Biology Chapter 24 Objectives

Biology Chapter 24 Objectives - Chapter 24 The Origin of...

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Chapter 24 The Origin of Species What Is a Species? 1. Anagenesis is the accumulation of heritable changes, altering the characteristics of a species. Cladogenesis is branching evolution, in which a new species arises from a population that buds from a parent species. 2. Ernst Mayr’s biological species concept defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but are unable to produce viable, fertile offspring with members of other populations. 3. Prezygotic barriers impede mating between species or hinder the fertilization of ova if members of different species attempt to mate. If a sperm cell from one species does overcome prezygotic barriers and fertilizes an ovum from another species, postzygotic barriers also prevent the hybrid zygote from developing into a viable, fertile animal. 4. The five prezygotic isolating mechanisms are: 1) Habitat Isolation, when 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. Two species of garter snakes occur in the same geographic areas, but one lives mainly in water while the other is primarily terrestrial. 2) Temporal Isolation, when species that breed during different times of the day, different seasons, or different years cannot mix their gametes. In North America, the geographic ranges of the eastern spotted skunk and the western spotted sunk overlap, but one mates in late winter and the other mates in late summer. 3) Behavioral Isolation, when courtship rituals that attract mates and other behavior unique to a species are effective reproductive barriers, even between closely related species. Blue-footed boobies, mate only after a courtship display unique to their species. 4) Mechanical Isolation, when morphological differences can prevent successful mating. Flowers often have distinct appearances that attract different pollinators. Thus, cross-pollination between the plants does not occur. 5)
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This note was uploaded on 08/29/2009 for the course BIOL 101 taught by Professor Sakji during the Fall '08 term at Linn Tech.

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Biology Chapter 24 Objectives - Chapter 24 The Origin of...

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