WEBVTT 00:00:16.401 --> 00:00:19.270 ADAM MARTIN: Well, first of all, nice job on the exam. 00:00:19.270 --> 00:00:22.440 We were quite pleased with how you guys did. 00:00:22.440 --> 00:00:24.630 And so from now on in the course, 00:00:24.630 --> 00:00:26.910 Professor Imperiali has been telling you 00:00:26.910 --> 00:00:32.759 about information flow, but information flow within itself, 00:00:32.759 --> 00:00:37.770 so information flow from the DNA to the proteins that 00:00:37.770 --> 00:00:43.530 are made in the cell, which determines what that cell does. 00:00:43.530 --> 00:00:46.450 And so we're going to switch directions today. 00:00:46.450 --> 00:00:49.080 And we're going to start talking about how information 00:00:49.080 --> 00:00:52.680 flows between cells-- 00:00:52.680 --> 00:00:55.740 so from a parent cell to its daughter cells. 00:00:55.740 --> 00:00:59.160 And we're also going to talk about how information flows 00:00:59.160 --> 00:01:02.280 from generation to the next. 00:01:02.280 --> 00:01:06.810 And this, of course, is the study of genetics. 00:01:12.030 --> 00:01:15.360 And what genetics is as a discipline is it 00:01:15.360 --> 00:01:22.380 is the study of genes and their inheritance. 00:01:29.060 --> 00:01:33.570 And the genes that you inherit influences what 00:01:33.570 --> 00:01:35.340 is known as your phenotype. 00:01:41.760 --> 00:01:44.550 And what phenotype is is simply the set 00:01:44.550 --> 00:01:47.490 of traits that define you. 00:01:47.490 --> 00:01:52.455 So you can think of it as a set of observable traits. 00:02:00.330 --> 00:02:03.480 And this involves your genes, as you probably know. 00:02:03.480 --> 00:02:06.900 I mean, just this morning, I was dropping my son off at school, 00:02:06.900 --> 00:02:10.770 and he was comparing how tall he was compared to his classmates. 00:02:10.770 --> 00:02:14.880 And as he went in, he was like, thanks for the genes, dad. 00:02:14.880 --> 00:02:18.180 So I expect that many of you are going 00:02:18.180 --> 00:02:21.000 to be familiar with much of what we'll discuss, 00:02:21.000 --> 00:02:23.640 but we're going to lay a real solid foundation, 00:02:23.640 --> 00:02:27.150 because it's really fundamental for understanding 00:02:27.150 --> 00:02:32.760 the rules of inheritance and how that works. 00:02:32.760 --> 00:02:35.890 So genetics is the study of genes. 00:02:35.890 --> 00:02:39.040 So what is a gene? 00:02:39.040 --> 00:02:42.640 You can think about genes in different ways. 00:02:42.640 --> 00:02:45.370 And what we've been talking about up until now, 00:02:45.370 --> 00:02:48.120 we've been talking about molecular biology and what 00:02:48.120 --> 00:02:49.925 is known as the central dogma. 00:02:56.700 --> 00:03:03.840 And the central dogma states that the source of the code 00:03:03.840 --> 00:03:05.550 is in the DNA. 00:03:05.550 --> 00:03:09.540 And there's an information flow from a piece of DNA, 00:03:09.540 --> 00:03:11.110 which is a gene. 00:03:11.110 --> 00:03:13.050 And the gene is a piece of DNA that 00:03:13.050 --> 00:03:17.790 then encodes some sort of RNA, such as a messenger RNA. 00:03:17.790 --> 00:03:21.930 And many of these RNAs can make specific proteins 00:03:21.930 --> 00:03:26.190 that do things in your cells in your body. 00:03:26.190 --> 00:03:29.820 So that's one very molecular picture of a gene. 00:03:29.820 --> 00:03:35.130 You can think of a gene as a string of nucleotides. 00:03:35.130 --> 00:03:39.540 And there might be a reading frame in those nucleotides that 00:03:39.540 --> 00:03:42.450 encodes a protein. 00:03:42.450 --> 00:03:45.900 So that's a very molecular picture of a gene. 00:03:45.900 --> 00:03:51.180 The field of genetics started well before we knew about DNA, 00:03:51.180 --> 00:03:55.950 and its importance, and what the DNA encoded 00:03:55.950 --> 00:03:57.960 RNA which encoded proteins. 00:03:57.960 --> 00:04:01.590 So the concept of a gene is much older than that. 00:04:01.590 --> 00:04:05.130 And so another way you can think of a gene 00:04:05.130 --> 00:04:08.190 is it's essentially the functional unit of heredity. 00:04:11.530 --> 00:04:16.170 So it's the functional unit of heredity. 00:04:22.160 --> 00:04:23.400 I'll bump this up. 00:04:31.210 --> 00:04:33.850 So I want to just briefly pause and kind of give you 00:04:33.850 --> 00:04:38.020 an overview of why I think genetics is so important. 00:04:38.020 --> 00:04:41.200 So what you saw up here is you saw a cell divide. 00:04:41.200 --> 00:04:43.600 And I showed you this in the last lecture-- 00:04:43.600 --> 00:04:46.780 you saw the chromosomes, which are here, 00:04:46.780 --> 00:04:48.850 how they're segregated to different daughters. 00:04:48.850 --> 00:04:52.180 And this is-- basically, you're seeing the information flow 00:04:52.180 --> 00:04:55.600 from the parent cell into the daughter herself. 00:04:55.600 --> 00:04:58.600 But we saw this, so I'm just going to skip ahead. 00:04:58.600 --> 00:05:02.020 So why is this so important? 00:05:02.020 --> 00:05:05.050 I'm going to give you a fairly grandiose view of why 00:05:05.050 --> 00:05:07.390 genetics is so important. 00:05:07.390 --> 00:05:11.020 And I'm going to say that we can make a good argument 00:05:11.020 --> 00:05:15.430 that genetics is responsible for the rise 00:05:15.430 --> 00:05:16.810 of modern civilization. 00:05:20.170 --> 00:05:26.410 Humans, as a species, began manipulating genes and genetics 00:05:26.410 --> 00:05:29.440 even before we had any understanding of what 00:05:29.440 --> 00:05:30.230 was going on. 00:05:30.230 --> 00:05:33.400 So this is more of an unconscious selection. 00:05:33.400 --> 00:05:38.560 And so 10,000 years ago, humans were hunter gatherers. 00:05:38.560 --> 00:05:41.830 They'd go out, and try to find nuts and seeds, and hunt 00:05:41.830 --> 00:05:42.370 animals. 00:05:42.370 --> 00:05:44.410 And that's how we got our food. 00:05:44.410 --> 00:05:48.190 But around 10,000 years ago was the first example 00:05:48.190 --> 00:05:51.370 of where humans, as a species, really 00:05:51.370 --> 00:05:55.960 altered the phenotype of a plant, in this case. 00:05:55.960 --> 00:06:00.740 So wild wheat and wild barley, the seeds develop in a pod. 00:06:00.740 --> 00:06:02.740 And the biology of the wild wheat 00:06:02.740 --> 00:06:05.650 is such that the pod shatters, and the seeds then 00:06:05.650 --> 00:06:08.230 spread on the ground where they can then 00:06:08.230 --> 00:06:10.630 germinate into new plants. 