Mitochondrial Point Mutations and Evolution: A Comparative Study

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Mitochondrial Point Mutations and Evolution A
Comparative Study
Plethodon stormi
Plethodon elongatus
Stephanie Weitz Mentor Dr. Dee Denver Department
of Zoology
Plethodon asupak
lthttp//www.californiaherps.com/salamanders/images
gt
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General Background on Western Plethodons

• Important distinction between three species is
  range
• P. elongatus has large range in SW Oregon and NW
  California
• P. stormi is restricted to small pockets in
  Siskiyou mountains of California
• P. asupak is found a few miles west of P. stormi
  in the Siskiyous

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iguresnamei0018-0831-61-2-158-f01gt
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Evolution

• Darwinian Theory
• Species adapt to environment by natural selection

• Neutral Theory of Molecular Evolution
• Introduced by Motoo Kimura in the late 1960s
• At molecular level evolution occurs via random
  drift of neutral mutations
• Foundation of molecular clock hypothesis

http//www.biology-blog.com/images/blogs/12-2007/c
harles-darwin-8221.jpg
http//www.philo5.com/images/VraisPenseurs/KimuraM
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Hypothesis
www.ccc.columbia.edu/Mitochondrial_Diseases/mito/r
ound

• The mitochondrial genomes of these three
  Plethodons have large amounts of non-coding
  sequences that experience faster rates of
  evolution than protein-coding sequences.

Muller et al. 2006
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Objectives

• 1. Compare rates of evolution between three
  species using three different measures
• 2. Use rates to calculate time to the most recent
  common ancestor between species

lthttp//www.californiaherps.com/salamanders/pages/
p.asupak.htmlgt
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Methods
DNA extraction
Designed primers
Obtained tissue samples
PCR-amplify
Perform DNA sequence alignments
MtDNA sequencing
Data analysis in MEGA 4.1 and DNAsp 4.1
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Measuring Rates of Evolution

• Ka rate of substitution at amino acid-changing
  (replacement) codon positions
• Ks rate of substitution at silent codon
  positions
• Knc rate of substitution at any site in
  non-coding regions

http//evolution.berkeley.edu/evosite/evo101/image
s/codon_GCA.gif
http//www.mun.ca/biology/scarr/MGA2-03-28_mtDNA_c
ode.jpg
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Molecular Clock Equation

• TMRCATime to the most recent common
  ancestor (millions of years)
• K Rate of evolution (Ka, Ks, Knc)
• µ Mutation rate (humans.95/base pair/Million
  year)
• Assumptions necessary to use equation

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Data

• Not all primers worked in all species
• P. asupak only half of the primers worked
• Used pairwise DNA sequence alignments to
  calculate Ka, Ks, Knc

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Objective I Results

• Highest rates of evolution occurred at silent
  sites
• Lowest rates of evolution occurred at replacement
  sites
• Rate of evolution intermediate for Knc

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Objective II Results

• Ka and Knc give comparable, more recent times
• P. elongatus and P. stormi are the most closely
  related
• P. stormi and P. asupak are the most distantly
  related

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Conclusion

• Highest rate of evolution occurred at silent
  sites
• P. elongatus and P. stormi are the most closely
  related. P. stormi and P. asupak are the most
  distantly related
• Speciation occurred 250,000 years ago

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Future Research

• Amplify entire mitochondrial genomes for all
  three species
• Find divergence times within species

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Acknowledgements

• Denver lab Dee, Dana, Sam, Caroline, Ashley,
  Bobby, Peter, Larry
• Dr. Kevin Ahern
• HHMI
• Albert Lee, PharmD Candidate 2010
• Dr. Stevan Arnold and Douglas DeGross