Lecture 21 - Lecture 22: Feb. 22 Species & Speciation...

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1 Lecture 22: Feb. 22 What are Species? Reproductive Barriers -pre zygotic: behavioral, spatial, temporal, mechanical & gametic - post zygotic: hybrid sterility & inviability How Do Species Form? Allopatric Speciation - initial barrier to gene flow is geographic - process and examples Sympatric Speciation - initial barrier to gene flow is biological: polyploidy, host shift, changes in mate preferences - hybrid speciation Discussion Activity next Week Article on link between (week 9 folder) Complete essay due today Exam 2: Monday, March 3 Covers lectures 12-22 Optional Review Session on Sun., March 2, 7 to 9pm, Nat. Sci. Aud. Check Qwizdom Points on SAMS https://cats.lsa.umich.edu/ Chapter 25 : 538-553 Biology in the News The Biological Species Concept (Ernst Mayr) Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other groups. Ernst Mayr at 94 Sturnella magna Sturnella neglecta meadowlarks distinct songs adv.: widely used by biologists proponents say species are real biological entities - reproductive isolation means evolutionary independence dis.: can’t apply to extinct species can’t apply to asexual organisms even for living, sexual species may be difficult to apply in the field Biological Species Concept (BSC)
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2 Reproductive Barriers Separating Species A. Pre zygotic – prevent fertilization; no hybrid zygotes form B. Post zygotic - fertilization occurs & hybrid zygote forms, but hybrid fails to
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Lecture 21 - Lecture 22: Feb. 22 Species & Speciation...

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