1 00:00:00,160 --> 00:00:02,760 Okay. This problem can be a little tricky if you're 2 00:00:02,760 --> 00:00:06,470 not used to figuring questions like this out, backwards. But 3 00:00:06,470 --> 00:00:09,170 this is the best way to learn. Instead of giving 4 00:00:09,170 --> 00:00:12,120 you all the numbers and have you plug them into equations, 5 00:00:12,120 --> 00:00:14,090 it's better to have you work backwards like this. 'because 6 00:00:14,090 --> 00:00:17,100 you really get to see the patterns that emerge. So 7 00:00:17,100 --> 00:00:19,960 let's take the easy part first. We know that if 8 00:00:19,960 --> 00:00:24,834 we have no lactase non-persistent, no lactose intolerant people, zero, 0%. 9 00:00:24,834 --> 00:00:28,980 That represents our homozygous recessive condition. So 10 00:00:28,980 --> 00:00:31,480 we gotta have zero in that group. There 11 00:00:31,480 --> 00:00:36,360 are no people in our population that have that genotype. Okay, so now that means 12 00:00:36,360 --> 00:00:38,290 we gotta split 1000 people between these 13 00:00:38,290 --> 00:00:42,930 two genotypes, homozygous dominant and heterozygous. The only 14 00:00:42,930 --> 00:00:45,850 scenario I can calculate that gives me this 15 00:00:45,850 --> 00:00:50,560 particular allelic frequency is 500 in each group. 16 00:00:50,560 --> 00:00:53,060 So remember both of these are lactase 17 00:00:53,060 --> 00:00:57,354 persistent, so together that's everybody 100% are 18 00:00:57,354 --> 00:01:00,990 lactase persistence. But we need a number 19 00:01:00,990 --> 00:01:03,740 to get our allelic frequencies to 0.75 for 20 00:01:03,740 --> 00:01:09,200 the dominant allele. And 0.25 for the recessive allele, so if we go to our 21 00:01:09,200 --> 00:01:15,570 equation here and set it up toward backwards. 0.75 equals, we have the total 22 00:01:15,570 --> 00:01:18,110 number of alleles, so how many total 23 00:01:18,110 --> 00:01:20,910 dominant alleles are we dealing with here? This 24 00:01:20,910 --> 00:01:28,870 would be X equals 1500. We've got to have 1500 dominant alleles in here. We do 25 00:01:28,870 --> 00:01:34,770 the same thing with the recessive allele, we gotta have 500. Well, if we have to 26 00:01:34,770 --> 00:01:38,440 have 500 recessive alleles. The only way I'm 27 00:01:38,440 --> 00:01:41,570 going to get 500, is in this heterozygous condition. 28 00:01:41,570 --> 00:01:43,860 'because I don't have any homozygous recessive. So 29 00:01:43,860 --> 00:01:47,070 that means, to get 500 recessive alleles, I've gotta 30 00:01:47,070 --> 00:01:49,720 have 500 heterozygous individuals so that I get 31 00:01:49,720 --> 00:01:53,660 500 of these. 500 heterozygous individuals then makes up 32 00:01:53,660 --> 00:01:56,265 500 of my dominants, as well. I need 33 00:01:56,265 --> 00:01:59,783 1,500 total. So subtract 500 from 1,500. I need 34 00:01:59,783 --> 00:02:03,960 1,000 more alleles. 500 in this box takes care 35 00:02:03,960 --> 00:02:06,690 of 1,000, right? Because I get 500 of both. 36 00:02:06,690 --> 00:02:08,990 500 of the first dominant and 500 of the second 37 00:02:08,990 --> 00:02:14,030 dominant. Easy, huh? Or hard, depending on your perspective. I 38 00:02:14,030 --> 00:02:16,240 really hope you understand this. If you don't, if you 39 00:02:16,240 --> 00:02:19,460 have trouble, it's okay. There's not a lot of this course 40 00:02:19,460 --> 00:02:22,970 that's going to deal with too much allelic frequencies. But I 41 00:02:22,970 --> 00:02:24,850 do want to focus on it a bit more for the 42 00:02:24,850 --> 00:02:27,240 rest of the lesson. If you can really get a 43 00:02:27,240 --> 00:02:31,980 grasp of these allelic frequencies, you're going to have a whole new 44 00:02:31,980 --> 00:02:35,740 appreciation for understanding gene flow, genetic 45 00:02:35,740 --> 00:02:39,150 drift, and looking at huge populations of 46 00:02:39,150 --> 00:02:42,010 individuals. And seeing how alleles travel 47 00:02:42,010 --> 00:02:45,650 through. And can be shaped by evolution.