the way geneticists refer 292 00:17:24,880 --> 00:17:27,400 to these different variants or alleles 293 00:17:27,400 --> 00:17:31,300 is we use a capital letter and a lower case letter. 294 00:17:31,300 --> 00:17:34,900 OK, so this chromosome over here might have 295 00:17:34,900 --> 00:17:38,190 a gene that's allele capital a. 296 00:17:38,190 --> 00:17:41,280 And then this homologous chromosome 297 00:17:41,280 --> 00:17:44,020 will have the same gene but a different allele, which 298 00:17:44,020 --> 00:17:46,820 I'll denote lowercase a. 299 00:17:46,820 --> 00:17:47,590 OK? 300 00:17:47,590 --> 00:17:51,205 So in this case, big A and little a 301 00:17:51,205 --> 00:17:54,220 are different alleles of the same gene. 302 00:17:54,220 --> 00:17:57,940 They might produce a slightly different protein, 303 00:17:57,940 --> 00:18:01,420 which would result possibly in a different phenotype. 304 00:18:01,420 --> 00:18:02,710 OK? 305 00:18:02,710 --> 00:18:05,060 So everyone understand that distinction? 306 00:18:05,060 --> 00:18:07,300 Oh, I want to make one point because this came up 307 00:18:07,300 --> 00:18:10,240 last semester and was one of those cases 308 00:18:10,240 --> 00:18:12,970 where I forgot the part about the head. 309 00:18:12,970 --> 00:18:18,280 So we often just have two alleles when we teach genetics. 310 00:18:18,280 --> 00:18:21,280 But I hope you can see that because a gene is 311 00:18:21,280 --> 00:18:26,080 a long sequence of DNA, there is a ton of different alleles 312 00:18:26,080 --> 00:18:27,880 you can have within a given gene. 313 00:18:27,880 --> 00:18:30,520 So one nucleotide difference in that gene 314 00:18:30,520 --> 00:18:32,290 would result in a different allele. 315 00:18:32,290 --> 00:18:33,070 OK? 316 00:18:33,070 --> 00:18:34,960 So we often refer to two alleles, 317 00:18:34,960 --> 00:18:38,140 but there can be more than two alleles for a given gene. 318 00:18:38,140 --> 00:18:39,400 OK? 319 00:18:39,400 --> 00:18:43,570 Does everyone see how that manifests itself? 320 00:18:43,570 --> 00:18:44,140 OK, great. 321 00:18:44,140 --> 00:18:46,870 Any questions up until now? 322 00:18:46,870 --> 00:18:48,000 Yes, Carmen? 323 00:18:48,000 --> 00:18:50,470 AUDIENCE: So when you say that there's more than one, 324 00:18:50,470 --> 00:18:54,310 more than just the two alleles, I don't have more than one 325 00:18:54,310 --> 00:18:55,270 on each chromosome. 326 00:18:55,270 --> 00:18:57,670 So they're just more than one-- 327 00:18:57,670 --> 00:18:59,300 ADAM MARTIN: In the population. 328 00:18:59,300 --> 00:19:02,740 So Carmen asked, well, can I have 329 00:19:02,740 --> 00:19:05,050 like five alleles of a gene? 330 00:19:05,050 --> 00:19:06,820 And that's a great question. 331 00:19:06,820 --> 00:19:10,630 And so thank you, Carmen, for asking that. 332 00:19:10,630 --> 00:19:14,650 What I mean is if we consider a population as a whole, right? 333 00:19:14,650 --> 00:19:17,140 You have two alleles of each gene, 334 00:19:17,140 --> 00:19:20,350 unless it's a gene that somehow duplicated. 335 00:19:20,350 --> 00:19:23,590 And so when we're considering the population, 336 00:19:23,590 --> 00:19:25,300 there can be more than-- right? 337 00:19:25,300 --> 00:19:28,750 I mean, I see we have people with-- 338 00:19:28,750 --> 00:19:30,813 hair color is not a monogenic trait. 339 00:19:30,813 --> 00:19:32,980 But we have people with black hair, with blond hair, 340 00:19:32,980 --> 00:19:34,480 with brown hair, right? 341 00:19:34,480 --> 00:19:39,100 There is more than just two possible alleles 342 00:19:39,100 --> 00:19:40,490 with possible phenotypes. 343 00:19:40,490 --> 00:19:40,990 OK? 344 00:19:43,840 --> 00:19:46,910 All right, let's go up with this. 345 00:19:46,910 --> 00:19:48,910 All right, now I want to start at the beginning. 346 00:19:52,150 --> 00:19:55,780 So most of our cells are diploid. 347 00:19:55,780 --> 00:20:00,310 And the origin of our first diploid cell 348 00:20:00,310 --> 00:20:03,360 is from the union of two gametes. 349 00:20:03,360 --> 00:20:05,200 OK? 350 00:20:05,200 --> 00:20:07,360 So I'm going to draw two gametes here. 351 00:20:07,360 --> 00:20:08,320 Each is one n. 352 00:20:11,530 --> 00:20:15,160 And I'm just going to draw one set of chromosomes for this 353 00:20:15,160 --> 00:20:16,240 here. 354 00:20:16,240 --> 00:20:21,745 So we might have a male gamete and a female gamete. 