MESS UP MY NOTES PART 3 Section 6
00:00:00TEACHER: Do you remember the lesson question? What are some different ways traits are inherited? Both incomplete dominance and codominance involve the interaction of two alleles. However, there are some traits that involve more than two alleles or more than one gene. Can you guess what it is?
00:00:20Well, this picture gives you a clue. Blood type is a trait affected by multiple alleles. Next, we will examine traits that are affected by more than two alleles and traits that are affected by more than one gene.
Section 7
00:00:00TEACHER: Let's start by looking at multiple alleles, which are three or more different forms of a gene for a single trait. Now, in the human population, there are four main blood types: A, B, AB, and O. So, the four blood types are determined by three alleles. Multiple alleles for blood types occur within the population.
00:00:31But individuals have only two of those alleles, one from each parent. So, let's take a closer look. The four blood types are a result of three alleles. Capital I superscript capital A, so I'll just call it IA, capital I superscript capital B or IB, and lowercase i. In this table, right here, you can see the blood types.
00:01:02Now, let's go through them together. Capital I superscript A or IA, IA, or IA lowercase i genotypes both result in blood type A, because A is dominant, and I is recessive. Here, capital I superscript B or IB, IB, or IB lowercase i genotypes both result in blood type B, because B is dominant, and I is recessive.
00:01:46Now, IA and IB genotype result in blood type AB because A and B are codominant. This type of blood is the rarest. The II or lowercase ii genotype results in blood type O, because I am recessive.
Section 9
00:00:00TEACHER: We have looked at traits affected by multiple alleles. We'll now look at an inheritance pattern controlled or affected by multiple genes. This type of inheritance pattern is called polygenic inheritance. Poly means many, so there are two or more genes
00:00:24that contribute to a single trait. So, for example, the birth weight of calves, as you can see here, looking for mama's milk, they are polygenic. When you think about it, it makes sense that there is one set of genes that controls the length of muscles, and a different set of genes that controls the length of bones. Now, remember, that humans can also be polygenic.
00:00:52What about the picture on the right? The length of corn ears is another example of a trait that is polygenic. Now, in human, there are several traits that we know to be polygenic such as eye color, skin color, and hair color. When traits are affected by many genes, many phenotypes are observed.
00:01:19Well, we can see this phenomenon in human eye color, as you can see in this image. Where there's a wide range of colors, including many that are a mixture. So, if I can point this to this person's eye, you can see the black in the center, and a little bit of brown, and beautiful mixture of blue.
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