1 00:00:06,253 --> 00:00:10,560 PROFESSOR: Mendel's second law-- 2 00:00:13,430 --> 00:00:18,290 this thing over here about a three to one ratio about a 3 00:00:18,290 --> 00:00:24,000 single trait being controlled by a pair of alleles, and 4 00:00:24,000 --> 00:00:29,350 those alleles being distributed independently of 5 00:00:29,350 --> 00:00:31,630 each other to the offspring, the stuff you always learned 6 00:00:31,630 --> 00:00:32,420 about Mendel-- 7 00:00:32,420 --> 00:00:35,580 that's often referred to as Mendel's first law. 8 00:00:35,580 --> 00:00:38,530 Mendel, by the way, didn't call it Mendel's first law. 9 00:00:38,530 --> 00:00:40,770 It's considered-- 10 00:00:40,770 --> 00:00:42,400 you don't write that in your own papers or something like 11 00:00:42,400 --> 00:00:43,680 that, right? 12 00:00:43,680 --> 00:00:47,760 So Mendel did actually observed some other things 13 00:00:47,760 --> 00:00:56,500 beyond this independent segregation of the alleles for 14 00:00:56,500 --> 00:00:58,510 a single trait. 15 00:00:58,510 --> 00:01:03,180 Mendel began to cross his peas together and try to make 16 00:01:03,180 --> 00:01:04,830 combinations. 17 00:01:04,830 --> 00:01:06,020 He had rounds and wrinkles. 18 00:01:06,020 --> 00:01:09,250 He had greens and yellows, talls and shorts. 19 00:01:09,250 --> 00:01:11,100 He started making combinations. 20 00:01:11,100 --> 00:01:14,630 How about a plant that was wrinkled and yellow? 21 00:01:14,630 --> 00:01:15,910 Green was the normal color. 22 00:01:15,910 --> 00:01:17,620 Round was the normal shape. 23 00:01:17,620 --> 00:01:19,020 But he had yellows. 24 00:01:19,020 --> 00:01:19,950 He had wrinkleds. 25 00:01:19,950 --> 00:01:21,760 How about making a combination? 26 00:01:21,760 --> 00:01:27,300 So he begin to make plants that bred true for different 27 00:01:27,300 --> 00:01:30,020 pairs of phenotypes. 28 00:01:30,020 --> 00:01:35,430 So for example, he had a pure breeding line here that was 29 00:01:35,430 --> 00:01:39,890 both round and green. 30 00:01:39,890 --> 00:01:42,300 That was the stuff he could pick up at the market. 31 00:01:42,300 --> 00:01:47,330 But he made a line here that was both wrinkled and yellow. 32 00:01:50,930 --> 00:01:55,840 What is the genotype of this round, green strain? 33 00:01:55,840 --> 00:01:57,500 At the round gene-- 34 00:01:57,500 --> 00:02:01,430 the gene for roundness- what is its genotype? 35 00:02:01,430 --> 00:02:04,030 Big R, big R. It's a pure breeding strain. 36 00:02:04,030 --> 00:02:05,970 It was homozygous-- 37 00:02:05,970 --> 00:02:08,340 we're just testing our words here-- homozygous 38 00:02:08,340 --> 00:02:09,600 for the big R allele. 39 00:02:12,470 --> 00:02:15,020 Green is controlled by a different gene. 40 00:02:15,020 --> 00:02:19,140 It has an allele big G. It's pure breeding for this. 41 00:02:19,140 --> 00:02:22,730 And we call it big G, big G. 42 00:02:22,730 --> 00:02:26,250 Convention, when we use capital letters, it tends to 43 00:02:26,250 --> 00:02:31,570 mean that the associated phenotype is dominant. 44 00:02:31,570 --> 00:02:32,520 OK? 45 00:02:32,520 --> 00:02:34,660 It'll make you think that the allele is dominant, but it's 46 00:02:34,660 --> 00:02:36,740 the associated phenotype that's dominant. 47 00:02:36,740 --> 00:02:38,360 Now, wrinkled-- what was wrinkled? 