355 00:20:27,130 --> 00:20:32,950 And what I'm referring to when I say n here, 356 00:20:32,950 --> 00:20:43,150 n is basically referring to the number of chromosomes 357 00:20:43,150 --> 00:20:44,320 per haploid genome. 358 00:20:54,280 --> 00:20:56,440 So when you have one n, it means you're 359 00:20:56,440 --> 00:21:00,155 haploid because you have only one set of haploid genome. 360 00:21:02,980 --> 00:21:08,080 But early in your life, we're all the result 361 00:21:08,080 --> 00:21:11,540 of a fusion between a male and female gamete. 362 00:21:11,540 --> 00:21:14,650 And so that creates a diploid cell. 363 00:21:14,650 --> 00:21:21,100 OK, so now, this diploid zygote, so this 364 00:21:21,100 --> 00:21:25,840 is referred to as the zygote, is diploid 365 00:21:25,840 --> 00:21:29,770 and now has a set of homologous chromosomes. 366 00:21:29,770 --> 00:21:30,400 OK? 367 00:21:30,400 --> 00:21:33,670 So I'm only drawing one set of homologous chromosomes here. 368 00:21:36,880 --> 00:21:39,070 So on the board, I'm going to stick to just one, 369 00:21:39,070 --> 00:21:41,170 so I don't have to draw them all out. 370 00:21:41,170 --> 00:21:43,120 In the slides, I have three. 371 00:21:43,120 --> 00:21:44,770 OK? 372 00:21:44,770 --> 00:21:48,260 So each of these represents a chromosome. 373 00:21:48,260 --> 00:21:50,230 These are different chromosomes. 374 00:21:50,230 --> 00:21:52,690 Different chromosomes are either different color 375 00:21:52,690 --> 00:21:56,890 or have a different centromere position. 376 00:21:56,890 --> 00:21:59,770 And then these down here that are colored 377 00:21:59,770 --> 00:22:01,930 are going to be the homologous chromosomes. 378 00:22:01,930 --> 00:22:02,590 OK? 379 00:22:02,590 --> 00:22:04,150 Do you see how I'm representing this? 380 00:22:06,830 --> 00:22:12,030 OK, so once you have the zygote, right, 381 00:22:12,030 --> 00:22:16,440 so you guys are no longer one cell, right? 382 00:22:16,440 --> 00:22:19,780 You guys each are tens of trillions of cells. 383 00:22:19,780 --> 00:22:25,620 So this zygote cell had to reproduce itself, 384 00:22:25,620 --> 00:22:27,930 and your cells had to divide, so that you 385 00:22:27,930 --> 00:22:30,645 grew into an entire multicellular organism. 386 00:22:34,220 --> 00:22:36,082 I'll just quickly erase that. 387 00:22:38,940 --> 00:22:43,020 OK, so when most of your cells divide, and most of your cells 388 00:22:43,020 --> 00:22:44,640 are known as somatic cells. 389 00:22:48,870 --> 00:22:54,240 When cells of your body or your intestine and your skin, 390 00:22:54,240 --> 00:22:57,330 when they divide, they genetically replicate 391 00:22:57,330 --> 00:22:58,560 themselves. 392 00:22:58,560 --> 00:23:01,905 And they're undergoing a type of cell division known as mitosis. 393 00:23:04,980 --> 00:23:06,090 OK? 394 00:23:06,090 --> 00:23:15,330 In mitosis, it's essentially a cloning of a cell. 395 00:23:15,330 --> 00:23:18,670 Or ideally, it's the cloning of a cell. 396 00:23:18,670 --> 00:23:21,150 So you have a diploid cell. 397 00:23:21,150 --> 00:23:23,460 It has to undergo DNA replication . 398 00:23:29,980 --> 00:23:34,390 And when a chromosome undergoes DNA replication, 399 00:23:34,390 --> 00:23:38,090 it will, during mitosis look like this. 400 00:23:38,090 --> 00:23:39,250 OK? 401 00:23:39,250 --> 00:23:44,560 And these two different arms or strands, they're 402 00:23:44,560 --> 00:23:46,060 known as sister chromatids. 403 00:23:46,060 --> 00:23:46,560 OK? 404 00:23:46,560 --> 00:23:49,450 So that's just another term you should know. 405 00:23:49,450 --> 00:23:50,860 These are sister chromatids. 406 00:23:53,650 --> 00:23:59,260 OK, and the sister chromatids, if DNA replication happens 407 00:23:59,260 --> 00:24:03,310 without any errors, should be exactly the same 408 00:24:03,310 --> 00:24:05,790 as each other in terms of nucleotide sequence. 409 00:24:05,790 --> 00:24:06,290 OK? 410 00:24:09,010 --> 00:24:11,930 So after DNA replication, this cell 411 00:24:11,930 --> 00:24:15,600 will essentially have four times the amount of DNA 412 00:24:15,600 --> 00:24:21,430 as a haploid cell. 413 00:24:21,430 --> 00:24:24,800 And it will split into two cells. 