00:06:10.630 --> 00:06:14.410 But 10,000 years ago, humans decided 00:06:14.410 --> 00:06:18.880 that it would be more ideal if we had a form of wheat which 00:06:18.880 --> 00:06:22.300 didn't shatter, which is known as non-shattering wheat 00:06:22.300 --> 00:06:26.260 in which the seeds remain on the plant. 00:06:26.260 --> 00:06:28.930 And that allows it to be easily harvested 00:06:28.930 --> 00:06:30.970 at the end of the season. 00:06:30.970 --> 00:06:34.420 So 10,000 years ago is one of the first examples 00:06:34.420 --> 00:06:37.930 where humans really genetically altered 00:06:37.930 --> 00:06:39.430 the phenotype of a plant. 00:06:39.430 --> 00:06:42.490 And they selected for this non-shattering wheat, 00:06:42.490 --> 00:06:46.870 which then allowed for the rise of agriculture. 00:06:46.870 --> 00:06:51.480 In addition to wheat, we also-- 00:06:51.480 --> 00:06:54.790 about 4,000 years ago was the rise 00:06:54.790 --> 00:06:57.620 of domesticated fruit and nuts. 00:06:57.620 --> 00:06:58.900 So here are some almonds. 00:06:58.900 --> 00:07:02.350 If you would like an almond, feel free to have some. 00:07:02.350 --> 00:07:03.500 You guys want some almonds? 00:07:03.500 --> 00:07:04.000 No. 00:07:04.000 --> 00:07:05.750 If you have a nut allergy, don't eat them. 00:07:09.100 --> 00:07:10.060 Great. 00:07:10.060 --> 00:07:14.400 So wild almonds, when you chew them, 00:07:14.400 --> 00:07:16.120 there's an enzymatic reaction that 00:07:16.120 --> 00:07:19.840 results in cyanide forming. 00:07:19.840 --> 00:07:22.810 Rachel just stopped chewing. 00:07:22.810 --> 00:07:23.450 Don't worry. 00:07:23.450 --> 00:07:27.760 These are almonds that are harvested at Trader Joe's, so 00:07:27.760 --> 00:07:29.440 you're safe. 00:07:29.440 --> 00:07:32.920 And so the wild almonds, obviously, 00:07:32.920 --> 00:07:36.130 were not compatible for consumption. 00:07:36.130 --> 00:07:39.040 But 4,000 years ago, humans again 00:07:39.040 --> 00:07:41.710 selected for a form of the almond, which 00:07:41.710 --> 00:07:44.980 involved just a single gene, which was non-bitter 00:07:44.980 --> 00:07:50.290 and known as a sweet almond, which was also not toxic. 00:07:50.290 --> 00:07:54.760 So this doesn't just go for foods, but also for clothing. 00:07:54.760 --> 00:07:58.600 So humans have selected for cotton with long lint. 00:07:58.600 --> 00:08:03.100 And that served as a basis for clothing and sort 00:08:03.100 --> 00:08:06.010 of allowing us to have fabric. 00:08:06.010 --> 00:08:09.670 And I just want to end with a little story about the almond, 00:08:09.670 --> 00:08:12.550 which is part of the archaeological evidence 00:08:12.550 --> 00:08:15.100 for when almonds were domesticated 00:08:15.100 --> 00:08:18.280 was when King Tut's tomb was unearthed. 00:08:18.280 --> 00:08:20.800 And they found a pile of almonds next to the tomb, 00:08:20.800 --> 00:08:24.520 because the Egyptian culture, what they did 00:08:24.520 --> 00:08:28.180 is they buried the dead with food to sustain them 00:08:28.180 --> 00:08:30.160 in the afterlife. 00:08:30.160 --> 00:08:32.559 So that just gives you an idea as to how far 00:08:32.559 --> 00:08:36.280 back the importance of genetics goes. 00:08:36.280 --> 00:08:38.710 If we think about nowadays, right now 00:08:38.710 --> 00:08:43.090 you are always seeing genetics in the news. 00:08:43.090 --> 00:08:45.670 And you also have the opportunity 00:08:45.670 --> 00:08:50.530 yourself to sort of do your own genetic experiment. 00:08:50.530 --> 00:08:53.830 And so now you guys are undoubtedly 00:08:53.830 --> 00:08:56.140 aware of all these companies that 00:08:56.140 --> 00:08:58.042 want you to send them your DNA. 00:08:58.042 --> 00:08:59.500 And they also want you to send them 00:08:59.500 --> 00:09:03.160 money, such that they can give you information 00:09:03.160 --> 00:09:10.270 about your family tree and also information about your health. 00:09:10.270 --> 00:09:13.130 So this is now a big business. 00:09:13.130 --> 00:09:15.340 But if you don't understand genetics, 00:09:15.340 --> 00:09:20.000 this is not as useful as it could be. 00:09:20.000 --> 00:09:21.370 So I'm just curious. 00:09:21.370 --> 00:09:24.220 How many people here have used one of these services 00:09:24.220 --> 00:09:26.960 and had their DNA genotyped? 00:09:26.960 --> 00:09:27.950 Cool. 00:09:27.950 --> 00:09:30.390 And do you think that really changed 00:09:30.390 --> 00:09:32.640 your view of who you are? 00:09:32.640 --> 00:09:34.360 Or was it kind of, eh? 00:09:34.360 --> 00:09:36.390 AUDIENCE: We actually-- I don't know if we even 00:09:36.390 --> 00:09:37.598 looked at where we came from. 00:09:37.598 --> 00:09:39.792 We looked for genetic disease. 00:09:39.792 --> 00:09:42.000 ADAM MARTIN: So you're looking for genetic disorders. 00:09:42.000 --> 00:09:46.350 And you don't have to tell me anything about that. 00:09:46.350 --> 00:09:50.830 Yeah, so I have not done this, but my dad has done it. 00:09:50.830 --> 00:09:53.970 And he will go find his relatives 00:09:53.970 --> 00:09:55.770 and bore them with our ancestry. 00:09:59.190 --> 00:10:01.980 So this is one example of how genetics is really 00:10:01.980 --> 00:10:03.720 in play today. 00:10:03.720 --> 00:10:05.400 And not everyone knows how this works. 00:10:05.400 --> 00:10:08.550 I've had people at Starbucks in the morning come up 00:10:08.550 --> 00:10:14.130 to me with their 23andMe profile and ask me to explain stuff, 00:10:14.130 --> 00:10:16.330 because they know who I am. 00:10:16.330 --> 00:10:19.200 It's a little awkward. 00:10:19.200 --> 00:10:22.350 So we can also use genetics for forensics. 00:10:22.350 --> 00:10:25.230 And so this is kind of a-- 00:10:25.230 --> 00:10:28.500 I had a lab manager in the lab, and he told me 00:10:28.500 --> 00:10:32.370 that people were doing this in senior homes 00:10:32.370 --> 00:10:35.130 in Florida, which I thought was kind of funny. 00:10:35.130 --> 00:10:40.470 What I find hilarious about this is the mug shot of the dog. 00:10:40.470 --> 00:10:42.840 That dog looks so guilty. 00:10:42.840 --> 00:10:45.540 But you can use DNA to-- 00:10:45.540 --> 00:10:48.680 you can use DNA to genotype poop. 00:10:48.680 --> 00:10:50.580 You can genotype your neighbor's dog. 00:10:50.580 --> 00:10:53.280 You can get evidence that they're the one that's 00:10:53.280 --> 00:10:55.530 pooping on your lawn. 00:10:55.530 --> 00:10:57.930 So that's a not-so-serious example. 00:10:57.930 --> 00:11:01.740 But there are more serious examples 00:11:01.740 --> 00:11:05.310 of where DNA genotyping is really having 00:11:05.310 --> 00:11:07.200 an effect in our society. 