48 00:02:38,360 --> 00:02:42,180 Wrinkled was a homozygous wrinkled-- little r, little r. 49 00:02:42,180 --> 00:02:47,650 And what was the genotype at the yellow locus? 50 00:02:47,650 --> 00:02:50,990 Little g, a little g is how we'll denote it. 51 00:02:50,990 --> 00:02:53,670 Geneticists use four or five different kinds of notations. 52 00:02:53,670 --> 00:02:56,250 We're going to use this notation today of big R's and 53 00:02:56,250 --> 00:02:57,500 little r's and little g's. 54 00:02:57,500 --> 00:03:00,280 But you'll get used to other kinds of genetic notations. 55 00:03:00,280 --> 00:03:03,690 So when we cross these guys together, this F0 generation 56 00:03:03,690 --> 00:03:06,870 here of these two pure breeding parental strains, we 57 00:03:06,870 --> 00:03:08,940 get an F1 generation. 58 00:03:08,940 --> 00:03:10,440 The F1 generation-- 59 00:03:10,440 --> 00:03:12,550 what is it phenotypically? 60 00:03:12,550 --> 00:03:15,040 What did it look like? 61 00:03:15,040 --> 00:03:18,650 Round and green, yep-- round and green. 62 00:03:18,650 --> 00:03:19,900 What was in genotypically? 63 00:03:22,510 --> 00:03:26,460 Big R, little R, big G, little g. 64 00:03:30,230 --> 00:03:33,290 Now we could self these plants. 65 00:03:33,290 --> 00:03:35,353 And our head would hurt with the nine to three to 66 00:03:35,353 --> 00:03:36,560 three to one ratio. 67 00:03:36,560 --> 00:03:41,710 So instead, why don't we cross these plants back to the 68 00:03:41,710 --> 00:03:47,690 wrinkled, yellow strain to make our life easier? 69 00:03:47,690 --> 00:03:52,070 Little r, little r, little g, little g-- 70 00:03:52,070 --> 00:03:56,380 and when we cross that back, what is the segregation that's 71 00:03:56,380 --> 00:03:57,880 going to happen? 72 00:03:57,880 --> 00:04:02,710 Well, what are the possible gametes that could emerge from 73 00:04:02,710 --> 00:04:03,960 this parent? 74 00:04:05,860 --> 00:04:10,410 We could get a big R and a big G. We could get a big R 75 00:04:10,410 --> 00:04:12,130 and a little g. 76 00:04:12,130 --> 00:04:16,269 We could get a little r and a big G. We could get a little r 77 00:04:16,269 --> 00:04:17,180 and a little g. 78 00:04:17,180 --> 00:04:19,029 Those are the four possibilities that could be 79 00:04:19,029 --> 00:04:21,029 contributed by this parent. 80 00:04:21,029 --> 00:04:24,640 What could be contributed by this parent? 81 00:04:24,640 --> 00:04:26,420 Little r and little g-- that's it, right? 82 00:04:26,420 --> 00:04:27,960 No other options. 83 00:04:27,960 --> 00:04:30,650 So that's what our little Punnett square looks like here 84 00:04:30,650 --> 00:04:31,850 of our options-- 85 00:04:31,850 --> 00:04:36,640 parent number one, parent number two. 86 00:04:40,280 --> 00:04:41,460 What will this be? 87 00:04:41,460 --> 00:04:45,650 This will be big R, big G over little r, little g, big R, 88 00:04:45,650 --> 00:04:49,780 little g over little r little g, little r, big G over little 89 00:04:49,780 --> 00:04:53,440 r little g, little r little g over little r little g. 90 00:04:53,440 --> 00:04:57,840 In other words, this will be round and green. 91 00:04:57,840 --> 00:05:00,345 This'll be round and yellow. 92 00:05:03,140 --> 00:05:08,020 This'll be wrinkled and green. 93 00:05:08,020 --> 00:05:09,430 And this'll be wrinkled and yellow. 