414 00:24:24,800 --> 00:24:26,410 And again, they'll both be diploid. 415 00:24:26,410 --> 00:24:26,910 OK? 416 00:24:29,605 --> 00:24:30,980 And I'll just point out, if we're 417 00:24:30,980 --> 00:24:34,240 thinking about our pair of chromosomes here, 418 00:24:34,240 --> 00:24:40,130 right, this parent cell has both homologs. 419 00:24:40,130 --> 00:24:42,140 And the daughter cells, because they 420 00:24:42,140 --> 00:24:45,000 should be genetically identical, also have both homologs. 421 00:24:50,390 --> 00:24:53,570 OK, so that's an example with just one chromosome. 422 00:24:53,570 --> 00:24:58,760 I'll take you through an example with these three chromosomes 423 00:24:58,760 --> 00:24:59,530 here-- 424 00:24:59,530 --> 00:25:01,700 all six chromosomes. 425 00:25:01,700 --> 00:25:03,950 So you have-- these are homologs. 426 00:25:03,950 --> 00:25:05,030 These are homologs. 427 00:25:05,030 --> 00:25:06,620 These are homologs. 428 00:25:06,620 --> 00:25:12,760 And during mitosis, all of these chromosomes 429 00:25:12,760 --> 00:25:15,760 initially are all over the nucleus. 430 00:25:15,760 --> 00:25:19,060 But during mitosis, they will align along 431 00:25:19,060 --> 00:25:20,980 the equator of the cell and what is 432 00:25:20,980 --> 00:25:23,150 known as the metaphase plate. 433 00:25:23,150 --> 00:25:27,720 Metaphase is just a fancy term for one particular stage 434 00:25:27,720 --> 00:25:30,820 in the mitotic cycle. 435 00:25:30,820 --> 00:25:33,670 And then what will happen is the spindle 436 00:25:33,670 --> 00:25:38,410 will attach to either one side or the other side 437 00:25:38,410 --> 00:25:40,240 of these chromosomes. 438 00:25:40,240 --> 00:25:45,430 And it will physically segregate them into different cells, OK? 439 00:25:45,430 --> 00:25:50,260 And what I hope you see here is that this has six chromosomes. 440 00:25:50,260 --> 00:25:52,090 This has six chromosomes. 441 00:25:52,090 --> 00:25:54,400 And these two daughter cells are genetically 442 00:25:54,400 --> 00:25:57,850 identical to the parent cell. 443 00:25:57,850 --> 00:26:01,090 OK, so this is known as an equational division, 444 00:26:01,090 --> 00:26:04,630 because it's totally equal. 445 00:26:04,630 --> 00:26:05,500 OK? 446 00:26:05,500 --> 00:26:10,220 And again, the daughter cells are both diploid, OK? 447 00:26:10,220 --> 00:26:12,050 So that's mitosis. 448 00:26:12,050 --> 00:26:13,325 Any questions about mitosis? 449 00:26:16,610 --> 00:26:17,330 OK. 450 00:26:17,330 --> 00:26:22,630 Moving on, we're going to talk now about another type of cell. 451 00:26:22,630 --> 00:26:23,975 And these are your germ cells. 452 00:26:26,660 --> 00:26:29,840 And these germ cells undergo an alternative form 453 00:26:29,840 --> 00:26:33,860 of cell division known as meiosis, OK? 454 00:26:33,860 --> 00:26:36,080 And your germ cells-- 455 00:26:36,080 --> 00:26:38,810 germ cells produce your egg and sperm. 456 00:26:38,810 --> 00:26:45,440 And so meiosis essentially is producing gametes, such as egg 457 00:26:45,440 --> 00:26:47,292 and sperm cells, OK? 458 00:26:53,070 --> 00:26:57,580 So what's the final product going to be? 459 00:26:57,580 --> 00:27:00,695 What should be the genomic content of the final product 460 00:27:00,695 --> 00:27:01,195 of meiosis? 461 00:27:04,240 --> 00:27:06,450 It should be one end, right? 462 00:27:06,450 --> 00:27:07,140 Who said that? 463 00:27:07,140 --> 00:27:08,607 Sorry. 464 00:27:08,607 --> 00:27:09,440 Yeah, exactly right. 465 00:27:09,440 --> 00:27:10,295 What's your name? 466 00:27:10,295 --> 00:27:10,670 AUDIENCE: Jeremy. 467 00:27:10,670 --> 00:27:11,150 ADAM MARTIN: Jeremy. 468 00:27:11,150 --> 00:27:12,620 So Jeremy is exactly right. 469 00:27:12,620 --> 00:27:13,400 Right? 470 00:27:13,400 --> 00:27:17,180 The germ cells-- in order to reproduce sexually, 471 00:27:17,180 --> 00:27:19,550 they should be haploid cells, so that they 472 00:27:19,550 --> 00:27:24,320 can combine with another haploid to give rise to a diploid, OK? 473 00:27:24,320 --> 00:27:28,220 So the ultimate result that we want 474 00:27:28,220 --> 00:27:31,190 is to have cells that are one end. 475 00:27:31,190 --> 00:27:34,400 But most of our cells to start out with 476 00:27:34,400 --> 00:27:37,520 are diploid, so they're two end, OK? 477 00:27:41,660 --> 00:27:44,750 So what's special about meiosis is you're not just 478 00:27:44,750 --> 00:27:47,090 going from two end to two end, but you're 479 00:27:47,090 --> 00:27:49,610 reducing the genetic content of the cells. 