HW #24 - AP Biology Period 4#22 Liem Nguyen...

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AP Biology Period – 4 #22 Liem Nguyen 12/12/09 Homework #24 (091218): Chapter 24 (due Friday 091218 ) Total points: 30 points for Attempt on all questions 10 points for concept map Objectives What Is a Species? 1. Distinguish between anagenesis and cladogenesis. Anagenesis: phylic evolution Cladogenesis: branching evolution While anagenesis is the accumulation of changes that gradually transform one species to another, cladogenesis is the splitting of a gene pool into two or more separate pools, each giving rise to one or more new species. 2. Define Ernst Mayr’s biological species concept. Potential to interbreed and produce fertile offspring with same species Unable to do above with different species The 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. Distinguish between prezygotic and postzygotic isolating mechanisms. Prezygotic barriers: impede mating between species or hinder the fertilization of ova if members of different species attempt to mate Postzygotic barriers: prevent the hybrid zygote from developing into a viable, fertile adult Prezygotic barriers try and prevent the sperm from attaching to the egg and producing a zygote. But if this does not succeed, postzygotic barriers take over and prevent the zygote from developing into a fertile adult. 4. Describe five prezygotic isolating mechanisms and give an example of each. Habitat isolation: separated geographically Temporal isolation: mating times differ Behavioral isolation: mating rituals differ Mechanical isolation: color and shape in plants Gametic isolation: sperm is unable to fertilize egg Two species of garter snakes are separated geographically because one lives in the water while the other lives on land. The eastern spotted skunk and the western spotted skunk’s mating times differ. The blue-footed boobies mate only if a ritual is performed.
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Mechanical isolation is displayed through monkey flowers, which differ in shapes and colors. Finally, a male sea urchin’s sperm are unable to reach the egg of the female of another species. 5. Explain a possible cause for reduced hybrid viability. Reduced hybrid viability: genes of parent species impair the hybrid’s development One possible cause of reduced hybrid viability is that the genes of the parents do not allow the hybrid offspring to complete development, leaving it to be very frail. 6. Explain how hybrid breakdown maintains separate species even if fertilization occurs. Hybrid breakdown: causes next generation to be feeble or sterile After the first generation of hybrids occurs, they may mate, but if fertilization occurs, the following generation will be either feeble or sterile. This results in a group of hybrids with each generation becoming weaker and weaker.
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This note was uploaded on 11/06/2011 for the course AP BIO 101 taught by Professor Chan during the Fall '05 term at JFK.

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HW #24 - AP Biology Period 4#22 Liem Nguyen...

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