Reproductive isolation is the existence of biological factors barriers that

Reproductive isolation is the existence of biological

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Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring Prezygotic and postzygotic barriers Prezygotic barriers block fertilization from occurring by Impeding different species from attempting to mate Preventing the successful completion of mating Hindering fertilization if mating is successful Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult by Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown 4. Explain the difference between allopatric and sympatric speciation In allopatric speciation , gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations For example, the flightless cormorant of the Galápagos likely originated from a flying species on the mainland In sympatric speciation , speciation occurs in populations that live in the same geographic area 5. Explain the three ways that sympatric speciation can occur Sympatric speciation can occur if gene flow is reduced by factors such as: Polyploidy (ex: 2n vs 4n) Sexual selection Habitat differentiation 6. Explain what the fossil records shows about the rate of speciation over time The fossil record includes examples of species that appear suddenly, persist unchanged for some time, and then disappear
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Chapter 25 Learning Objectives: 1. Explain what conditions were like on early earth. Earth’s early atmosphere had little oxygen and likely contained water vapor and chemicals released by volcanic eruptions For example, nitrogen and its oxides, carbon dioxide, methane, ammonia, hydrogen 2. List the stages hypothesized to lead to the formation of early cells. Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages Abiotic synthesis of small organic molecules Joining of these small molecules into macromolecules Packaging of molecules into protocells Origin of self-replicating molecules 3. Explain why the first genetic material was most likely RNA. In 2013, Dr Szostak and his colleagues constructed a vesicle whose RNA could self-replicate within the vesicle If a vesicle on early Earth could grow, split, and pass on its RNA to its “daughters,” the daughters would be protocells The most successful of the early protocells could have increased through natural selection RNA could have provided the template for the formation of DNA Double-stranded DNA is more chemically stable and can be replicated more accurately than RNA 4. Describe how fossils are formed and different methods of dating fossils. Sedimentary rocks are deposited into layers called strata and are the richest source of fossils The age of a fossil can be determined using radiometric dating A radioactive “parent” isotope decays to a “daughter” isotope at a characteristic rate Each isotope has a known half-life , the time required for half the parent isotope to decay
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