00:11:07.200 --> 00:11:10.350 And this is something I mentioned in the intro lecture. 00:11:10.350 --> 00:11:14.580 Just this past spring, someone was 00:11:14.580 --> 00:11:18.360 suspected as being the Golden State Killer. 00:11:18.360 --> 00:11:19.710 This is a cold case. 00:11:19.710 --> 00:11:23.360 The killings happened 40 years ago, 00:11:23.360 --> 00:11:28.200 but the break came from investigators getting DNA 00:11:28.200 --> 00:11:31.740 from the suspect's relatives to implicate 00:11:31.740 --> 00:11:34.380 this person in this crime. 00:11:34.380 --> 00:11:36.480 So they had DNA from the crime. 00:11:36.480 --> 00:11:39.510 And they saw that there were matches to the DNA at the crime 00:11:39.510 --> 00:11:40.530 to certain people. 00:11:40.530 --> 00:11:42.870 And then they can reconstruct who 00:11:42.870 --> 00:11:47.400 might be the person in the right place to commit the crime. 00:11:47.400 --> 00:11:48.420 So this is-- 00:11:48.420 --> 00:11:50.340 I think this is interesting, because it also 00:11:50.340 --> 00:11:54.060 leads to all sorts of privacy issues, right? 00:11:54.060 --> 00:11:59.460 Who's going to gain access to your genotype 00:11:59.460 --> 00:12:02.460 if you submitted to these companies, right? 00:12:02.460 --> 00:12:04.490 I mean, this is probably a case where 00:12:04.490 --> 00:12:08.370 I'd argue there's probably a beneficial result in that you 00:12:08.370 --> 00:12:12.150 can actually figure out if someone's committed a crime. 00:12:12.150 --> 00:12:13.800 But there are other issues in terms 00:12:13.800 --> 00:12:15.990 of thinking about insurance companies 00:12:15.990 --> 00:12:22.800 where we might be interested in having our information not 00:12:22.800 --> 00:12:25.380 publicly available to insurance companies. 00:12:25.380 --> 00:12:28.020 And maybe this is something we can discuss later 00:12:28.020 --> 00:12:31.580 on in another lecture. 00:12:31.580 --> 00:12:34.260 For today, I want to move on and go through really 00:12:34.260 --> 00:12:36.690 the fundamentals of genetics. 00:12:36.690 --> 00:12:39.720 And what I'm going to do is I'm going to start with the answer. 00:12:39.720 --> 00:12:40.410 OK? 00:12:40.410 --> 00:12:42.780 I'm going to present to you guys today 00:12:42.780 --> 00:12:46.710 the physical model for how inheritance happens. 00:12:46.710 --> 00:12:47.700 OK? 00:12:47.700 --> 00:12:54.750 So today, we're going to go over the physical model 00:12:54.750 --> 00:12:55.860 of inheritance. 00:13:02.130 --> 00:13:05.920 And this physical model involves cell division, 00:13:05.920 --> 00:13:07.950 which you saw in the last lecture 00:13:07.950 --> 00:13:11.340 and also in my opening slide. 00:13:11.340 --> 00:13:15.060 It involves cell division and the physical segregation 00:13:15.060 --> 00:13:18.190 of the chromosomes during cell division. 00:13:18.190 --> 00:13:20.160 So also chromosome segregation. 00:13:30.800 --> 00:13:34.770 OK, so this is how I'm going to represent chromosomes. 00:13:34.770 --> 00:13:40.330 And I just want to step you through what it all means. 00:13:40.330 --> 00:13:44.460 So I have these two arms that are attached 00:13:44.460 --> 00:13:46.320 to this central circle. 00:13:46.320 --> 00:13:50.490 The circle is meant to represent the centromere. 00:13:50.490 --> 00:13:53.640 So this is the centromere. 00:13:53.640 --> 00:13:56.700 And you'll remember from the last lecture on Monday, 00:13:56.700 --> 00:14:00.150 the centromere is the piece of the chromosome 00:14:00.150 --> 00:14:03.930 that physically is attached to the microtubules that 00:14:03.930 --> 00:14:06.720 are going to pull the chromosomes to separate poles. 00:14:06.720 --> 00:14:09.300 OK? 00:14:09.300 --> 00:14:11.430 So that's called the centromere. 00:14:11.430 --> 00:14:13.830 And usually, it's denoted, it's like a constriction 00:14:13.830 --> 00:14:15.940 in the chromosome or a little circle. 00:14:15.940 --> 00:14:16.710 OK? 00:14:16.710 --> 00:14:20.820 These other parts of the chromosome are the chromosome. 00:14:20.820 --> 00:14:23.250 So that you have the arms of the chromosome. 00:14:23.250 --> 00:14:26.310 Now I'm drawing what's known as a metacentric chromosome. 00:14:26.310 --> 00:14:28.118 It's not important that you know that term. 00:14:28.118 --> 00:14:29.660 But it just means that the centromere 00:14:29.660 --> 00:14:31.577 is in the middle of the chromosome. 00:14:31.577 --> 00:14:33.910 There are other types of chromosomes with the centromere 00:14:33.910 --> 00:14:34.950 might be at the end. 00:14:34.950 --> 00:14:36.240 OK? 00:14:36.240 --> 00:14:39.370 So there are different types of chromosomes. 00:14:39.370 --> 00:14:42.270 All right, now, for all of us, we 00:14:42.270 --> 00:14:46.770 have cells that have different numbers of chromosomes. 00:14:46.770 --> 00:14:47.820 OK? 00:14:47.820 --> 00:14:51.180 Some of our cells are what is known as haploid. 00:14:54.240 --> 00:14:56.520 And what I mean by haploid is there 00:14:56.520 --> 00:14:58.560 is a single set of chromosomes. 00:15:05.200 --> 00:15:09.690 Now the cells that we have that are haploid are our gametes, 00:15:09.690 --> 00:15:11.770 so they're our eggs and our sperm cells. 00:15:11.770 --> 00:15:12.630 OK? 00:15:12.630 --> 00:15:14.010 So these include gametes. 00:15:19.720 --> 00:15:22.387 OK, but most of the cells in your body 00:15:22.387 --> 00:15:23.595 are what is known as diploid. 00:15:30.270 --> 00:15:33.840 And diploid means there's two complete sets of chromosomes. 00:15:45.450 --> 00:15:47.910 OK, and you get one set from one parent, 00:15:47.910 --> 00:15:50.380 the other set from the other parent. 00:15:50.380 --> 00:15:50.880 OK? 00:15:50.880 --> 00:15:52.560 So one set from each parent. 00:16:00.180 --> 00:16:05.490 OK, and I'll draw the other set like this. 00:16:05.490 --> 00:16:10.050 And what I'll do is I'll just shade in this one 00:16:10.050 --> 00:16:11.910 to denote that it's different. 00:16:11.910 --> 00:16:13.080 OK? 00:16:13.080 --> 00:16:16.440 So these two chromosomes then are 00:16:16.440 --> 00:16:18.910 what is known as homologous. 00:16:18.910 --> 00:16:22.060 They're homologous chromosomes. 00:16:22.060 --> 00:16:22.752 Homologous. 00:16:26.790 --> 00:16:36.280 OK, and what I mean by them being homologous 00:16:36.280 --> 00:16:39.100 is that, basically, these two chromosomes 00:16:39.100 --> 00:16:42.100 have the same set of genes. 00:16:42.100 --> 00:16:43.645 OK, so they have the same genes. 00:16:48.750 --> 00:16:50.420 They have the same genes. 00:16:50.420 --> 00:16:53.590 But they have different variants of those genes. 