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Biol 121- 2010.03.24- Evolution- Speciation (Ch. 26).docx

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BIOL 121
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Biol 121 225 Freeman Ch 26Mar 24 10 EvolutionSpeciationWhat is speciation the process by which new species arise it is where biodiversity comes from it is the focus of evolutionary theory How does it occur mutation and genetic drift cause change in allele fq gene flow between populations keeps allele fq constant if gene flow stops the populations will diverge and at some point divergence is significant enough that speciation occurswhen gene flow ends allele fq in the isolated populations are free to diverge and evolve independently if mutation selection and genetic drift cause isolated populations to diverge sufficiently distinct types or species formspeciation Speciation creates evolutionarily large ground finch and medium ground finch are derived from same independent populations eg ground ancestral population finch this ancestral population is split into two populations isolated by the lack of gene flow occupying different islands once the ancestral population splits into separate populations because populations began evolving independently they acquired the distinctive characteristics observed today Barriers that prevent reproduction ie the two main types of barriers that prevent reproduction or prevent gene Prevent gene flow 2 main types flow are prezygotic barriers and postzygotic barriersprezygotic barriers prevent matingfertilization while postzygotic barriers do not prevent matingfertilization but offspring might not be fertile or might not fully develop 1 1 Prezygotic barriers prevent matingfertilization there are three subtypes of prezygotic barriersa Habitat isolation if populations are not in the same place at the same time then there is no opportunity to mate or populations are isolated bc they breed in different habitatsb Behavioural isolation populations do not interbreed because their courtship displays differ eg dances and songs in birds only attract or appeal to mates of one species they are specific to one species onlyc Temporal isolation populations are isolated bc they breed at different times eg Dendrobiumdifferent species of flowers will have pollinators collect pollen on different days eg Bishop pines and Monterey pines release their pollen at different times of the yeard Mechanical isolation matings fail bc male and female genitalia are incompatible 1
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