Hi. In this video, we're going to talk about pleiotropy. So pleiotropy is defined by when a single gene has multiple effects on the phenotype of an organism. This is when you have a single gene and, say, it's mutated or something, and that gives you a lot of different phenotypes. It could give you, you know, breast cancer or neurological defects or short fingers and difficulty breathing. These are two completely different regions of the body with different phenotypic effects, but it's the same gene causing them. So the way that a single gene could affect an organism in multiple ways is through three main methods. The first is that the gene's expression just has multiple functions. Right? For instance, the gene is involved in two pathways, and both of those pathways lead to different functions. The second way is that the gene is expressed in different cell types. So say if the gene is expressed in the kidney and the brain, then you're going to get effects in the kidney and the brain, but maybe nowhere else. And that's how it 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. The third way this could happen is if it's expressed in different stages of development. 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 was a different developmental period in which this gene is expressed either early in life or middle age. And, therefore, those different stages of development, the same gene is obviously going to have different effects because a one-year-old is very different from a fifty-year-old. So those are the three ways that pleiotropy can occur.
Now a good example of this is going to be cystic fibrosis. You may have heard of cystic fibrosis. It's a pretty unpleasant disease to have. The cause is a mutation in a gene, which produces a protein called CFTR. Now what is CFTR? CFTR is a protein. It's a transmembrane protein, meaning that it exists in the membrane. And it has a big function in regulating chloride concentration. Now, this is super important because your cell needs certain levels of chloride to perform certain functions, and so if it's not being regulated correctly because you have a mutation, then you're going to get a lot of phenotypes. So, for instance, when it's mutated, it no longer regulates chloride concentrations correctly. So when chloride concentrations are messed up, that interferes with lots of different things, which cause different phenotypes. For instance, lungs have a thick mucus because that chloride concentration is super responsible for making sure that fluid uptake and intake in the lungs is regulated and salt concentrations underarms. And then, your underarms, or your arms. And then there are a ton of other issues that sort of chloride imbalances cause in the body. Now this is one mutation in one gene, but it causes multiple phenotypes, so that's an example of pleiotropy.