94 00:05:12,620 --> 00:05:14,495 And what will be the ratio of these? 95 00:05:17,670 --> 00:05:23,130 One to one to one to one, provided that those gametes 96 00:05:23,130 --> 00:05:26,230 were all equally frequent, provided that that parental 97 00:05:26,230 --> 00:05:29,750 plant made each of those four types in equal proportions. 98 00:05:29,750 --> 00:05:34,780 That one to one to one ratio in the gametes will 99 00:05:34,780 --> 00:05:39,210 necessarily translate into a one to one to one ratio in the 100 00:05:39,210 --> 00:05:43,890 phenotypes observed in the next generation. 101 00:05:43,890 --> 00:05:46,570 When we cross back-- not by selfing-- 102 00:05:46,570 --> 00:05:50,110 but when we cross back to the parent that has the recessive 103 00:05:50,110 --> 00:05:52,240 phenotypes, we'll often call this a 104 00:05:52,240 --> 00:05:55,175 backcross or a test cross. 105 00:06:02,910 --> 00:06:06,210 If I haven't done a backcross or a test cross where I 106 00:06:06,210 --> 00:06:09,530 crossed back to the wrinkled, yellow parent, I would instead 107 00:06:09,530 --> 00:06:14,110 have had to make a square here that had 16 boxes in it, and I 108 00:06:14,110 --> 00:06:17,170 would have had to add up to 16 boxes to figure out how many 109 00:06:17,170 --> 00:06:18,470 were round and green-- 110 00:06:18,470 --> 00:06:19,900 nine out of the 16. 111 00:06:19,900 --> 00:06:21,660 How many were round and yellow? 112 00:06:21,660 --> 00:06:22,710 Three out of the 16. 113 00:06:22,710 --> 00:06:24,350 How many were wrinkled and green? 114 00:06:24,350 --> 00:06:25,590 Three out of the 16. 115 00:06:25,590 --> 00:06:27,230 And how many were wrinkled and yellow? 116 00:06:27,230 --> 00:06:28,730 One out of the 16. 117 00:06:28,730 --> 00:06:31,650 But for the purposes of using the white board up here, I did 118 00:06:31,650 --> 00:06:33,710 the test cross or the backcross, 119 00:06:33,710 --> 00:06:34,970 because it's simpler. 120 00:06:34,970 --> 00:06:38,600 But you can also do the four by four matrix and figure out 121 00:06:38,600 --> 00:06:39,850 what it looks like. 122 00:06:41,970 --> 00:06:42,650 That was news. 123 00:06:42,650 --> 00:06:43,890 It didn't have to be that way, right? 124 00:06:43,890 --> 00:06:45,560 Maybe it was something else. 125 00:06:45,560 --> 00:06:46,400 This is pretty cool. 126 00:06:46,400 --> 00:06:49,840 What it tells you is not just is it the case that here the 127 00:06:49,840 --> 00:06:52,370 alleles segregate independently. 128 00:06:52,370 --> 00:06:54,960 It's a random coin flip which one you get. 129 00:06:54,960 --> 00:06:58,040 It tells you no correlation between the two traits. 130 00:06:58,040 --> 00:06:59,370 They're independent. 131 00:06:59,370 --> 00:07:03,430 This is called independent assortment. 132 00:07:03,430 --> 00:07:07,175 Mendel's second law is the law of independent assortment. 133 00:07:15,250 --> 00:07:16,500 All right. 134 00:07:20,190 --> 00:07:23,280 So Mendel publishes the paper. 135 00:07:23,280 --> 00:07:27,370 1865, it comes out. 136 00:07:27,370 --> 00:07:30,180 Here's a copy of Mendel's paper. 137 00:07:30,180 --> 00:07:32,980 It's translated into English from the original German. 138 00:07:32,980 --> 00:07:35,370 So I got Mendel's paper here. 139 00:07:35,370 --> 00:07:36,710 There's no Punnett squares. 140 00:07:36,710 --> 00:07:37,710 It's kind of messy notation. 