480 00:27:49,610 --> 00:27:55,610 You're going from two end to a one end content, OK? 481 00:27:55,610 --> 00:27:58,580 So again, meiosis starts with DNA replication. 482 00:28:06,280 --> 00:28:12,310 But in this case, the first division, which is meiosis I, 483 00:28:12,310 --> 00:28:13,900 is not equal. 484 00:28:13,900 --> 00:28:17,200 And it actually segregates the homologs, such 485 00:28:17,200 --> 00:28:23,290 that you get one cell that has one of the homologs duplicated 486 00:28:23,290 --> 00:28:26,270 and another cell that has the other homolog duplicated. 487 00:28:31,210 --> 00:28:33,690 OK? 488 00:28:33,690 --> 00:28:34,960 And I'll show this. 489 00:28:34,960 --> 00:28:35,980 I'll show it right now. 490 00:28:40,280 --> 00:28:42,340 So this is the same cell now. 491 00:28:42,340 --> 00:28:45,160 It's undergone DNA replication. 492 00:28:45,160 --> 00:28:47,695 As you can see, each chromosome has two copies. 493 00:28:50,260 --> 00:28:52,690 But instead of all the chromosomes lining up 494 00:28:52,690 --> 00:28:55,750 in the same position of the metaphase plate, what you see 495 00:28:55,750 --> 00:29:00,850 is that homologous chromosomes pair at the metaphase plate. 496 00:29:00,850 --> 00:29:05,620 And what happens here is that the homologous chromosomes are 497 00:29:05,620 --> 00:29:06,850 separated-- 498 00:29:06,850 --> 00:29:08,350 two different cells. 499 00:29:08,350 --> 00:29:13,150 And now, you have two cells that are not genetically identical, 500 00:29:13,150 --> 00:29:14,500 OK? 501 00:29:14,500 --> 00:29:18,370 So because there is not equational 502 00:29:18,370 --> 00:29:20,890 and there's a reduction in the genetic material that's 503 00:29:20,890 --> 00:29:22,810 present in the cells, this is known 504 00:29:22,810 --> 00:29:25,930 as a reductional division, OK? 505 00:29:25,930 --> 00:29:30,720 So that's meiosis I. And that's a reductional division. 506 00:29:30,720 --> 00:29:33,040 And then-- but this is not yet haploid. 507 00:29:35,620 --> 00:29:40,960 And so-- here, I'll just stick another one in here. 508 00:29:40,960 --> 00:29:44,890 These cells then undergo another round of division, 509 00:29:44,890 --> 00:29:46,600 which is known as meiosis II. 510 00:29:50,650 --> 00:29:54,400 And during this meiosis, these sister chromatids 511 00:29:54,400 --> 00:30:00,580 are separated, such that you're left with one chromosome. 512 00:30:03,890 --> 00:30:09,240 And my drawing-- at least one chromosome per gamete, OK? 513 00:30:09,240 --> 00:30:10,890 So each of these, then, is 1n. 514 00:30:18,520 --> 00:30:19,020 OK? 515 00:30:19,020 --> 00:30:22,240 So again, you have the chromosomes. 516 00:30:22,240 --> 00:30:26,400 But this time, you have them aligned like in mitosis. 517 00:30:26,400 --> 00:30:28,140 They align. 518 00:30:28,140 --> 00:30:30,750 The sister chromatids are physically separated. 519 00:30:30,750 --> 00:30:33,630 And now, you see this cell is genetically 520 00:30:33,630 --> 00:30:35,910 identical to this cell. 521 00:30:35,910 --> 00:30:38,190 And this cell here is genetically 522 00:30:38,190 --> 00:30:39,930 identical to this cell, OK? 523 00:30:39,930 --> 00:30:41,940 So that's meiosis II. 524 00:30:41,940 --> 00:30:43,530 And that's an equational division 525 00:30:43,530 --> 00:30:46,320 much more like mitosis, OK? 526 00:30:46,320 --> 00:30:50,160 Because the product of the division of those two cells-- 527 00:30:50,160 --> 00:30:53,250 each of those is equal, OK? 528 00:30:53,250 --> 00:30:56,190 And finally, the result of meiosis II 529 00:30:56,190 --> 00:30:59,910 is that you're then left with gametes 530 00:30:59,910 --> 00:31:02,950 that have a haploid content of their genome. 531 00:31:05,880 --> 00:31:10,290 OK, I want to end lecture by doing a demonstration. 532 00:31:10,290 --> 00:31:12,090 Let's see. 533 00:31:12,090 --> 00:31:14,880 So this could either be amazing, or it 534 00:31:14,880 --> 00:31:17,650 will be a complete disaster. 