00:16:53.590 --> 00:17:03.250 OK, so different variants of these genes. 00:17:03.250 --> 00:17:06.760 And these variants are referred to as alleles. 00:17:06.760 --> 00:17:09.220 OK? 00:17:09.220 --> 00:17:12.310 So if you have the same gene but they differ slightly 00:17:12.310 --> 00:17:16.280 in their nucleic acid sequence, then 00:17:16.280 --> 00:17:18.790 they're distinct alleles of those genes. 00:17:21.530 --> 00:17:24.880 So often, the way geneticists refer 00:17:24.880 --> 00:17:27.400 to these different variants or alleles 00:17:27.400 --> 00:17:31.300 is we use a capital letter and a lower case letter. 00:17:31.300 --> 00:17:34.900 OK, so this chromosome over here might have 00:17:34.900 --> 00:17:38.190 a gene that's allele capital a. 00:17:38.190 --> 00:17:41.280 And then this homologous chromosome 00:17:41.280 --> 00:17:44.020 will have the same gene but a different allele, which 00:17:44.020 --> 00:17:46.820 I'll denote lowercase a. 00:17:46.820 --> 00:17:47.590 OK? 00:17:47.590 --> 00:17:51.205 So in this case, big A and little a 00:17:51.205 --> 00:17:54.220 are different alleles of the same gene. 00:17:54.220 --> 00:17:57.940 They might produce a slightly different protein, 00:17:57.940 --> 00:18:01.420 which would result possibly in a different phenotype. 00:18:01.420 --> 00:18:02.710 OK? 00:18:02.710 --> 00:18:05.060 So everyone understand that distinction? 00:18:05.060 --> 00:18:07.300 Oh, I want to make one point because this came up 00:18:07.300 --> 00:18:10.240 last semester and was one of those cases 00:18:10.240 --> 00:18:12.970 where I forgot the part about the head. 00:18:12.970 --> 00:18:18.280 So we often just have two alleles when we teach genetics. 00:18:18.280 --> 00:18:21.280 But I hope you can see that because a gene is 00:18:21.280 --> 00:18:26.080 a long sequence of DNA, there is a ton of different alleles 00:18:26.080 --> 00:18:27.880 you can have within a given gene. 00:18:27.880 --> 00:18:30.520 So one nucleotide difference in that gene 00:18:30.520 --> 00:18:32.290 would result in a different allele. 00:18:32.290 --> 00:18:33.070 OK? 00:18:33.070 --> 00:18:34.960 So we often refer to two alleles, 00:18:34.960 --> 00:18:38.140 but there can be more than two alleles for a given gene. 00:18:38.140 --> 00:18:39.400 OK? 00:18:39.400 --> 00:18:43.570 Does everyone see how that manifests itself? 00:18:43.570 --> 00:18:44.140 OK, great. 00:18:44.140 --> 00:18:46.870 Any questions up until now? 00:18:46.870 --> 00:18:48.000 Yes, Carmen? 00:18:48.000 --> 00:18:50.470 AUDIENCE: So when you say that there's more than one, 00:18:50.470 --> 00:18:54.310 more than just the two alleles, I don't have more than one 00:18:54.310 --> 00:18:55.270 on each chromosome. 00:18:55.270 --> 00:18:57.670 So they're just more than one-- 00:18:57.670 --> 00:18:59.300 ADAM MARTIN: In the population. 00:18:59.300 --> 00:19:02.740 So Carmen asked, well, can I have 00:19:02.740 --> 00:19:05.050 like five alleles of a gene? 00:19:05.050 --> 00:19:06.820 And that's a great question. 00:19:06.820 --> 00:19:10.630 And so thank you, Carmen, for asking that. 00:19:10.630 --> 00:19:14.650 What I mean is if we consider a population as a whole, right? 00:19:14.650 --> 00:19:17.140 You have two alleles of each gene, 00:19:17.140 --> 00:19:20.350 unless it's a gene that somehow duplicated. 00:19:20.350 --> 00:19:23.590 And so when we're considering the population, 00:19:23.590 --> 00:19:25.300 there can be more than-- right? 00:19:25.300 --> 00:19:28.750 I mean, I see we have people with-- 00:19:28.750 --> 00:19:30.813 hair color is not a monogenic trait. 00:19:30.813 --> 00:19:32.980 But we have people with black hair, with blond hair, 00:19:32.980 --> 00:19:34.480 with brown hair, right? 00:19:34.480 --> 00:19:39.100 There is more than just two possible alleles 00:19:39.100 --> 00:19:40.490 with possible phenotypes. 00:19:40.490 --> 00:19:40.990 OK? 00:19:43.840 --> 00:19:46.910 All right, let's go up with this. 00:19:46.910 --> 00:19:48.910 All right, now I want to start at the beginning. 00:19:52.150 --> 00:19:55.780 So most of our cells are diploid. 00:19:55.780 --> 00:20:00.310 And the origin of our first diploid cell 00:20:00.310 --> 00:20:03.360 is from the union of two gametes. 00:20:03.360 --> 00:20:05.200 OK? 00:20:05.200 --> 00:20:07.360 So I'm going to draw two gametes here. 00:20:07.360 --> 00:20:08.320 Each is one n. 00:20:11.530 --> 00:20:15.160 And I'm just going to draw one set of chromosomes for this 00:20:15.160 --> 00:20:16.240 here. 00:20:16.240 --> 00:20:21.745 So we might have a male gamete and a female gamete. 00:20:27.130 --> 00:20:32.950 And what I'm referring to when I say n here, 00:20:32.950 --> 00:20:43.150 n is basically referring to the number of chromosomes 00:20:43.150 --> 00:20:44.320 per haploid genome. 00:20:54.280 --> 00:20:56.440 So when you have one n, it means you're 00:20:56.440 --> 00:21:00.155 haploid because you have only one set of haploid genome. 00:21:02.980 --> 00:21:08.080 But early in your life, we're all the result 00:21:08.080 --> 00:21:11.540 of a fusion between a male and female gamete. 00:21:11.540 --> 00:21:14.650 And so that creates a diploid cell. 00:21:14.650 --> 00:21:21.100 OK, so now, this diploid zygote, so this 00:21:21.100 --> 00:21:25.840 is referred to as the zygote, is diploid 00:21:25.840 --> 00:21:29.770 and now has a set of homologous chromosomes. 00:21:29.770 --> 00:21:30.400 OK? 00:21:30.400 --> 00:21:33.670 So I'm only drawing one set of homologous chromosomes here. 00:21:36.880 --> 00:21:39.070 So on the board, I'm going to stick to just one, 00:21:39.070 --> 00:21:41.170 so I don't have to draw them all out. 00:21:41.170 --> 00:21:43.120 In the slides, I have three. 00:21:43.120 --> 00:21:44.770 OK? 00:21:44.770 --> 00:21:48.260 So each of these represents a chromosome. 00:21:48.260 --> 00:21:50.230 These are different chromosomes. 00:21:50.230 --> 00:21:52.690 Different chromosomes are either different color 00:21:52.690 --> 00:21:56.890 or have a different centromere position. 00:21:56.890 --> 00:21:59.770 And then these down here that are colored 00:21:59.770 --> 00:22:01.930 are going to be the homologous chromosomes. 00:22:01.930 --> 00:22:02.590 OK? 00:22:02.590 --> 00:22:04.150 Do you see how I'm representing this? 00:22:06.830 --> 00:22:12.030 OK, so once you have the zygote, right, 00:22:12.030 --> 00:22:16.440 so you guys are no longer one cell, right? 00:22:16.440 --> 00:22:19.780 You guys each are tens of trillions of cells. 