141 00:07:37,710 --> 00:07:38,500 Look at that. 142 00:07:38,500 --> 00:07:39,970 Look at all that-- 143 00:07:39,970 --> 00:07:41,280 big A, little b. 144 00:07:41,280 --> 00:07:43,570 He's got A's, B's, C's. 145 00:07:43,570 --> 00:07:46,950 He's got three factor crosses running around in here. 146 00:07:46,950 --> 00:07:48,230 Mendel really goes to town. 147 00:07:48,230 --> 00:07:50,440 It's a beautiful paper here. 148 00:07:50,440 --> 00:07:51,670 But it just goes on and on. 149 00:07:51,670 --> 00:07:53,460 It's incredibly hard to read. 150 00:07:53,460 --> 00:07:56,512 Look at this. 151 00:07:56,512 --> 00:07:58,580 It takes a lot to read this thing. 152 00:07:58,580 --> 00:07:59,680 But in a way, it's simple. 153 00:07:59,680 --> 00:08:02,380 It's nothing so sophisticated. 154 00:08:02,380 --> 00:08:02,900 Oh yeah, here. 155 00:08:02,900 --> 00:08:06,030 Look at this-- long, green, inflated, constricted-- 156 00:08:06,030 --> 00:08:07,430 all this kind of stuff. 157 00:08:07,430 --> 00:08:08,400 It's pretty cool. 158 00:08:08,400 --> 00:08:08,960 You should look it up. 159 00:08:08,960 --> 00:08:09,440 It's online. 160 00:08:09,440 --> 00:08:10,880 You can find Mendel's paper. 161 00:08:10,880 --> 00:08:12,130 What happens to Mendel's paper? 162 00:08:16,120 --> 00:08:16,720 Nobody reads it. 163 00:08:16,720 --> 00:08:18,135 It sinks like a stone. 164 00:08:18,135 --> 00:08:21,215 It's this cool paper and nobody reads it. 165 00:08:21,215 --> 00:08:23,870 Nobody reads it for a lot of reasons. 166 00:08:23,870 --> 00:08:26,860 Scientific communication wasn't so big in those days. 167 00:08:26,860 --> 00:08:29,740 Oh, well. 168 00:08:29,740 --> 00:08:32,630 Mendel also ends up getting promoted to become the abbot 169 00:08:32,630 --> 00:08:34,460 of the monastery, and that's pretty much the end of his 170 00:08:34,460 --> 00:08:36,400 scientific career, in my opinion. 171 00:08:36,400 --> 00:08:39,020 He got too many administrative duties, doesn't do more 172 00:08:39,020 --> 00:08:40,260 science there. 173 00:08:40,260 --> 00:08:41,770 Also, he has some poor choices. 174 00:08:41,770 --> 00:08:44,320 The next plant he works on is hawk weed. 175 00:08:44,320 --> 00:08:46,870 Hawk weed turns out to have really weird genetics that 176 00:08:46,870 --> 00:08:48,570 totally leads him astray. 177 00:08:48,570 --> 00:08:50,090 Basically, this is the one important 178 00:08:50,090 --> 00:08:51,660 paper Mendel ever publishes. 179 00:08:51,660 --> 00:08:53,890 It's an incredibly important paper. 180 00:08:53,890 --> 00:08:56,060 It's so important because it contains the clue to what 181 00:08:56,060 --> 00:08:58,490 Darwin, living at exactly the same time, wished he 182 00:08:58,490 --> 00:09:01,280 understood, which is what the basis of genetic variation is. 183 00:09:01,280 --> 00:09:05,270 Wouldn't it be great if Darwin had read Mendel's paper? 184 00:09:05,270 --> 00:09:08,390 Darwin actually owned a copy of Mendel's paper. 185 00:09:08,390 --> 00:09:09,960 He received a copy of Mendel's paper. 186 00:09:09,960 --> 00:09:14,030 In those days, the way they printed books, there were 187 00:09:14,030 --> 00:09:16,950 folded pages and you had to slit the page to read it. 188 00:09:16,950 --> 00:09:20,650 Darwin never slit the pages of the copy of Mendel's paper. 