535 00:31:17,650 --> 00:31:19,180 So we're totally going to do it. 536 00:31:19,180 --> 00:31:20,490 So everyone come up. 537 00:31:33,504 --> 00:31:34,310 Right here. 538 00:31:40,840 --> 00:31:41,340 Here. 539 00:31:46,170 --> 00:31:49,510 Evelyn, you can leave when you have to go. 540 00:31:49,510 --> 00:31:54,205 And we'll have a chromosome loss event. 541 00:31:54,205 --> 00:31:55,040 OK? 542 00:31:55,040 --> 00:31:56,940 It has to be a multiple of four. 543 00:31:56,940 --> 00:32:07,765 If we have extra people label, then the people can supervise. 544 00:32:07,765 --> 00:32:10,610 Go. 545 00:32:10,610 --> 00:32:11,280 Oops, sorry. 546 00:32:17,870 --> 00:32:18,460 All right. 547 00:32:18,460 --> 00:32:19,970 What do we got here? 548 00:32:19,970 --> 00:32:21,420 Here you go, Bret, Andrew. 549 00:32:24,000 --> 00:32:24,510 Sorry. 550 00:32:24,510 --> 00:32:27,468 I hope I'm not hitting anybody. 551 00:32:27,468 --> 00:32:28,860 AUDIENCE: [INAUDIBLE] 552 00:32:28,860 --> 00:32:29,902 ADAM MARTIN: What's that? 553 00:32:29,902 --> 00:32:32,340 Yeah, that's the advantage of these. 554 00:32:35,430 --> 00:32:37,700 All right. 555 00:32:37,700 --> 00:32:40,122 Here you go, Myles. 556 00:32:40,122 --> 00:32:42,744 Let's see. 557 00:32:42,744 --> 00:32:44,040 Here you go. 558 00:32:44,040 --> 00:32:46,110 Sorry. 559 00:32:46,110 --> 00:32:48,550 Someone take this. 560 00:32:48,550 --> 00:32:49,050 All right. 561 00:32:49,050 --> 00:32:49,950 What do we got here? 562 00:32:53,110 --> 00:32:54,630 Just got a little chromosome here. 563 00:32:54,630 --> 00:33:00,958 AUDIENCE: [INAUDIBLE] 564 00:33:00,958 --> 00:33:02,000 ADAM MARTIN: Oops, sorry. 565 00:33:06,210 --> 00:33:06,710 All right. 566 00:33:06,710 --> 00:33:08,810 Who doesn't have a chromosome? 567 00:33:08,810 --> 00:33:10,820 Everyone in the class has a chromosome? 568 00:33:10,820 --> 00:33:11,990 All right. 569 00:33:11,990 --> 00:33:13,580 One of you want to come in here? 570 00:33:21,670 --> 00:33:22,170 All right. 571 00:33:22,170 --> 00:33:25,680 We'll see how constrained we are in terms of space. 572 00:33:25,680 --> 00:33:28,680 I've never been this ambitious and had this many chromosomes 573 00:33:28,680 --> 00:33:32,470 before, so I'm excited to see how this works. 574 00:33:32,470 --> 00:33:35,200 So you each have a Swim Noodle. 575 00:33:35,200 --> 00:33:38,280 They're different colors, so different colors 576 00:33:38,280 --> 00:33:41,160 represent different chromosomes. 577 00:33:41,160 --> 00:33:45,040 And then you also have Swim Noodles that have tape on them. 578 00:33:45,040 --> 00:33:47,070 And these represent different alleles 579 00:33:47,070 --> 00:33:48,330 from your other chromosomes. 580 00:33:48,330 --> 00:33:53,040 So these two chromosomes would be homologs of each other, OK? 581 00:33:53,040 --> 00:33:54,210 Does that make sense? 582 00:33:54,210 --> 00:33:56,830 OK, great. 583 00:33:56,830 --> 00:33:57,330 All right. 584 00:33:57,330 --> 00:34:02,680 Now, the metaphase plate will be along the center of the room. 585 00:34:02,680 --> 00:34:06,060 So let's first reenact mitosis. 586 00:34:06,060 --> 00:34:08,940 So why don't you guys find your sister chromatid 587 00:34:08,940 --> 00:34:11,690 and then sort of align in the middle of the room here? 588 00:34:15,420 --> 00:34:17,040 Sister or brother chromatid. 589 00:34:24,192 --> 00:34:24,900 How are we doing? 590 00:34:24,900 --> 00:34:27,500 Do we have enough space there? 591 00:34:27,500 --> 00:34:28,489 It's a little packed. 592 00:34:28,489 --> 00:34:32,330 You can see how the cell-- 593 00:34:32,330 --> 00:34:34,400 can you imagine how packed it is inside a cell? 594 00:34:37,050 --> 00:34:40,190 OK, everyone found their sister chromatid. 595 00:34:40,190 --> 00:34:42,920 Normally, the sister chromatids-- they replicate 596 00:34:42,920 --> 00:34:44,100 and they get held together. 597 00:34:44,100 --> 00:34:47,580 So there's no finding of sister chromatids, but-- 598 00:34:47,580 --> 00:34:48,080 all right. 599 00:34:48,080 --> 00:34:49,040 Great. 600 00:34:49,040 --> 00:34:53,290 So segregate and we'll see how you guys did. 601 00:35:00,040 --> 00:35:00,540 All right. 602 00:35:00,540 --> 00:35:06,710 And the goal is that you guys would be genetically identical. 603 00:35:06,710 --> 00:35:08,670 So how-- OK, great. 