Balancing Selection and Gene Flow

by Jason Amores Sumpter
217 views
1
1
Was this helpful ?
1
balancing selection is when No. One Lille is favored over the other. And this can sometimes be due to what's called the hetero zegas advantage, where hetero zegas individuals actually have an advantage over Hamas. I guess ones now. A great example of this is what the condition called sickle sell anemia. Oops and sickle cell anemia is caused by having two copies of a recess Ivo Lille, for a particular gene. Now you would think that because this disease is very, very harmful to a person's health, that these Leal's would be selected against that this disease would become very rare in the human population. And that's actually the case in many parts of the world, but notably in parts of the world where malaria, the mosquito borne disease, is prevalent. It's actually the presence of this. Alil is much more common, and that's because of the hetero zegas advantage. It turns out that people who are home a zegas dominant have a disadvantage to those who are hetero zegas. So hetero zygotes have both copies of the Lille, and so their blood cells look like this. They have a mix of the sickle cells and normal cells, so It turns out that these individuals fare better with malaria because the sickle cells give them a sort of natural defense to the disease. Whereas home, a zegas dominant individuals do not have that same advantage, and they're far more susceptible to the disease malaria. So that is the hetero zegas advantage, illustrated through sickle cell anemia. Now balancing selection can also occur due to frequency dependent selection, which is when certain Leal's are favored Onley when they are rare, meaning that certain wheels are favored when they are uncommon in the population. Unexamined of this is the wheels for coloration in guppies. Yeah, I know strange example, but particular Leal's that give guppies a rare coloration. A color that's not common in the population gives them an advantage when it comes to predation. You see, predators tend to learn to recognize the familiar shapes and colors of their prey, so guppies that have the common coloration the common Lille in the population are not favored, but the wheels that give rare colorations those air favored. However, if those a leal's for rare coloration become mawr common in the population, then they become less favored, so frequency dependent selection is when certainly eels are favored when they are rare and Onley when they are rare. Ecological selection is natural selection without any sexual selection. So essentially it's natural selection. It's when Onley ecological influences affect selection because sexual selection is out of the equation, meaning that we have relatively random mating, meaning that Onley ecological factors are going to affect the natural selection process. So gene flow is something we talked about Hardy Weinberg model. And this is the transfer of a Leal's from one population to another, potentially altering gene frequencies. That's the important part. You have a nice example of that here to populations of the same species of birds that are geographically separated by this mountain. But you have a little gene flow. You have one of these red birds, uh, mate with someone from pop the Bluebird population and sneak, it's alil into that population. It's little h alil. Into that population, you have one of these bluebirds made with red Bird and sneak its capital H alil into the red bird population, and that is gene flow, the transfer of wheels from one population to another. Now let's turn the page and talk about some other influences on genetic variation