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pull of recent
sampling bias, as fossil record gets older its harder to obtain fossils from later years, whereas fossils that arent as old are easier to find
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rarefaction
- normalized samples to avoid biasing species richness
- extinction rate- over time decreases without looking at mass extinction
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end of permian
- largest extinction, volcanic eruptions, global acid rain
- 251 MYA
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end of ordovician
- 439 MYA second largest
- possibly due to global warming
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end of cretaceous
- 65 MYA K/T boundary
- large asteroid with changes in environment
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todays extinction
loss of habitat, exotic predators
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overharvesting
population crash which eventually causes extinction
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extinction of trilobites
dead clade walking, some lineages diverge but then die off
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stochiastic
mutations are random, probability 0 or 1, cat predict which gene copy will mutate
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not adaptively directed
whether a gene will increase the fitness does not affect whether a mutation will occur
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base pair rate of mutation
mutation per generation
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locus mutation rate
mutations on a much larger scale than base pairs
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nondisjunction
at meiosis can lead to reduced or unreduced gametes
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aneuploidy
n +1 reduced gametes
-
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polyploid
fusion of unreduced gametes
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autopolyploid
fusion of unreduced gametes from the same species
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allopolyploid
fusion of gametes from different species
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translocation
transfer of a segment to another nonhomologous chromosome
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fusion
two homologous chromosomes become 1 can lead to balanced euploid species and start new species
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