604 00:35:08,670 --> 00:35:13,290 That looks like one short red, one short red. 605 00:35:13,290 --> 00:35:15,150 OK, that's good. 606 00:35:21,250 --> 00:35:25,320 They look genetically identical to me. 607 00:35:25,320 --> 00:35:25,820 All right. 608 00:35:25,820 --> 00:35:27,650 So that was my mitosis. 609 00:35:27,650 --> 00:35:29,230 Now, we're going to do meiosis. 610 00:35:29,230 --> 00:35:33,590 OK, why don't you guys align, like what would happen during 611 00:35:33,590 --> 00:35:38,640 meiosis I. OK, you guys can come back. 612 00:35:38,640 --> 00:35:40,635 Think about who you're going to pair with. 613 00:35:40,635 --> 00:35:42,060 [SIDE CONVERSATION] 614 00:36:10,900 --> 00:36:11,400 All right. 615 00:36:11,400 --> 00:36:13,760 So what were you looking for when you were pairing? 616 00:36:13,760 --> 00:36:16,925 Who were you looking for? 617 00:36:16,925 --> 00:36:18,437 AUDIENCE: Longest chromosome. 618 00:36:18,437 --> 00:36:20,270 ADAM MARTIN: Your longest chromosome, right? 619 00:36:20,270 --> 00:36:21,950 OK, great. 620 00:36:21,950 --> 00:36:22,450 All right. 621 00:36:22,450 --> 00:36:23,690 Why don't you guys segregate? 622 00:36:32,730 --> 00:36:36,210 All right, so that was meiosis I. Meiosis 623 00:36:36,210 --> 00:36:40,530 I looks successful to me. 624 00:36:40,530 --> 00:36:43,170 And now, we have to undergo meiosis II. 625 00:36:43,170 --> 00:36:45,470 So maybe what we could do is you guys can rotate. 626 00:36:45,470 --> 00:36:50,290 And the metaphase spindle can be sort of in this orientation. 627 00:36:50,290 --> 00:36:51,335 AUDIENCE: [INAUDIBLE] 628 00:36:51,335 --> 00:36:52,710 ADAM MARTIN: Yeah, that will-- we 629 00:36:52,710 --> 00:36:55,320 want a group over there, a group over there, a group here, 630 00:36:55,320 --> 00:36:55,960 a group here. 631 00:36:55,960 --> 00:36:57,418 And those will be our four gametes. 632 00:36:59,815 --> 00:37:01,252 [SIDE CONVERSATION] 633 00:37:05,570 --> 00:37:06,380 All right. 634 00:37:06,380 --> 00:37:08,210 You guys set? 635 00:37:08,210 --> 00:37:08,800 All right. 636 00:37:08,800 --> 00:37:10,664 Go. 637 00:37:10,664 --> 00:37:12,158 [SIDE CONVERSATION] 638 00:37:17,150 --> 00:37:18,870 OK, terrific. 639 00:37:18,870 --> 00:37:21,750 Everyone haploid? 640 00:37:21,750 --> 00:37:26,320 Looks like everyone is haploid, which is good. 641 00:37:26,320 --> 00:37:26,820 Right? 642 00:37:26,820 --> 00:37:31,740 So let's just take a minute and think about probability here. 643 00:37:31,740 --> 00:37:34,110 So what was the probability that a gamete 644 00:37:34,110 --> 00:37:39,166 would end up with this orange allele on the red chromosome? 645 00:37:39,166 --> 00:37:40,368 AUDIENCE: Half. 646 00:37:40,368 --> 00:37:41,410 ADAM MARTIN: Half, right? 647 00:37:41,410 --> 00:37:43,020 Because there are two, right? 648 00:37:43,020 --> 00:37:45,570 So these two gametes have that allele. 649 00:37:45,570 --> 00:37:49,720 These two should not, right? 650 00:37:49,720 --> 00:37:50,640 OK, great. 651 00:37:53,160 --> 00:37:55,410 And we just had a chromosome loss, 652 00:37:55,410 --> 00:37:58,220 so that gamete is in trouble. 653 00:38:02,430 --> 00:38:09,090 But maybe we could get a TA to rescue this chromosome. 654 00:38:09,090 --> 00:38:11,210 Either one of you is fine. 655 00:38:11,210 --> 00:38:13,383 There you go, David. 656 00:38:13,383 --> 00:38:14,856 [SIDE CONVERSATION] 657 00:38:21,930 --> 00:38:22,430 All right. 658 00:38:22,430 --> 00:38:23,090 That was great. 659 00:38:23,090 --> 00:38:25,670 Now, let's-- as you're doing this, 660 00:38:25,670 --> 00:38:30,020 you get a sense as to how things could get mixed up, right? 661 00:38:30,020 --> 00:38:33,560 And you think inside the cell, right? 662 00:38:33,560 --> 00:38:34,460 So I don't-- 663 00:38:34,460 --> 00:38:36,770 I've lost track of how many chromosomes. 664 00:38:36,770 --> 00:38:39,500 We have 1, 2, 3, 4, 5, 6, right? 665 00:38:39,500 --> 00:38:41,990 How many chromosomes do we have? 666 00:38:41,990 --> 00:38:42,542 AUDIENCE: 23. 667 00:38:42,542 --> 00:38:44,000 ADAM MARTIN: We are-- a haploid set 668 00:38:44,000 --> 00:38:45,588 for us is how many chromosomes? 669 00:38:45,588 --> 00:38:46,130 AUDIENCE: 23. 670 00:38:46,130 --> 00:38:46,850 ADAM MARTIN: 23. 671 00:38:46,850 --> 00:38:47,570 Exactly. 672 00:38:47,570 --> 00:38:48,410 Right? 