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3. Extensions to Mendelian Inheritance


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Hi in this video, we're gonna talk about play a trophy. So play a trophy. It's defined by when a single gene has multiple effects on the phenotype of an organism. So this is when you have a single gene and say it's mutated or something and that gives you a lot of different types. Could give you breast cancer or and um, you know, neurological defects or um, you know, short short fingers and difficulty breathing. And these are two completely different regions of the body with different athena typically effects, but it's the same gene causing them. So the way that a single gene um could affect an organism in multiple ways is through three main ways. The first is that the genes expression just has multiple functions, right? You know, the gene, for instance, is involved in two pathways and both of those pathways lead to different functions. Second way is that the gene is expressed in different cell types. So, say if the gene is expressed in um the kidney and the brain, then you're going to get effects in the kidney and you're gonna get effects in the brain, but maybe nowhere else. And so that's how um that could work where a single gene is having multiple effects because it's only expressed in these two areas and not just everywhere in the body all the time. And the third way this could happen is it's expressed in different stages of development. So, for instance, a mutated gene could have an effect during the first year of life and then sort of die down and then show up again at age 50 and that's because there There is a different developmental period in which this gene is expressed either early in life or middle aged and therefore those different stages of development, the same gene is obviously gonna have different effects because a one year old is very different than a 50 year old. So those are the three ways that play a trophy can occur. Now, a good example of this is going to be cystic fibrosis. You may have heard of cystic fibrosis. It's a it's a pretty like not fun disease to have. Um And the what causes it is a mutation in a gene which produces a protein called CFTR. Now what a CFTR CFTR protein. It's a trans membrane protein, meaning that exists in the membrane and it has a big function in regulating chloride concentration. Now this is super important because your cells need certain levels of chloride to do certain functions. And so if it's not being regulated correctly because you have a mutation then you're gonna get a lot of phenotype. So for instance when it's mutated, it no longer regulates chloride concentrations, correct? So when chloride concentrations are messed up that messes up lots of different things which cause different phenotype. So for instance, lungs have a thick mucus because that chloride concentration is super um responsible for making sure that fluid uptake and intake in the lungs is regulated and salt concentrations are regulated. So you end up with a thick mucus and lung, you end up with very salty sweat on your face, or your under arms or your arms. Um and then there's a ton of other issues that sort of chloride imbalances causes in the body. Now this is one mutation in one gene but it causes multiple phenotype. So so that's an example of a trophy. So here's just what CFTR. I didn't really have a good image for this. You don't need to know any of like what these terms are anything like that. But I didn't really have a good image but I wanted to show you something. So it's not just text. So here's CFTR you can see it's a trans membrane protein because it's in the membrane and um when this is not working right, chloride is not distributed on each side of the membrane properly concentrations get messed up and that causes different phenotype in different regions of the body. So that's play trophy with that. Let's not move on.

Which of the following is NOT an example of a pleiotropic trait?


A pleotropic trait is controlled by…