WEBVTT 1 00:00:00.584 --> 00:00:04.751 Phenotypes, Genotypes, and Incomplete Dominance. 2 00:00:05.917 --> 00:00:08.645 So, first let's talk about what the terms genotype 3 00:00:08.645 --> 00:00:10.385 and phenotype mean. 4 00:00:10.385 --> 00:00:13.806 Genotype is the set of alleles possessed by an organism. 5 00:00:13.806 --> 00:00:16.948 You can just remember the genes, genotype. 6 00:00:16.948 --> 00:00:19.804 Recessive information is present in the genotype. 7 00:00:19.804 --> 00:00:24.102 So, AA, that means you're homozygous dominant 8 00:00:24.102 --> 00:00:26.358 with two capital A's. 9 00:00:26.358 --> 00:00:30.093 Big capital A lowercase a, heterozygous, 10 00:00:30.093 --> 00:00:33.876 meaning you've got a dominant as well as a recessive. 11 00:00:33.876 --> 00:00:37.351 Or you could see lowercase a lowercase a, 12 00:00:37.351 --> 00:00:41.518 which is heterozy, or homozygous, I should say, recessive. 13 00:00:42.501 --> 00:00:45.807 So, in the latter two cases there that we just looked at, 14 00:00:45.807 --> 00:00:49.594 we see the recessive information is present there 15 00:00:49.594 --> 00:00:51.427 in the genotype. 16 00:00:51.427 --> 00:00:55.026 Phenotype is a set of traits expressed in an organism, 17 00:00:55.026 --> 00:00:58.948 so it's what is the traits not the alleles. 18 00:00:58.948 --> 00:01:00.908 Traits are what we actually see, 19 00:01:00.908 --> 00:01:04.678 so we see someone's blue eyes or their brown hair. 20 00:01:04.678 --> 00:01:07.807 The alleles that code for that, we don't see. 21 00:01:07.807 --> 00:01:10.449 Recessive information typically will not be shown 22 00:01:10.449 --> 00:01:12.550 in the phenotype, it's there in the genotype, 23 00:01:12.550 --> 00:01:15.740 but usually the dominance, the dominant trait 24 00:01:15.740 --> 00:01:17.966 is where it's expressed and that's all we see. 25 00:01:17.966 --> 00:01:22.384 So, for example, earlobes, attached or detached earlobes. 26 00:01:22.384 --> 00:01:24.833 The phenotype is what we actually see, 27 00:01:24.833 --> 00:01:27.168 are they attached or detached, the trait. 28 00:01:27.168 --> 00:01:31.085 The genotype is AA co-dominant, Aa heterozygous 29 00:01:33.335 --> 00:01:37.308 where the capital A is still dominant, 30 00:01:37.308 --> 00:01:39.853 or lowercase a lowercase a as we see at the top 31 00:01:39.853 --> 00:01:43.363 of the diagram here, which is homozygous recessive. 32 00:01:43.363 --> 00:01:45.573 So, in both of the lowercases there, 33 00:01:45.573 --> 00:01:50.086 the capital A capital A, or the capital A lowercase a, 34 00:01:50.086 --> 00:01:53.307 the dominant trait of detached earlobes wins out 35 00:01:53.307 --> 00:01:55.074 and the trait that is shown, 36 00:01:55.074 --> 00:01:57.991 the phenotype is detached earlobes. 37 00:01:59.592 --> 00:02:03.429 But in the case where there are two recessive alleles, 38 00:02:03.429 --> 00:02:06.762 so the genotype is homozygous recessive, 39 00:02:07.662 --> 00:02:12.384 then we see that the demonstration or the expression of 40 00:02:12.384 --> 00:02:16.474 the recessive trait, which is attached earlobes, 41 00:02:16.474 --> 00:02:18.255 so the phenotype is attached. 42 00:02:18.255 --> 00:02:20.951 So, understanding the difference in those two terms 43 00:02:20.951 --> 00:02:22.254 is really important, 44 00:02:22.254 --> 00:02:24.531 because often on the exam they'll ask you things they, 45 00:02:24.531 --> 00:02:28.364 they get at your knowledge of what those mean. 46 00:02:30.133 --> 00:02:33.182 Now, there are some rare cases where dominance 47 00:02:33.182 --> 00:02:34.280 is not complete. 48 00:02:34.280 --> 00:02:38.090 So, incomplete dominance means the dominant allele 49 00:02:38.090 --> 00:02:40.374 is not completely dominant. 50 00:02:40.374 --> 00:02:43.537 Instead, the two traits basically blend. 