189 00:09:20,650 --> 00:09:24,570 So we know he's never read Mendel's paper, but he has one 190 00:09:24,570 --> 00:09:25,810 in his library. 191 00:09:25,810 --> 00:09:26,810 He had Mendel's paper. 192 00:09:26,810 --> 00:09:28,920 He had the answers sitting there on the shelf, 193 00:09:28,920 --> 00:09:30,650 but never read it. 194 00:09:30,650 --> 00:09:32,970 The stuff sinks like a stone. 195 00:09:32,970 --> 00:09:35,390 Nobody really pays much attention to it. 196 00:09:35,390 --> 00:09:38,398 And Mendel goes on, dies that's it. 197 00:09:38,398 --> 00:09:40,490 [LAUGHTER] 198 00:09:40,490 --> 00:09:48,660 PROFESSOR: Until the end of the 1800s, right at the 199 00:09:48,660 --> 00:09:52,436 beginning of the 20th century, along comes cytology-- 200 00:09:57,430 --> 00:10:01,030 looking at cells in the microscope. 201 00:10:01,030 --> 00:10:08,910 Microscopes began to get good in the late 1800s. 202 00:10:08,910 --> 00:10:12,720 And cytologists began to see in their microscope that when 203 00:10:12,720 --> 00:10:20,720 cells divided, these funny structures began to appear-- 204 00:10:20,720 --> 00:10:23,360 these long, thread-like things. 205 00:10:23,360 --> 00:10:25,420 And the German chemical industry being developed at 206 00:10:25,420 --> 00:10:28,080 that time had invented all sorts of dyes. 207 00:10:28,080 --> 00:10:30,760 And cytologists began experimenting putting dyes on 208 00:10:30,760 --> 00:10:31,840 these cells. 209 00:10:31,840 --> 00:10:34,960 And the dyes let them see really clearly these funny 210 00:10:34,960 --> 00:10:38,400 things that were condensing out when cells divided. 211 00:10:38,400 --> 00:10:41,600 And they had no clue what these funny things were other 212 00:10:41,600 --> 00:10:43,390 than that they took up dyes. 213 00:10:43,390 --> 00:10:46,130 And so in the absence of any clue what were, they called 214 00:10:46,130 --> 00:10:53,770 them chromosomes, meaning colored things. 215 00:10:53,770 --> 00:10:56,600 That is what chromosome means. 216 00:10:56,600 --> 00:11:05,150 They called them colored thing Chromos colored bodies, 217 00:11:05,150 --> 00:11:06,050 colored things. 218 00:11:06,050 --> 00:11:07,300 That's all they knew. 219 00:11:09,900 --> 00:11:12,980 And they observed that these chromosomes, these colored 220 00:11:12,980 --> 00:11:16,090 things, did really interesting choreography. 221 00:11:16,090 --> 00:11:21,280 When cells divided, when they underwent mitosis, what would 222 00:11:21,280 --> 00:11:26,220 happen is that the chromosomes would line 223 00:11:26,220 --> 00:11:29,670 up along the midline. 224 00:11:29,670 --> 00:11:32,900 And they would have, at that point, these funny X-like 225 00:11:32,900 --> 00:11:34,150 structures. 226 00:11:40,050 --> 00:11:42,680 And I'll draw four of these chromosomes 227 00:11:42,680 --> 00:11:44,160 lining up like this. 228 00:11:44,160 --> 00:11:45,725 And what would happen during mitosis? 229 00:11:49,170 --> 00:11:54,280 The cell would divide, and each of the two cells would 230 00:11:54,280 --> 00:12:04,320 get one half of the X. So if you started with four of these 231 00:12:04,320 --> 00:12:07,610 X's, you ended up with four like this. 232 00:12:07,610 --> 00:12:09,870 There you go. 233 00:12:09,870 --> 00:12:15,055 That was the chromosome being somehow tugged apart. 