673 00:38:48,410 --> 00:38:51,260 So it'd be even worse for a human cell 674 00:38:51,260 --> 00:38:53,300 to get this to go right. 675 00:38:53,300 --> 00:38:56,570 So why don't you guys line up in the mitosis configuration? 676 00:38:56,570 --> 00:38:59,140 And we'll consider some things that could go wrong. 677 00:39:13,260 --> 00:39:14,430 All right. 678 00:39:14,430 --> 00:39:20,640 Who here is good friends with their sister or brother 679 00:39:20,640 --> 00:39:21,290 chromatid? 680 00:39:24,480 --> 00:39:27,000 Is anyone very good friends with their sister or brother 681 00:39:27,000 --> 00:39:27,982 chromatid? 682 00:39:30,934 --> 00:39:32,402 [LAUGHTER] 683 00:39:32,902 --> 00:39:34,380 AUDIENCE: [INAUDIBLE] 684 00:39:34,380 --> 00:39:36,000 ADAM MARTIN: Yeah. 685 00:39:36,000 --> 00:39:41,040 Someone become good friends and become inseparable, OK? 686 00:39:41,040 --> 00:39:43,890 Would someone volunteer to be inseparable? 687 00:39:43,890 --> 00:39:44,430 OK, great. 688 00:39:44,430 --> 00:39:46,590 You guys are now inseparable, OK? 689 00:39:46,590 --> 00:39:47,580 Now, segregate. 690 00:39:51,500 --> 00:39:52,090 OK, great. 691 00:39:55,830 --> 00:39:57,760 Now, what happened there? 692 00:39:57,760 --> 00:39:59,580 AUDIENCE: [INAUDIBLE] 693 00:39:59,580 --> 00:40:00,830 ADAM MARTIN: What's that? 694 00:40:00,830 --> 00:40:02,372 AUDIENCE: He stole her. 695 00:40:02,372 --> 00:40:04,080 ADAM MARTIN: Yeah, that's cell stole her. 696 00:40:04,080 --> 00:40:05,160 OK. 697 00:40:05,160 --> 00:40:10,187 So now, we have two-- a duplication of that chromosome. 698 00:40:10,187 --> 00:40:12,270 What's happened over here with this daughter cell? 699 00:40:12,270 --> 00:40:13,650 AUDIENCE: It's missing a chromosome. 700 00:40:13,650 --> 00:40:15,567 ADAM MARTIN: It's missing a chromosome, right? 701 00:40:15,567 --> 00:40:16,482 AUDIENCE: Right. 702 00:40:16,482 --> 00:40:17,940 ADAM MARTIN: So these are the types 703 00:40:17,940 --> 00:40:21,300 of mistakes that can be associated with a cell becoming 704 00:40:21,300 --> 00:40:22,350 cancerous, right? 705 00:40:22,350 --> 00:40:25,530 Because let's say there was a gene 706 00:40:25,530 --> 00:40:28,410 that suppresses growth on that chromosome. 707 00:40:28,410 --> 00:40:30,990 And it wasn't on that homolog. 708 00:40:30,990 --> 00:40:35,610 Then you might result in a genetic sort of mutant or loss 709 00:40:35,610 --> 00:40:39,150 of that gene that would result in uncontrolled proliferation. 710 00:40:39,150 --> 00:40:42,120 Also, picking up the extra copies 711 00:40:42,120 --> 00:40:44,430 of genes that promote growth could 712 00:40:44,430 --> 00:40:48,090 allow that cell to have a proliferative advantage, OK? 713 00:40:48,090 --> 00:40:50,910 We're going to-- this is sort of foreshadowing what we're 714 00:40:50,910 --> 00:40:52,390 going to talk about later. 715 00:40:52,390 --> 00:40:56,820 But I just want to plant the seed now. 716 00:40:56,820 --> 00:40:57,320 OK. 717 00:40:57,320 --> 00:40:58,890 Why don't we go back and do meiosis? 718 00:41:16,182 --> 00:41:19,668 [SIDE CONVERSATION] 719 00:41:29,332 --> 00:41:30,100 OK. 720 00:41:30,100 --> 00:41:34,870 Now, anyone see any friends looking across the aisle now? 721 00:41:40,910 --> 00:41:41,410 All right. 722 00:41:41,410 --> 00:41:41,910 Great. 723 00:41:41,910 --> 00:41:43,420 You guys are now inseparable. 724 00:41:43,420 --> 00:41:49,190 Why don't you guys segregate, except the inseparable ones? 725 00:41:49,190 --> 00:41:53,155 Oh, but your sister chromatids still have to stay attached. 726 00:41:56,588 --> 00:41:57,130 There you go. 727 00:41:57,130 --> 00:41:59,060 See? 728 00:41:59,060 --> 00:42:00,940 Great. 729 00:42:00,940 --> 00:42:01,440 Right. 730 00:42:01,440 --> 00:42:03,160 So just like last time, this is known 731 00:42:03,160 --> 00:42:06,670 as a non-disjunction event where the chromosomes don't 732 00:42:06,670 --> 00:42:08,930 separate when they should, OK? 733 00:42:08,930 --> 00:42:09,430 Great. 734 00:42:09,430 --> 00:42:13,540 Now, why don't you guys do meiosis II? 735 00:42:13,540 --> 00:42:15,025 [SIDE CONVERSATION] 736 00:42:27,180 --> 00:42:27,680 All right. 737 00:42:27,680 --> 00:42:28,550 You can segregate. 738 00:42:35,850 --> 00:42:36,350 All right. 739 00:42:36,350 --> 00:42:40,040 Now, you see these two gametes over here 740 00:42:40,040 --> 00:42:43,590 are lacking an entire orange chromosome. 