00:22:19.780 --> 00:22:25.620 So this zygote cell had to reproduce itself, 00:22:25.620 --> 00:22:27.930 and your cells had to divide, so that you 00:22:27.930 --> 00:22:30.645 grew into an entire multicellular organism. 00:22:34.220 --> 00:22:36.082 I'll just quickly erase that. 00:22:38.940 --> 00:22:43.020 OK, so when most of your cells divide, and most of your cells 00:22:43.020 --> 00:22:44.640 are known as somatic cells. 00:22:48.870 --> 00:22:54.240 When cells of your body or your intestine and your skin, 00:22:54.240 --> 00:22:57.330 when they divide, they genetically replicate 00:22:57.330 --> 00:22:58.560 themselves. 00:22:58.560 --> 00:23:01.905 And they're undergoing a type of cell division known as mitosis. 00:23:04.980 --> 00:23:06.090 OK? 00:23:06.090 --> 00:23:15.330 In mitosis, it's essentially a cloning of a cell. 00:23:15.330 --> 00:23:18.670 Or ideally, it's the cloning of a cell. 00:23:18.670 --> 00:23:21.150 So you have a diploid cell. 00:23:21.150 --> 00:23:23.460 It has to undergo DNA replication . 00:23:29.980 --> 00:23:34.390 And when a chromosome undergoes DNA replication, 00:23:34.390 --> 00:23:38.090 it will, during mitosis look like this. 00:23:38.090 --> 00:23:39.250 OK? 00:23:39.250 --> 00:23:44.560 And these two different arms or strands, they're 00:23:44.560 --> 00:23:46.060 known as sister chromatids. 00:23:46.060 --> 00:23:46.560 OK? 00:23:46.560 --> 00:23:49.450 So that's just another term you should know. 00:23:49.450 --> 00:23:50.860 These are sister chromatids. 00:23:53.650 --> 00:23:59.260 OK, and the sister chromatids, if DNA replication happens 00:23:59.260 --> 00:24:03.310 without any errors, should be exactly the same 00:24:03.310 --> 00:24:05.790 as each other in terms of nucleotide sequence. 00:24:05.790 --> 00:24:06.290 OK? 00:24:09.010 --> 00:24:11.930 So after DNA replication, this cell 00:24:11.930 --> 00:24:15.600 will essentially have four times the amount of DNA 00:24:15.600 --> 00:24:21.430 as a haploid cell. 00:24:21.430 --> 00:24:24.800 And it will split into two cells. 00:24:24.800 --> 00:24:26.410 And again, they'll both be diploid. 00:24:26.410 --> 00:24:26.910 OK? 00:24:29.605 --> 00:24:30.980 And I'll just point out, if we're 00:24:30.980 --> 00:24:34.240 thinking about our pair of chromosomes here, 00:24:34.240 --> 00:24:40.130 right, this parent cell has both homologs. 00:24:40.130 --> 00:24:42.140 And the daughter cells, because they 00:24:42.140 --> 00:24:45.000 should be genetically identical, also have both homologs. 00:24:50.390 --> 00:24:53.570 OK, so that's an example with just one chromosome. 00:24:53.570 --> 00:24:58.760 I'll take you through an example with these three chromosomes 00:24:58.760 --> 00:24:59.530 here-- 00:24:59.530 --> 00:25:01.700 all six chromosomes. 00:25:01.700 --> 00:25:03.950 So you have-- these are homologs. 00:25:03.950 --> 00:25:05.030 These are homologs. 00:25:05.030 --> 00:25:06.620 These are homologs. 00:25:06.620 --> 00:25:12.760 And during mitosis, all of these chromosomes 00:25:12.760 --> 00:25:15.760 initially are all over the nucleus. 00:25:15.760 --> 00:25:19.060 But during mitosis, they will align along 00:25:19.060 --> 00:25:20.980 the equator of the cell and what is 00:25:20.980 --> 00:25:23.150 known as the metaphase plate. 00:25:23.150 --> 00:25:27.720 Metaphase is just a fancy term for one particular stage 00:25:27.720 --> 00:25:30.820 in the mitotic cycle. 00:25:30.820 --> 00:25:33.670 And then what will happen is the spindle 00:25:33.670 --> 00:25:38.410 will attach to either one side or the other side 00:25:38.410 --> 00:25:40.240 of these chromosomes. 00:25:40.240 --> 00:25:45.430 And it will physically segregate them into different cells, OK? 00:25:45.430 --> 00:25:50.260 And what I hope you see here is that this has six chromosomes. 00:25:50.260 --> 00:25:52.090 This has six chromosomes. 00:25:52.090 --> 00:25:54.400 And these two daughter cells are genetically 00:25:54.400 --> 00:25:57.850 identical to the parent cell. 00:25:57.850 --> 00:26:01.090 OK, so this is known as an equational division, 00:26:01.090 --> 00:26:04.630 because it's totally equal. 00:26:04.630 --> 00:26:05.500 OK? 00:26:05.500 --> 00:26:10.220 And again, the daughter cells are both diploid, OK? 00:26:10.220 --> 00:26:12.050 So that's mitosis. 00:26:12.050 --> 00:26:13.325 Any questions about mitosis? 00:26:16.610 --> 00:26:17.330 OK. 00:26:17.330 --> 00:26:22.630 Moving on, we're going to talk now about another type of cell. 00:26:22.630 --> 00:26:23.975 And these are your germ cells. 00:26:26.660 --> 00:26:29.840 And these germ cells undergo an alternative form 00:26:29.840 --> 00:26:33.860 of cell division known as meiosis, OK? 00:26:33.860 --> 00:26:36.080 And your germ cells-- 00:26:36.080 --> 00:26:38.810 germ cells produce your egg and sperm. 00:26:38.810 --> 00:26:45.440 And so meiosis essentially is producing gametes, such as egg 00:26:45.440 --> 00:26:47.292 and sperm cells, OK? 00:26:53.070 --> 00:26:57.580 So what's the final product going to be? 00:26:57.580 --> 00:27:00.695 What should be the genomic content of the final product 00:27:00.695 --> 00:27:01.195 of meiosis? 00:27:04.240 --> 00:27:06.450 It should be one end, right? 00:27:06.450 --> 00:27:07.140 Who said that? 00:27:07.140 --> 00:27:08.607 Sorry. 00:27:08.607 --> 00:27:09.440 Yeah, exactly right. 00:27:09.440 --> 00:27:10.295 What's your name? 00:27:10.295 --> 00:27:10.670 AUDIENCE: Jeremy. 00:27:10.670 --> 00:27:11.150 ADAM MARTIN: Jeremy. 00:27:11.150 --> 00:27:12.620 So Jeremy is exactly right. 00:27:12.620 --> 00:27:13.400 Right? 00:27:13.400 --> 00:27:17.180 The germ cells-- in order to reproduce sexually, 00:27:17.180 --> 00:27:19.550 they should be haploid cells, so that they 00:27:19.550 --> 00:27:24.320 can combine with another haploid to give rise to a diploid, OK? 00:27:24.320 --> 00:27:28.220 So the ultimate result that we want 00:27:28.220 --> 00:27:31.190 is to have cells that are one end. 00:27:31.190 --> 00:27:34.400 But most of our cells to start out with 00:27:34.400 --> 00:27:37.520 are diploid, so they're two end, OK? 00:27:41.660 --> 00:27:44.750 So what's special about meiosis is you're not just 00:27:44.750 --> 00:27:47.090 going from two end to two end, but you're 00:27:47.090 --> 00:27:49.610 reducing the genetic content of the cells. 00:27:49.610 --> 00:27:55.610 You're going from two end to a one end content, OK? 00:27:55.610 --> 00:27:58.580 So again, meiosis starts with DNA replication. 00:28:06.280 --> 00:28:12.310 But in this case, the first division, which is meiosis I, 00:28:12.310 --> 00:28:13.900 is not equal. 