234 00:12:15,055 --> 00:12:17,610 Now, anything that gets tugged apart when a cell divides-- 235 00:12:17,610 --> 00:12:18,680 that's kind of interesting. 236 00:12:18,680 --> 00:12:20,870 Then those chromosomes would disappear. 237 00:12:20,870 --> 00:12:23,440 You couldn't see them again for a while until the cell was 238 00:12:23,440 --> 00:12:24,760 ready to divide again. 239 00:12:24,760 --> 00:12:27,380 And when the cell is ready to divide again, darned if those 240 00:12:27,380 --> 00:12:29,480 single lines hadn't turned into X's. 241 00:12:29,480 --> 00:12:31,960 Somehow the cell had turned the single lines into these 242 00:12:31,960 --> 00:12:33,960 two pieces, these X's, and they were 243 00:12:33,960 --> 00:12:35,530 ready to divide again. 244 00:12:35,530 --> 00:12:37,360 And that was mitosis-- 245 00:12:37,360 --> 00:12:39,700 the process of ordinary cellular division. 246 00:12:44,110 --> 00:12:47,810 But there was another process. 247 00:12:47,810 --> 00:12:49,893 Folks observed meiosis. 248 00:12:54,080 --> 00:12:58,330 That's what happens when you make gametes. 249 00:12:58,330 --> 00:13:01,750 So when gametes get made, the 250 00:13:01,750 --> 00:13:05,390 choreography was a bit different. 251 00:13:05,390 --> 00:13:12,010 Instead of all the chromosomes lining up on the midline as 252 00:13:12,010 --> 00:13:16,470 individuals, they lined up as pairs. 253 00:13:16,470 --> 00:13:17,720 They line up as pairs. 254 00:13:21,980 --> 00:13:33,180 When the cell divides, you end up with now only two 255 00:13:33,180 --> 00:13:36,475 X's, not four X's. 256 00:13:39,990 --> 00:13:44,275 Then what happens is those cells divide again. 257 00:13:51,120 --> 00:13:54,480 And you end up with those straight lines-- 258 00:13:57,450 --> 00:13:59,220 but not four of them, only two of them. 259 00:14:03,400 --> 00:14:10,190 The first step gets called meiosis number one-- 260 00:14:10,190 --> 00:14:18,510 meiosis I. The second is called meiosis II. 261 00:14:18,510 --> 00:14:21,710 The second step looks just like mitosis, doesn't it? 262 00:14:21,710 --> 00:14:23,810 Chromosomes are lined up along the midline. 263 00:14:23,810 --> 00:14:24,550 They separate it. 264 00:14:24,550 --> 00:14:27,010 It just looks like mitosis, ordinary cell division. 265 00:14:27,010 --> 00:14:29,300 But that first step is special. 266 00:14:29,300 --> 00:14:33,250 That first step says, somehow, the chromosomes come in pairs, 267 00:14:33,250 --> 00:14:36,720 and the cell picks one from each pair and gives to its 268 00:14:36,720 --> 00:14:38,720 gametes-- its sperm or its egg-- 269 00:14:38,720 --> 00:14:42,270 one from each pair. 270 00:14:42,270 --> 00:14:44,900 And what do you think happens on fertilization? 271 00:14:44,900 --> 00:14:48,510 Well, you had one from each pair, one from each pair, it 272 00:14:48,510 --> 00:14:51,560 comes together and it restores a pair now. 273 00:14:54,200 --> 00:14:56,070 And you know what folks said? 274 00:14:56,070 --> 00:14:59,540 They said this sounds just like what that dead monk was 275 00:14:59,540 --> 00:15:02,480 talking about. 276 00:15:02,480 --> 00:15:04,980 Pairs, particles of inheritance-- 277 00:15:04,980 --> 00:15:08,560 particles that come in pairs and you give to your gametes 278 00:15:08,560 --> 00:15:11,170 one of the two pairs. 