Class Notes (839,590)
United States (326,038)
01:119:115 (825)
D'arville (38)
Lecture

Ch. 20

3 Pages
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Department
Biological Sciences
Course Code
01:119:115
Professor
D'arville

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CH. 20 Speciation and Macroevolution  Species concept o  Morphological species concept    Limitations: polymorphism, one species can have different  structures.  • They may be within the same species, but they have  different structures o  Biological species concept:  species are populations that are reproductively  isolated in nature and produce fertile viable offspring  Limitations: relevant only for sexual organisms  Under artificial conditions, species may interbreed  Reproductive isolation o How a species stays a species o Barriers to gene flow   Postzygotic  •  Hybrid inviability  spontaneous abortion. Zygote forms but  not correctly, wont mature into an adult •  Hybrid sterili y o Viable, not fertile o Mule and horse o Tiger and lion •  Hybrid zones : two closely related species in the process of  diverging.  When they mix, they create fertile hybrids with  low fitness o Very rare o Reproductive barriers developed due to low fitness   Prezygotic­  before fertilization •  Behavioral isolatio : due to behavior isolation o No fertilization or mating o Male cannot make a mistake, must show his quality  o Species distinguish other species based on signals o Signals facilitation species­specific recognition  Auditory­ crickets  Chemical­ mosquito  Visual­ firefly •  Temporal isolation:  seasonal mating •  Mechanical isolation  anatomical incompatibility o “Lock and key” reproductive parts must fit together o puppy will try to reproduce with a rabbit •  Habitat isolati n •  Gametic isolation  biochemical incompatibility  o Egg and sperm will not recognize each other  Speciation: interruption of gene flow due to geographical elements  o  Allopatric ­ species in two different locations.  Geographical isolation of  populations  Gene flow is interrupted because migration is inhibited  Most speciation is allopatric  Physical barrier arises separating a population  Barrier prevents gene flow between the two populations  Genetic differences accumulate  Different selections pressures  Ex: gene flow interrupted by mountains.  Now two populations.   New alleles are developed that may be beneficial that will wipe out 
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