741 00:42:43,590 --> 00:42:47,540 And these two gametes here have picked up an additional copy 742 00:42:47,540 --> 00:42:49,970 of an orange chromosome, OK? 743 00:42:49,970 --> 00:42:52,550 So these two gametes are no longer 744 00:42:52,550 --> 00:42:57,030 haploid for the orange chromosome. 745 00:42:57,030 --> 00:42:59,690 And if one of these gametes were to fuse 746 00:42:59,690 --> 00:43:04,130 with a haploid gamete that has an orange chromosome, 747 00:43:04,130 --> 00:43:07,880 then now you have a zygote that has 748 00:43:07,880 --> 00:43:12,500 three copies of the orange chromosome, which is abnormal, 749 00:43:12,500 --> 00:43:13,280 OK? 750 00:43:13,280 --> 00:43:16,520 So if that were chromosome 21 in humans, 751 00:43:16,520 --> 00:43:20,150 that would result in something that's called trisomy 21, which 752 00:43:20,150 --> 00:43:21,830 is down syndrome, OK? 753 00:43:21,830 --> 00:43:26,330 So you see how mistakes in how chromosomes segregate 754 00:43:26,330 --> 00:43:29,000 can result in human disease. 755 00:43:29,000 --> 00:43:29,520 OK. 756 00:43:29,520 --> 00:43:31,550 Why don't we give yourselves a hand? 757 00:43:31,550 --> 00:43:32,160 Good job. 758 00:43:32,160 --> 00:43:33,582 [APPLAUSE] 759 00:43:34,530 --> 00:43:37,250 OK, you can just throw the Pool Noodles on the side. 760 00:43:37,250 --> 00:43:39,170 And I just have one slide to show you 761 00:43:39,170 --> 00:43:42,085 where we're going next. 762 00:43:42,085 --> 00:43:42,640 [INAUDIBLE] 763 00:43:42,640 --> 00:43:46,748 [SIDE CONVERSATION] 764 00:43:46,748 --> 00:43:48,040 AUDIENCE: So I have a question. 765 00:43:48,040 --> 00:43:48,630 ADAM MARTIN: Yeah? 766 00:43:48,630 --> 00:43:50,630 AUDIENCE: When the homologous chromosomes split, 767 00:43:50,630 --> 00:43:51,875 can you share alleles? 768 00:43:51,875 --> 00:43:53,843 Are there alleles preserved in this portion? 769 00:43:53,843 --> 00:43:56,010 ADAM MARTIN: You're asking if there's crossing over? 770 00:43:56,010 --> 00:43:56,550 AUDIENCE: Yeah. 771 00:43:56,550 --> 00:43:57,470 ADAM MARTIN: There is crossing over. 772 00:43:57,470 --> 00:43:58,040 Yes. 773 00:43:58,040 --> 00:44:00,940 And that will get its own entire lecture. 774 00:44:00,940 --> 00:44:02,000 Yes, good question. 775 00:44:09,290 --> 00:44:13,620 OK, so just to give you guys a preview of what's up next. 776 00:44:13,620 --> 00:44:16,020 So in the next lecture, we're going 777 00:44:16,020 --> 00:44:19,430 to talk about Mendel and Mendel's peas. 778 00:44:19,430 --> 00:44:23,090 And we'll talk about the laws of inheritance, OK? 779 00:44:23,090 --> 00:44:28,850 And realize Mendel was way before DNA 780 00:44:28,850 --> 00:44:33,110 or what our knowledge of a gene was, OK? 781 00:44:33,110 --> 00:44:37,460 Next, we'll talk about fruit flies, and Thomas Hunt Morgan, 782 00:44:37,460 --> 00:44:43,160 and seminal work that led to the chromosome model of inheritance 783 00:44:43,160 --> 00:44:46,730 and also resulted in the concepts of linkage 784 00:44:46,730 --> 00:44:49,850 and also genetic maps. 785 00:44:49,850 --> 00:44:50,990 OK, we're going to go-- 786 00:44:50,990 --> 00:44:55,010 well, just to sort of anchor yourself, the structure of DNA 787 00:44:55,010 --> 00:44:57,530 was published in 1953. 788 00:44:57,530 --> 00:45:00,380 So these seminal genetic studies up here 789 00:45:00,380 --> 00:45:03,090 were done before we knew about DNA. 790 00:45:03,090 --> 00:45:06,830 So geneticists were studying genes and their behavior 791 00:45:06,830 --> 00:45:10,940 well before we knew DNA was what was responsible. 792 00:45:10,940 --> 00:45:14,150 And then we'll talk about sequencing and the sequencing 793 00:45:14,150 --> 00:45:15,680 revolution. 794 00:45:15,680 --> 00:45:18,740 We'll talk about cloning, and molecular biology, 795 00:45:18,740 --> 00:45:21,380 and how one might go from a human disease 796 00:45:21,380 --> 00:45:24,417 to a specific gene that causes it. 797 00:45:24,417 --> 00:45:26,000 And then, finally, we'll start talking 798 00:45:26,000 --> 00:45:30,940 about entire human genome and genome sequences. 799 00:45:30,940 --> 00:45:33,900 OK, so that's just a preview of where we're going, 800 00:45:33,900 --> 00:45:36,730 so have a great weekend.