00:28:13.900 --> 00:28:17.200 And it actually segregates the homologs, such 00:28:17.200 --> 00:28:23.290 that you get one cell that has one of the homologs duplicated 00:28:23.290 --> 00:28:26.270 and another cell that has the other homolog duplicated. 00:28:31.210 --> 00:28:33.690 OK? 00:28:33.690 --> 00:28:34.960 And I'll show this. 00:28:34.960 --> 00:28:35.980 I'll show it right now. 00:28:40.280 --> 00:28:42.340 So this is the same cell now. 00:28:42.340 --> 00:28:45.160 It's undergone DNA replication. 00:28:45.160 --> 00:28:47.695 As you can see, each chromosome has two copies. 00:28:50.260 --> 00:28:52.690 But instead of all the chromosomes lining up 00:28:52.690 --> 00:28:55.750 in the same position of the metaphase plate, what you see 00:28:55.750 --> 00:29:00.850 is that homologous chromosomes pair at the metaphase plate. 00:29:00.850 --> 00:29:05.620 And what happens here is that the homologous chromosomes are 00:29:05.620 --> 00:29:06.850 separated-- 00:29:06.850 --> 00:29:08.350 two different cells. 00:29:08.350 --> 00:29:13.150 And now, you have two cells that are not genetically identical, 00:29:13.150 --> 00:29:14.500 OK? 00:29:14.500 --> 00:29:18.370 So because there is not equational 00:29:18.370 --> 00:29:20.890 and there's a reduction in the genetic material that's 00:29:20.890 --> 00:29:22.810 present in the cells, this is known 00:29:22.810 --> 00:29:25.930 as a reductional division, OK? 00:29:25.930 --> 00:29:30.720 So that's meiosis I. And that's a reductional division. 00:29:30.720 --> 00:29:33.040 And then-- but this is not yet haploid. 00:29:35.620 --> 00:29:40.960 And so-- here, I'll just stick another one in here. 00:29:40.960 --> 00:29:44.890 These cells then undergo another round of division, 00:29:44.890 --> 00:29:46.600 which is known as meiosis II. 00:29:50.650 --> 00:29:54.400 And during this meiosis, these sister chromatids 00:29:54.400 --> 00:30:00.580 are separated, such that you're left with one chromosome. 00:30:03.890 --> 00:30:09.240 And my drawing-- at least one chromosome per gamete, OK? 00:30:09.240 --> 00:30:10.890 So each of these, then, is 1n. 00:30:18.520 --> 00:30:19.020 OK? 00:30:19.020 --> 00:30:22.240 So again, you have the chromosomes. 00:30:22.240 --> 00:30:26.400 But this time, you have them aligned like in mitosis. 00:30:26.400 --> 00:30:28.140 They align. 00:30:28.140 --> 00:30:30.750 The sister chromatids are physically separated. 00:30:30.750 --> 00:30:33.630 And now, you see this cell is genetically 00:30:33.630 --> 00:30:35.910 identical to this cell. 00:30:35.910 --> 00:30:38.190 And this cell here is genetically 00:30:38.190 --> 00:30:39.930 identical to this cell, OK? 00:30:39.930 --> 00:30:41.940 So that's meiosis II. 00:30:41.940 --> 00:30:43.530 And that's an equational division 00:30:43.530 --> 00:30:46.320 much more like mitosis, OK? 00:30:46.320 --> 00:30:50.160 Because the product of the division of those two cells-- 00:30:50.160 --> 00:30:53.250 each of those is equal, OK? 00:30:53.250 --> 00:30:56.190 And finally, the result of meiosis II 00:30:56.190 --> 00:30:59.910 is that you're then left with gametes 00:30:59.910 --> 00:31:02.950 that have a haploid content of their genome. 00:31:05.880 --> 00:31:10.290 OK, I want to end lecture by doing a demonstration. 00:31:10.290 --> 00:31:12.090 Let's see. 00:31:12.090 --> 00:31:14.880 So this could either be amazing, or it 00:31:14.880 --> 00:31:17.650 will be a complete disaster. 00:31:17.650 --> 00:31:19.180 So we're totally going to do it. 00:31:19.180 --> 00:31:20.490 So everyone come up. 00:31:33.504 --> 00:31:34.310 Right here. 00:31:40.840 --> 00:31:41.340 Here. 00:31:46.170 --> 00:31:49.510 Evelyn, you can leave when you have to go. 00:31:49.510 --> 00:31:54.205 And we'll have a chromosome loss event. 00:31:54.205 --> 00:31:55.040 OK? 00:31:55.040 --> 00:31:56.940 It has to be a multiple of four. 00:31:56.940 --> 00:32:07.765 If we have extra people label, then the people can supervise. 00:32:07.765 --> 00:32:10.610 Go. 00:32:10.610 --> 00:32:11.280 Oops, sorry. 00:32:17.870 --> 00:32:18.460 All right. 00:32:18.460 --> 00:32:19.970 What do we got here? 00:32:19.970 --> 00:32:21.420 Here you go, Bret, Andrew. 00:32:24.000 --> 00:32:24.510 Sorry. 00:32:24.510 --> 00:32:27.468 I hope I'm not hitting anybody. 00:32:27.468 --> 00:32:28.860 AUDIENCE: [INAUDIBLE] 00:32:28.860 --> 00:32:29.902 ADAM MARTIN: What's that? 00:32:29.902 --> 00:32:32.340 Yeah, that's the advantage of these. 00:32:35.430 --> 00:32:37.700 All right. 00:32:37.700 --> 00:32:40.122 Here you go, Myles. 00:32:40.122 --> 00:32:42.744 Let's see. 00:32:42.744 --> 00:32:44.040 Here you go. 00:32:44.040 --> 00:32:46.110 Sorry. 00:32:46.110 --> 00:32:48.550 Someone take this. 00:32:48.550 --> 00:32:49.050 All right. 00:32:49.050 --> 00:32:49.950 What do we got here? 00:32:53.110 --> 00:32:54.630 Just got a little chromosome here. 00:32:54.630 --> 00:33:00.958 AUDIENCE: [INAUDIBLE] 00:33:00.958 --> 00:33:02.000 ADAM MARTIN: Oops, sorry. 00:33:06.210 --> 00:33:06.710 All right. 00:33:06.710 --> 00:33:08.810 Who doesn't have a chromosome? 00:33:08.810 --> 00:33:10.820 Everyone in the class has a chromosome? 00:33:10.820 --> 00:33:11.990 All right. 00:33:11.990 --> 00:33:13.580 One of you want to come in here? 00:33:21.670 --> 00:33:22.170 All right. 00:33:22.170 --> 00:33:25.680 We'll see how constrained we are in terms of space. 00:33:25.680 --> 00:33:28.680 I've never been this ambitious and had this many chromosomes 00:33:28.680 --> 00:33:32.470 before, so I'm excited to see how this works. 00:33:32.470 --> 00:33:35.200 So you each have a Swim Noodle. 00:33:35.200 --> 00:33:38.280 They're different colors, so different colors 00:33:38.280 --> 00:33:41.160 represent different chromosomes. 00:33:41.160 --> 00:33:45.040 And then you also have Swim Noodles that have tape on them. 00:33:45.040 --> 00:33:47.070 And these represent different alleles 00:33:47.070 --> 00:33:48.330 from your other chromosomes. 00:33:48.330 --> 00:33:53.040 So these two chromosomes would be homologs of each other, OK? 00:33:53.040 --> 00:33:54.210 Does that make sense? 00:33:54.210 --> 00:33:56.830 OK, great. 00:33:56.830 --> 00:33:57.330 All right. 00:33:57.330 --> 00:34:02.680 Now, the metaphase plate will be along the center of the room. 00:34:02.680 --> 00:34:06.060 So let's first reenact mitosis. 00:34:06.060 --> 00:34:08.940 So why don't you guys find your sister chromatid 00:34:08.940 --> 00:34:11.690 and then sort of align in the middle of the room here? 00:34:15.420 --> 00:34:17.040 Sister or brother chromatid. 