BSsqans-lect08 metazophylo&devel

BSsqans-lect08 metazophylo&devel - BIS 1B (Winter...

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BIS 1B (Winter 2008) Answers to Study Questions: Metazoan phylogeny and development Lecture 8 1. What is the difference between a clade and a monophyletic group? Both refer to the same thing: a clade (or monophyletic group) is a group of organisms that are all descended from a particular common ancestor. Moreover, the clade (or monophyletic group) includes all the descendants of that ancestor. 2. Distinguish between anagenesis and cladogenesis. Anagenesis is evolution within populations (within evolutionary lineages), often called microevolution. Cladogenesis is the genesis of two or more species (or evolutionary lineages) from one; the splitting event is called speciation. 3. Compare and contrast the biological species concept with the phenetic (or morphological) species concept. Discuss the strengths and weaknesses of each. Which is most appropriate for asexual organisms? The biological species concept (BSC) states that a species is a population or set of populations that is reproductively isolated from others. The BSC is consistent with the idea that speciation occurs when related populations diverge from one another and acquire characteristics that cause them to be reproductively isolated from each other. It encourages us to think about species as cohesive gene pools, within which there may be substantial variation. It leads to the expectation that we will encounter intermediate situations—populations that are only partially reproductively isolated— and in such situations (e.g., hybridization) it may difficult to decide whether we are dealing with one or two species. The phenetic species concept states that a species is simply a group of organisms that look rather similar (to some unspecified degree). It encounters difficulties when applied to organisms that show sexual dimorphism, polymorphism, different morphologies at different life stages, etc. On the other hand, it may appropriate for asexual organisms where the BSC is inapplicable. 4. Explain the difference between prezygotic and postzygotic isolating factors. Which are thought to be important in allopatric speciation? Under what conditions might selection favor the reinforcement of reproductive isolating factors? Prezygotic isolating factors are those that act to prevent the formation of a zygote
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This note was uploaded on 04/07/2010 for the course BIS 2 taught by Professor Schwartzandkeen during the Fall '09 term at UC Davis.

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BSsqans-lect08 metazophylo&devel - BIS 1B (Winter...

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