279 00:15:11,170 --> 00:15:15,440 These colored things must be the basis of inheritance or 280 00:15:15,440 --> 00:15:16,690 genes or something. 281 00:15:18,910 --> 00:15:23,630 Wow, because it fits Mendel's model beautifully. 282 00:15:23,630 --> 00:15:25,090 It explains the first law. 283 00:15:30,680 --> 00:15:33,281 What about the second law? 284 00:15:33,281 --> 00:15:36,220 What about Mendel's second law? 285 00:15:36,220 --> 00:15:42,240 How could it explain the big R and the big G being inherited 286 00:15:42,240 --> 00:15:45,340 independently of each other with no correlation? 287 00:15:45,340 --> 00:15:48,780 What would that have to mean? 288 00:15:48,780 --> 00:15:51,170 They're on different chromosomes. 289 00:15:51,170 --> 00:15:53,710 The genes are on different chromosomes. 290 00:15:53,710 --> 00:15:57,130 Because if big R is on one chromosome and big G is on the 291 00:15:57,130 --> 00:16:02,230 other chromosome, then it's a coin flip whether or not the 292 00:16:02,230 --> 00:16:05,830 big R might be here and a little r might be there or the 293 00:16:05,830 --> 00:16:09,000 big G might be there or maybe it's over there. 294 00:16:09,000 --> 00:16:11,290 It's a random draw which way it's going to go. 295 00:16:11,290 --> 00:16:14,140 So it perfectly explains Mendel's second law. 296 00:16:17,370 --> 00:16:18,620 Unless-- 297 00:16:21,070 --> 00:16:23,400 what happens if big R and big G are on the same chromosome? 298 00:16:26,430 --> 00:16:28,830 Then they're going to go together. 299 00:16:28,830 --> 00:16:31,580 I'm not going to have independent assortment. 300 00:16:31,580 --> 00:16:35,620 I may have totally dependent correlated assortment. 301 00:16:35,620 --> 00:16:37,780 If big R and big G are on the same chromosome, they're going 302 00:16:37,780 --> 00:16:38,530 to be inherited together. 303 00:16:38,530 --> 00:16:40,960 Mendel's second law is going to be wrong. 304 00:16:40,960 --> 00:16:45,020 So why did Mendel find big R and big G going together? 305 00:16:45,020 --> 00:16:46,910 Maybe was lucky and he picked traits on different 306 00:16:46,910 --> 00:16:48,310 chromosomes. 307 00:16:48,310 --> 00:16:50,820 But what about his next trait? 308 00:16:50,820 --> 00:16:52,640 Lucky again? 309 00:16:52,640 --> 00:16:53,440 Lucky again? 310 00:16:53,440 --> 00:16:57,380 Mendel studied seven traits. 311 00:16:57,380 --> 00:17:00,575 How many chromosome pairs do peas have? 312 00:17:03,100 --> 00:17:04,350 Turns out, seven. 313 00:17:08,619 --> 00:17:11,210 But anyway, what happens? 314 00:17:11,210 --> 00:17:12,190 What's going on? 315 00:17:12,190 --> 00:17:16,670 Mendel's second law can't be right if the chromosome theory 316 00:17:16,670 --> 00:17:20,040 is right when the genes are on the same chromosome. 317 00:17:20,040 --> 00:17:21,140 They would be dependent. 318 00:17:21,140 --> 00:17:24,530 They won't be independent one to one to one to one. 319 00:17:24,530 --> 00:17:26,550 So which is it? 320 00:17:26,550 --> 00:17:29,470 Is Mendel right, my hero? 321 00:17:29,470 --> 00:17:31,740 Or is this chromosome theory right? 322 00:17:31,740 --> 00:17:34,850 Because they can't be both perfectly right. 323 00:17:34,850 --> 00:17:38,060 So which is it? 324 00:17:38,060 --> 00:17:39,370 Oops, we've run out of time. 325 00:17:39,370 --> 00:17:40,960 [LAUGHTER] 326 00:17:40,960 --> 00:17:42,210 PROFESSOR: Next time.