My Chapter 26 notes

My Chapter 26 notes - Morgan Mains Biology 1202 Chapter 24...

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Morgan Mains Biology 1202 Chapter 24 and 26 Chapter 24 – The Origin of Species There are millions of species on Earth… How do we define a species? There are many animals that look very similar but are differing species. Take the Hummingbirds of Costa Rica for example: Species Biological Species Concept : A population whose members can potentially interbreed in nature to produce viable offspring Reproductive Barriers isolate populations from one another. o Pre-Zygotic vs. Post-Zygotic A complete barrier would result in no gene flow. An incomplete barrier could still reduce gene flow.
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o Pre-Zygotic Barriers Habitat isolation Geographic isolation o Two species that occupy different habitats within the same area may encounter each other rarely, if at all, even though they are not isolated by obvious physical barriers, such as mountain ranges. o Ex: Different butterfly species exist in different geographic locations and they are isolated. Ecological Isolation o Ex: One species of an animal may live in the water while the other primarily on land (garter snakes). Behavioral (mate choice) isolation Courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barriers, even between closely related species. Such behavioral rituals enable mate recognition , a way to identify potential mates of the same species. o Ex: Male blue-footed boobies attract females by attracting their attention to his bright blue feet. Temporal isolation Species that breed during different times of the day, different seasons, or different years cannot mix their gametes. o Eastern spotted skunk mates in late winter while the Western spotted skunk mates in late summer. Mechanical isolation Mating is attempted, but morphological differences prevent its successful completion. o The shells of two snails have spirals pointing in opposite directions so mating cannot be completed. Gametic Isolation The sperm of one egg may not be able to fertilize the eggs of another species. For instance, sperm may not be able to survive in the reproductive tracts of females of the other species, or biochemical mechanisms prevent the sperm from penetrating the membrane surrounding the other species’ eggs.
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o Separates closely related species of aquatic animals such as sea urchins Red and purple sea urchins cannot mate Pre-Zygotic Barriers block fertilization from occurring. o Post-Zygotic Barriers Reduced Hybrid Viability The genes of different parent species may interact in ways that impair the hybrid’s development or survival in its environment o Many hybrids don’t complete development or are very frail Reduced Hybrid Fertility Even if hybrids are vigorous, they may be sterile. If the chromosomes of the two parent species differ in number or structure, meiosis in the hybrids may fail to produce normal gametes. Since the infertile hybrids cannot produce offspring when they mate with either parent species, genes cannot flow freely between the species
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My Chapter 26 notes - Morgan Mains Biology 1202 Chapter 24...

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