00:34:24.192 --> 00:34:24.900 How are we doing? 00:34:24.900 --> 00:34:27.500 Do we have enough space there? 00:34:27.500 --> 00:34:28.489 It's a little packed. 00:34:28.489 --> 00:34:32.330 You can see how the cell-- 00:34:32.330 --> 00:34:34.400 can you imagine how packed it is inside a cell? 00:34:37.050 --> 00:34:40.190 OK, everyone found their sister chromatid. 00:34:40.190 --> 00:34:42.920 Normally, the sister chromatids-- they replicate 00:34:42.920 --> 00:34:44.100 and they get held together. 00:34:44.100 --> 00:34:47.580 So there's no finding of sister chromatids, but-- 00:34:47.580 --> 00:34:48.080 all right. 00:34:48.080 --> 00:34:49.040 Great. 00:34:49.040 --> 00:34:53.290 So segregate and we'll see how you guys did. 00:35:00.040 --> 00:35:00.540 All right. 00:35:00.540 --> 00:35:06.710 And the goal is that you guys would be genetically identical. 00:35:06.710 --> 00:35:08.670 So how-- OK, great. 00:35:08.670 --> 00:35:13.290 That looks like one short red, one short red. 00:35:13.290 --> 00:35:15.150 OK, that's good. 00:35:21.250 --> 00:35:25.320 They look genetically identical to me. 00:35:25.320 --> 00:35:25.820 All right. 00:35:25.820 --> 00:35:27.650 So that was my mitosis. 00:35:27.650 --> 00:35:29.230 Now, we're going to do meiosis. 00:35:29.230 --> 00:35:33.590 OK, why don't you guys align, like what would happen during 00:35:33.590 --> 00:35:38.640 meiosis I. OK, you guys can come back. 00:35:38.640 --> 00:35:40.635 Think about who you're going to pair with. 00:35:40.635 --> 00:35:42.060 [SIDE CONVERSATION] 00:36:10.900 --> 00:36:11.400 All right. 00:36:11.400 --> 00:36:13.760 So what were you looking for when you were pairing? 00:36:13.760 --> 00:36:16.925 Who were you looking for? 00:36:16.925 --> 00:36:18.437 AUDIENCE: Longest chromosome. 00:36:18.437 --> 00:36:20.270 ADAM MARTIN: Your longest chromosome, right? 00:36:20.270 --> 00:36:21.950 OK, great. 00:36:21.950 --> 00:36:22.450 All right. 00:36:22.450 --> 00:36:23.690 Why don't you guys segregate? 00:36:32.730 --> 00:36:36.210 All right, so that was meiosis I. Meiosis 00:36:36.210 --> 00:36:40.530 I looks successful to me. 00:36:40.530 --> 00:36:43.170 And now, we have to undergo meiosis II. 00:36:43.170 --> 00:36:45.470 So maybe what we could do is you guys can rotate. 00:36:45.470 --> 00:36:50.290 And the metaphase spindle can be sort of in this orientation. 00:36:50.290 --> 00:36:51.335 AUDIENCE: [INAUDIBLE] 00:36:51.335 --> 00:36:52.710 ADAM MARTIN: Yeah, that will-- we 00:36:52.710 --> 00:36:55.320 want a group over there, a group over there, a group here, 00:36:55.320 --> 00:36:55.960 a group here. 00:36:55.960 --> 00:36:57.418 And those will be our four gametes. 00:36:59.815 --> 00:37:01.252 [SIDE CONVERSATION] 00:37:05.570 --> 00:37:06.380 All right. 00:37:06.380 --> 00:37:08.210 You guys set? 00:37:08.210 --> 00:37:08.800 All right. 00:37:08.800 --> 00:37:10.664 Go. 00:37:10.664 --> 00:37:12.158 [SIDE CONVERSATION] 00:37:17.150 --> 00:37:18.870 OK, terrific. 00:37:18.870 --> 00:37:21.750 Everyone haploid? 00:37:21.750 --> 00:37:26.320 Looks like everyone is haploid, which is good. 00:37:26.320 --> 00:37:26.820 Right? 00:37:26.820 --> 00:37:31.740 So let's just take a minute and think about probability here. 00:37:31.740 --> 00:37:34.110 So what was the probability that a gamete 00:37:34.110 --> 00:37:39.166 would end up with this orange allele on the red chromosome? 00:37:39.166 --> 00:37:40.368 AUDIENCE: Half. 00:37:40.368 --> 00:37:41.410 ADAM MARTIN: Half, right? 00:37:41.410 --> 00:37:43.020 Because there are two, right? 00:37:43.020 --> 00:37:45.570 So these two gametes have that allele. 00:37:45.570 --> 00:37:49.720 These two should not, right? 00:37:49.720 --> 00:37:50.640 OK, great. 00:37:53.160 --> 00:37:55.410 And we just had a chromosome loss, 00:37:55.410 --> 00:37:58.220 so that gamete is in trouble. 00:38:02.430 --> 00:38:09.090 But maybe we could get a TA to rescue this chromosome. 00:38:09.090 --> 00:38:11.210 Either one of you is fine. 00:38:11.210 --> 00:38:13.383 There you go, David. 00:38:13.383 --> 00:38:14.856 [SIDE CONVERSATION] 00:38:21.930 --> 00:38:22.430 All right. 00:38:22.430 --> 00:38:23.090 That was great. 00:38:23.090 --> 00:38:25.670 Now, let's-- as you're doing this, 00:38:25.670 --> 00:38:30.020 you get a sense as to how things could get mixed up, right? 00:38:30.020 --> 00:38:33.560 And you think inside the cell, right? 00:38:33.560 --> 00:38:34.460 So I don't-- 00:38:34.460 --> 00:38:36.770 I've lost track of how many chromosomes. 00:38:36.770 --> 00:38:39.500 We have 1, 2, 3, 4, 5, 6, right? 00:38:39.500 --> 00:38:41.990 How many chromosomes do we have? 00:38:41.990 --> 00:38:42.542 AUDIENCE: 23. 00:38:42.542 --> 00:38:44.000 ADAM MARTIN: We are-- a haploid set 00:38:44.000 --> 00:38:45.588 for us is how many chromosomes? 00:38:45.588 --> 00:38:46.130 AUDIENCE: 23. 00:38:46.130 --> 00:38:46.850 ADAM MARTIN: 23. 00:38:46.850 --> 00:38:47.570 Exactly. 00:38:47.570 --> 00:38:48.410 Right? 00:38:48.410 --> 00:38:51.260 So it'd be even worse for a human cell 00:38:51.260 --> 00:38:53.300 to get this to go right. 00:38:53.300 --> 00:38:56.570 So why don't you guys line up in the mitosis configuration? 00:38:56.570 --> 00:38:59.140 And we'll consider some things that could go wrong. 00:39:13.260 --> 00:39:14.430 All right. 00:39:14.430 --> 00:39:20.640 Who here is good friends with their sister or brother 00:39:20.640 --> 00:39:21.290 chromatid? 00:39:24.480 --> 00:39:27.000 Is anyone very good friends with their sister or brother 00:39:27.000 --> 00:39:27.982 chromatid? 00:39:30.934 --> 00:39:32.402 [LAUGHTER] 00:39:32.902 --> 00:39:34.380 AUDIENCE: [INAUDIBLE] 00:39:34.380 --> 00:39:36.000 ADAM MARTIN: Yeah. 00:39:36.000 --> 00:39:41.040 Someone become good friends and become inseparable, OK? 00:39:41.040 --> 00:39:43.890 Would someone volunteer to be inseparable? 00:39:43.890 --> 00:39:44.430 OK, great. 00:39:44.430 --> 00:39:46.590 You guys are now inseparable, OK? 00:39:46.590 --> 00:39:47.580 Now, segregate. 00:39:51.500 --> 00:39:52.090 OK, great. 00:39:55.830 --> 00:39:57.760 Now, what happened there? 00:39:57.760 --> 00:39:59.580 AUDIENCE: [INAUDIBLE] 00:39:59.580 --> 00:40:00.830 ADAM MARTIN: What's that? 00:40:00.830 --> 00:40:02.372 AUDIENCE: He stole her. 00:40:02.372 --> 00:40:04.080 ADAM MARTIN: Yeah, that's cell stole her. 00:40:04.080 --> 00:40:05.160 OK. 00:40:05.160 --> 00:40:10.187 So now, we have two-- a duplication of that chromosome. 00:40:10.187 --> 00:40:12.270 What's happened over here with this daughter cell? 00:40:12.270 --> 00:40:13.650 AUDIENCE: It's missing a chromosome. 