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22. Evolutionary Genetics



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Hi in this video, we're gonna be talking about speciation. So speciation is the formation of a new species. And this occurs through a process called reproductive isolation. And so what is reproductive isolation? Well, if you've seen the hardy Weinberg videos, we talked about it little then. But I just wanna talk about it again here, reproductive isolation is various mechanisms that block reproduction between two individuals or two organisms. There's two types. There's pre psychotic and post psychotic, and these are named based on how they reference to the zygotes first cell that's formed. So pre psychotics happening to block reproduction before the zygotes formed. Post psychotic is happening to block um reproduction after the zygote is formed. So pre psychotic mechanisms. What are some examples of this? It could be different behavior. So one animal is nocturnal and one one is awake during the daytime, then they're most likely not going to make because they're not even if they live in the same environment and could otherwise make they're not going to be able to because they're not going to be awake at the same times. Um That's kind of temporal. You have different. Another example of behavior is just different mating dances, for instance. Or maybe some animals live in trees or fly and some live below ground. All of these things are going to block reproduction. There's mechanical blocks. And that's just that the parts don't fit together. So if the parts don't fit together, you can't make, there's not going to be reproduction. Um And then different types of gamete isolation where um the gametes are only produced at certain times and that may not be the time that the other organism is mating. Um Those types of situations post psychotic mechanisms happen after the offspring has been formed and usually they affect the reproductive success of the offspring itself. So examples of this are offspring in viability or sterility. And an example of this is mules, mules are made by mating between a horse and a donkey. Um These are two species that they can create a mule. So it's post psychotic mechanisms because the mules are sterile, they can't reproduce and therefore there's this reproductive isolation in which mules can't go on to produce more mules and they can't produce horses and they can't produce. Donkeys can't produce anything that made them. So um there is this concept called the biological species concept that describes the difference is necessary to consider two organisms different species. And you may think, oh, that's fairly easy. Like it's whether or not they can reproduce. But it actually can be more difficult because technically horses and donkeys can reproduce together, but they only create offspring there and create meals that are sterile. And so deciding what those features are about to species that make them two separate species can be difficult. But this concept seeks to identify what are the differences and what how when can we say, this is one species and this is another and they're completely separate species. So an example of this process. So you start out with this initial sample of flies and then in a laboratory setting just to like facilitate evolution in a laboratory setting, you separate the flies and you give them to different types of media or two different types of food sources. One food source has a lot of starch, one has a lot of the small toe sugar. And eventually over time after several generations you get actually these two different flies. You see there's the yellow flies here and the brown flies here and if you put them back together, what you'll find is that sometimes these won't make even though they started out as the same species. This reproductive isolation by this barrier and also by this food source after several generations has actually led to two separate fly species of yellow and brown. Now there are two types of speciation. There's actually a little bit more than this, but there's two types that we're going to mention in this class. And that's ala Patrick and Saint Patrick's. Ala Patrick speciation occurs when a geographic barrier is present and that splits whatever population there was into two groups. And because that barrier is there, it's either it's either distance, could be like a mountain or a river or anything that's going to physically separate two populations. Um there won't be able to exchange genetic information because they can't overcome that barrier whether it's distance or a mountain airstream sim Patrick speciation is different because there's no barrier there or there's no geographic barrier, but there's some other type of reproductive isolation happening that isn't an actual geographic barrier. Um And that can be something like um maybe the food source changed and therefore um one species more out to find food and trees and one more out to find food underground. And that actually separates them in an absence of a barrier, right? Because those species could potentially come out of the trees or come out of the ground and see each other in eight, they just don't because there's some other type of reproductive isolating mechanism present that's keeping them separate and allowing them to evolve separately and accumulate these variations that eventually will result in them becoming two different species. So for example, here, ala Patrick speciation. You start off with this one homogeneous group of organisms in blue. A barrier is formed here in black um events that isolates them. And so this half of the population begins developing this green variation while the other half remains the same. And eventually they developed two different species, a green species and a blue species that even once the barrier is removed and they can overlap together is shown here, that doesn't mean that they're going to be there still two separate species. They won't be able to reproduce and they won't be able to create offspring together even though they originally could. But it's that barrier forming these isolation that allows them to develop different types of genetic variation that actually develops them into two separate species, so that is speciation and how these new species are created through evolution. So with that, let's now move on.

Which of the following is an example of a postzygotic reproductive isolation mechanism?


Which type of speciation occurs when a geographic barrier splits the population into two or more groups?