Video transcriptHave you ever wondered how we classify different organisms into different species? Well, before we look at that, let's go over the difference between asexual reproduction and sexual reproduction. In asexual reproduction, one organism, like a single bacterium, will divide into two daughter cells that are both genetically identical to the original cell. In sexual reproduction, two members of the same species will reproduce together in order to form genetically unique offspring. Now, in general, we say that organisms that reproduce asexually usually have low genetic diversity, whereas sexually reproducing species have high genetic diversity. So what is a species? Now, this can be a very difficult question to answer. For sexually reproducing organisms, we can say that two organisms, like this cat and this human, are members of different species. They're unable to have offspring together. However, for asexually reproducing organisms, like bacteria, protists, and archaea, it's a little more confusing. These species don't mate with other organisms. So we have a difficult time classifying them into different categories. And we call this the species problem. But in this video, we're going to spend time just looking at those sexually reproducing organisms. And these are separated into different species by different forms of what we call reproductive isolation. And this is the idea that there are many forces that stop two different organisms from having offspring together. And we can divide these forces into two separate categories, pre-zygotic forms and post-zygotic forms. Pre-zygotic isolation refers to all the different forces that prevent two organisms from having offspring together that occur prior to the formation of a zygote. And remember that a zygote is a single cell that is made up of the genetic material of both organisms that have reproduced together. Post-zygotic forms of isolation we'll get into a little bit later. So the first type of pre-zygotic isolation is temporal/habitat isolation. And temporal isolation refers to the fact that not all organisms mate at the same time. Some may mate at night, while others mate during the day. Some may mate in spring, while others mate in winter. If two organisms do not find mates at the same time, then they are temporally isolated. Habitat isolation refers to the place where the organisms mate. Some may prefer mating in the forest, while others prefer mating in the mountains. And if two organisms don't find mates in the same place, then they are also isolated. If time and place aren't a problem, then the next barrier is behavioral isolation, which refers to mate selection and how organisms go about attracting a mate. Now, not all organisms will attract a mate the same way. Perhaps one animal, like a bird, will attract a mate by singing a song, whereas this bunny rabbit may do a little dance to attract a mate. So we have behavioral isolation. And now we have mechanical isolation, which deals with the physical inability of two organisms to mate, even if they wanted to. Now, a great example of this is a huge animal like an elephant being unable to mate with a tiny mouse. If two organisms do mate successfully, they may still encounter gametic isolation, which is when fertilization between the two gametes to form a zygote is impossible. Now, once the zygote has been formed, we can move on and look at post-zygotic forms of reproductive isolation. And the first form is zygote mortality. And this occurs when even if the two gametes from the two organisms can fuse successfully and form a zygote, that zygote would have a high mortality rate and be unable to develop into a mature offspring. Next we have hybrid inviability, which occurs when a zygote is able to grow into a mature offspring, but that offspring will have a high mortality rate and won't be able to grow into a mature adult. Finally, we have the last form of reproductive isolation, which is hybrid sterility. And this is when the offspring can grow into a mature adult. But that mature adult is not able to mate and have offspring of its own. So if two sexually reproducing organisms are not isolated by any of these barriers, then we can generally say that they are members of the same species. So what did we learn? Well, first we learned about the species problem and how classifying different organisms into different species can be quite difficult. We have a pretty good definition for sexually reproducing organisms, but not really for asexually reproducing organisms. And next we learned about reproductive isolation and how we can say that two sexually reproducing organisms are reproductively isolated if they are unable to freely produce fertile offspring together. Show Reproductive isolation, through mechanical, behavioral, and physiological barriers, is an important component of speciation. Learning Objectives
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Reproductive IsolationGiven enough time, the genetic and phenotypic divergence between populations will affect characters that influence reproduction: if individuals of the two populations were to be brought together, mating would be improbable, but if mating did occur, offspring would be non-viable or infertile. Many types of diverging characters may affect reproductive isolation, the ability to interbreed, of the two populations. Reproductive isolation is a collection of mechanisms, behaviors, and physiological processes that prevent the members of two different species that cross or mate from producing offspring, or which ensure that any offspring that may be produced is not fertile. Scientists classify reproductive isolation in two groups: prezygotic barriers and postzygotic barriers. Recall that a zygote is a fertilized egg: the first cell of the development of an organism that reproduces sexually. Therefore, a prezygotic barrier is a mechanism that blocks reproduction from taking place; this includes barriers that prevent fertilization when organisms attempt reproduction. A postzygotic barrier occurs after zygote formation; this includes organisms that don’t survive the embryonic stage and those that are born sterile. Some types of prezygotic barriers prevent reproduction entirely. Many organisms only reproduce at certain times of the year, often just annually. Differences in breeding schedules, called temporal isolation, can act as a form of reproductive isolation. For example, two species of frogs inhabit the same area, but one reproduces from January to March, whereas the other reproduces from March to May.  In some cases, populations of a species move to a new habitat and take up residence in a place that no longer overlaps with other populations of the same species; this is called habitat isolation. Reproduction with the parent species ceases and a new group exists that is now reproductively and genetically independent. For example, a cricket population that was divided after a flood could no longer interact with each other. Over time, the forces of natural selection, mutation, and genetic drift will likely result in the divergence of the two groups. Behavioral isolation occurs when the presence or absence of a specific behavior prevents reproduction from taking place. For example, male fireflies use specific light patterns to attract females. Various species display their lights differently; if a male of one species tried to attract the female of another, she would not recognize the light pattern and would not mate with the male. Other prezygotic barriers work when differences in their gamete cells prevent fertilization from taking place; this is called a gametic barrier. Similarly, in some cases, closely-related organisms try to mate, but their reproductive structures simply do not fit together. For example, damselfly males of different species have differently-shaped reproductive organs. If one species tries to mate with the female of another, their body parts simply do not fit together.. In plants, certain structures aimed to attract one type of pollinator simultaneously prevent a different pollinator from accessing the pollen. The tunnel through which an animal must access nectar can vary in length and diameter, which prevents the plant from being cross-pollinated with a different species. When fertilization takes place and a zygote forms, postzygotic barriers can prevent reproduction. Hybrid individuals in many cases cannot form normally in the womb and simply do not survive past the embryonic stages; this is called hybrid inviability. In another postzygotic situation, reproduction leads to the birth and growth of a hybrid that is sterile and unable to reproduce offspring of their own; this is called hybrid sterility. What is reproductive isolation give an example?Reproductive Isolation Examples
Two closely related species of fish who live in different habitats not mating. Fruit flies of two different species excreting different pheromones. Fertilization between a tiger and a leopard, creating a zygote that does not develop.
What is reproductive isolation?Reproductive isolation is a collection of mechanisms, behaviors, and physiological processes that prevent the members of two different species that cross or mate from producing offspring, or which ensure that any offspring that may be produced is not fertile.
What are 3 types of reproductive isolation with examples?These include temporal isolation, ecological isolation, behavioral isolation, and mechanical isolation. Post-zygotic barriers: barriers that come into play after two species have mated. These include genetic incompatibility, zygotic mortality, hybrid inviability, hybrid sterility, and hybrid breakdown.
What is reproductive isolation Class 11?Reproductive isolation refers to the situation where different species may live in the same area, but properties of individuals prevent them from interbreeding. The things which stop species or groups of organisms reproducing sexually are called isolating mechanisms.
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