00:40:13.650 --> 00:40:15.567 ADAM MARTIN: It's missing a chromosome, right? 00:40:15.567 --> 00:40:16.482 AUDIENCE: Right. 00:40:16.482 --> 00:40:17.940 ADAM MARTIN: So these are the types 00:40:17.940 --> 00:40:21.300 of mistakes that can be associated with a cell becoming 00:40:21.300 --> 00:40:22.350 cancerous, right? 00:40:22.350 --> 00:40:25.530 Because let's say there was a gene 00:40:25.530 --> 00:40:28.410 that suppresses growth on that chromosome. 00:40:28.410 --> 00:40:30.990 And it wasn't on that homolog. 00:40:30.990 --> 00:40:35.610 Then you might result in a genetic sort of mutant or loss 00:40:35.610 --> 00:40:39.150 of that gene that would result in uncontrolled proliferation. 00:40:39.150 --> 00:40:42.120 Also, picking up the extra copies 00:40:42.120 --> 00:40:44.430 of genes that promote growth could 00:40:44.430 --> 00:40:48.090 allow that cell to have a proliferative advantage, OK? 00:40:48.090 --> 00:40:50.910 We're going to-- this is sort of foreshadowing what we're 00:40:50.910 --> 00:40:52.390 going to talk about later. 00:40:52.390 --> 00:40:56.820 But I just want to plant the seed now. 00:40:56.820 --> 00:40:57.320 OK. 00:40:57.320 --> 00:40:58.890 Why don't we go back and do meiosis? 00:41:16.182 --> 00:41:19.668 [SIDE CONVERSATION] 00:41:29.332 --> 00:41:30.100 OK. 00:41:30.100 --> 00:41:34.870 Now, anyone see any friends looking across the aisle now? 00:41:40.910 --> 00:41:41.410 All right. 00:41:41.410 --> 00:41:41.910 Great. 00:41:41.910 --> 00:41:43.420 You guys are now inseparable. 00:41:43.420 --> 00:41:49.190 Why don't you guys segregate, except the inseparable ones? 00:41:49.190 --> 00:41:53.155 Oh, but your sister chromatids still have to stay attached. 00:41:56.588 --> 00:41:57.130 There you go. 00:41:57.130 --> 00:41:59.060 See? 00:41:59.060 --> 00:42:00.940 Great. 00:42:00.940 --> 00:42:01.440 Right. 00:42:01.440 --> 00:42:03.160 So just like last time, this is known 00:42:03.160 --> 00:42:06.670 as a non-disjunction event where the chromosomes don't 00:42:06.670 --> 00:42:08.930 separate when they should, OK? 00:42:08.930 --> 00:42:09.430 Great. 00:42:09.430 --> 00:42:13.540 Now, why don't you guys do meiosis II? 00:42:13.540 --> 00:42:15.025 [SIDE CONVERSATION] 00:42:27.180 --> 00:42:27.680 All right. 00:42:27.680 --> 00:42:28.550 You can segregate. 00:42:35.850 --> 00:42:36.350 All right. 00:42:36.350 --> 00:42:40.040 Now, you see these two gametes over here 00:42:40.040 --> 00:42:43.590 are lacking an entire orange chromosome. 00:42:43.590 --> 00:42:47.540 And these two gametes here have picked up an additional copy 00:42:47.540 --> 00:42:49.970 of an orange chromosome, OK? 00:42:49.970 --> 00:42:52.550 So these two gametes are no longer 00:42:52.550 --> 00:42:57.030 haploid for the orange chromosome. 00:42:57.030 --> 00:42:59.690 And if one of these gametes were to fuse 00:42:59.690 --> 00:43:04.130 with a haploid gamete that has an orange chromosome, 00:43:04.130 --> 00:43:07.880 then now you have a zygote that has 00:43:07.880 --> 00:43:12.500 three copies of the orange chromosome, which is abnormal, 00:43:12.500 --> 00:43:13.280 OK? 00:43:13.280 --> 00:43:16.520 So if that were chromosome 21 in humans, 00:43:16.520 --> 00:43:20.150 that would result in something that's called trisomy 21, which 00:43:20.150 --> 00:43:21.830 is down syndrome, OK? 00:43:21.830 --> 00:43:26.330 So you see how mistakes in how chromosomes segregate 00:43:26.330 --> 00:43:29.000 can result in human disease. 00:43:29.000 --> 00:43:29.520 OK. 00:43:29.520 --> 00:43:31.550 Why don't we give yourselves a hand? 00:43:31.550 --> 00:43:32.160 Good job. 00:43:32.160 --> 00:43:33.582 [APPLAUSE] 00:43:34.530 --> 00:43:37.250 OK, you can just throw the Pool Noodles on the side. 00:43:37.250 --> 00:43:39.170 And I just have one slide to show you 00:43:39.170 --> 00:43:42.085 where we're going next. 00:43:42.085 --> 00:43:42.640 [INAUDIBLE] 00:43:42.640 --> 00:43:46.748 [SIDE CONVERSATION] 00:43:46.748 --> 00:43:48.040 AUDIENCE: So I have a question. 00:43:48.040 --> 00:43:48.630 ADAM MARTIN: Yeah? 00:43:48.630 --> 00:43:50.630 AUDIENCE: When the homologous chromosomes split, 00:43:50.630 --> 00:43:51.875 can you share alleles? 00:43:51.875 --> 00:43:53.843 Are there alleles preserved in this portion? 00:43:53.843 --> 00:43:56.010 ADAM MARTIN: You're asking if there's crossing over? 00:43:56.010 --> 00:43:56.550 AUDIENCE: Yeah. 00:43:56.550 --> 00:43:57.470 ADAM MARTIN: There is crossing over. 00:43:57.470 --> 00:43:58.040 Yes. 00:43:58.040 --> 00:44:00.940 And that will get its own entire lecture. 00:44:00.940 --> 00:44:02.000 Yes, good question. 00:44:09.290 --> 00:44:13.620 OK, so just to give you guys a preview of what's up next. 00:44:13.620 --> 00:44:16.020 So in the next lecture, we're going 00:44:16.020 --> 00:44:19.430 to talk about Mendel and Mendel's peas. 00:44:19.430 --> 00:44:23.090 And we'll talk about the laws of inheritance, OK? 00:44:23.090 --> 00:44:28.850 And realize Mendel was way before DNA 00:44:28.850 --> 00:44:33.110 or what our knowledge of a gene was, OK? 00:44:33.110 --> 00:44:37.460 Next, we'll talk about fruit flies, and Thomas Hunt Morgan, 00:44:37.460 --> 00:44:43.160 and seminal work that led to the chromosome model of inheritance 00:44:43.160 --> 00:44:46.730 and also resulted in the concepts of linkage 00:44:46.730 --> 00:44:49.850 and also genetic maps. 00:44:49.850 --> 00:44:50.990 OK, we're going to go-- 00:44:50.990 --> 00:44:55.010 well, just to sort of anchor yourself, the structure of DNA 00:44:55.010 --> 00:44:57.530 was published in 1953. 00:44:57.530 --> 00:45:00.380 So these seminal genetic studies up here 00:45:00.380 --> 00:45:03.090 were done before we knew about DNA. 00:45:03.090 --> 00:45:06.830 So geneticists were studying genes and their behavior 00:45:06.830 --> 00:45:10.940 well before we knew DNA was what was responsible. 00:45:10.940 --> 00:45:14.150 And then we'll talk about sequencing and the sequencing 00:45:14.150 --> 00:45:15.680 revolution. 00:45:15.680 --> 00:45:18.740 We'll talk about cloning, and molecular biology, 00:45:18.740 --> 00:45:21.380 and how one might go from a human disease 00:45:21.380 --> 00:45:24.417 to a specific gene that causes it. 00:45:24.417 --> 00:45:26.000 And then, finally, we'll start talking 00:45:26.000 --> 00:45:30.940 about entire human genome and genome sequences. 00:45:30.940 --> 00:45:33.900 OK, so that's just a preview of where we're going, 00:45:33.900 --> 00:45:36.730 so have a great weekend.