51 00:02:43.537 --> 00:02:46.358 So, red petals and white petals, 52 00:02:46.358 --> 00:02:48.252 maybe red petals are dominant, 53 00:02:48.252 --> 00:02:50.347 but they're incomplete in their dominance, 54 00:02:50.347 --> 00:02:52.847 so we end up with pink petals. 55 00:02:55.070 --> 00:02:57.460 You'll only see this with heterozygous individuals 56 00:02:57.460 --> 00:02:59.885 where you have one dominant and one recessive, 57 00:02:59.885 --> 00:03:02.392 and then the dominant allele does not completely dominate 58 00:03:02.392 --> 00:03:05.865 and you have partial expression of the recessive trait 59 00:03:05.865 --> 00:03:08.616 and it blends with the dominant trait 60 00:03:08.616 --> 00:03:12.460 to create this new expression of this new trait. 61 00:03:12.460 --> 00:03:13.738 With homozygous individuals, 62 00:03:13.738 --> 00:03:16.013 they'll still show normal dominance. 63 00:03:16.013 --> 00:03:19.309 So, if you get a red allele and a red allele, 64 00:03:19.309 --> 00:03:22.719 then you're gonna obviously have that dominant red color, 65 00:03:22.719 --> 00:03:24.773 and if you get two recessives you're gonna have 66 00:03:24.773 --> 00:03:26.479 the recessive color of white, 67 00:03:26.479 --> 00:03:30.646 or whichever one happens to be dominant and recessive. 68 00:03:31.513 --> 00:03:34.246 There's also a situation in which we call codominance, 69 00:03:34.246 --> 00:03:37.021 which is a little different than incomplete dominance. 70 00:03:37.021 --> 00:03:39.268 Codominance occurs when an organism expresses 71 00:03:39.268 --> 00:03:43.423 both of the traits in the case of heterozygotes. 72 00:03:43.423 --> 00:03:46.555 So, meaning you get a dominant and a recessive, 73 00:03:46.555 --> 00:03:49.928 but they basically are both kinda dominant, 74 00:03:49.928 --> 00:03:52.433 so there's not really one that's actually recessive 75 00:03:52.433 --> 00:03:54.100 in the common sense. 76 00:03:55.358 --> 00:03:57.950 So, to go back to the flowers, 77 00:03:57.950 --> 00:03:59.890 this would be a case which does happen 78 00:03:59.890 --> 00:04:02.566 in certain kinds of flowers where a red and a white 79 00:04:02.566 --> 00:04:06.153 cross pollinate, and instead of getting pink 80 00:04:06.153 --> 00:04:09.797 you get some red petals and some white petals. 81 00:04:09.797 --> 00:04:12.519 So, in that case we have codominance, 82 00:04:12.519 --> 00:04:14.813 and that's how it differs from incomplete dominance. 83 00:04:14.813 --> 00:04:17.104 With incomplete dominance you got all pink petals, 84 00:04:17.104 --> 00:04:20.730 with codominance you got some red petals, some white petals. 85 00:04:20.730 --> 00:04:25.338 Another example of codominance is the idea of blood typing. 86 00:04:25.338 --> 00:04:29.505 With someone with blood type AB shows both A and B antigens, 87 00:04:32.107 --> 00:04:34.774 so in this case someone with AB, 88 00:04:35.669 --> 00:04:37.028 because they have both antigens, 89 00:04:37.028 --> 00:04:41.400 they can take donations of blood that are A or B, 90 00:04:41.400 --> 00:04:42.935 or of course AB. 91 00:04:42.935 --> 00:04:45.185 But in the case of group O, 92 00:04:46.148 --> 00:04:47.600 a blood type O, they, 93 00:04:47.600 --> 00:04:49.982 that is basically corecessive, 94 00:04:49.982 --> 00:04:53.283 so it's just both of the recessive genes show up there, 95 00:04:53.283 --> 00:04:56.560 so there's no A antigens or B antigens, 96 00:04:56.560 --> 00:04:59.760 so group O can donate to any of them 97 00:04:59.760 --> 00:05:01.146 without being rejected, 98 00:05:01.146 --> 00:05:04.890 but it can only receive blood from other O's. 99 00:05:04.890 --> 00:05:09.057 So, that's why we usually call AB the universal recipient 100 00:05:10.936 --> 00:05:14.196 and blood type O the universal donor. 101 00:05:14.196 --> 00:05:17.802 So, this is just a practical kind of application 102 00:05:17.802 --> 00:05:21.565 where you see in use the idea of codominance 103 00:05:21.565 --> 00:05:23.815 and the effect that it has.