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Evolution at the DNA level

Short Primer on Comparative Genomics Today: Special guest lecture 12pm, Alway M108 Comparative genomics of animals and plants Adam Siepel Assistant Professor of Biological Statistics and Computational Biology Cornell University. Evolution at the DNA level. Deletion. Mutation.

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Evolution at the DNA level

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  1. Short Primer on Comparative GenomicsToday: Special guest lecture12pm, Alway M108Comparative genomics of animals and plantsAdam SiepelAssistant Professor of Biological Statistics and Computational Biology Cornell University

  2. Evolution at the DNA level Deletion Mutation …ACGGTGCAGTTACCA… SEQUENCE EDITS …AC----CAGTCCACCA… REARRANGEMENTS Inversion Translocation Duplication

  3. Orthology and Paralogy Yeast Orthologs:Derived by speciation Paralogs: Everything else HA1 Human HA2 Human WA Worm HB Human WB Worm

  4. Orthology, Paralogy, Inparalogs, Outparalogs

  5. Synteny maps Comparison of human and mouse

  6. Synteny maps

  7. Building synteny maps Recommended local aligners • BLASTZ • Most accurate, especially for genes • Chains local alignments • WU-BLAST • Good tradeoff of efficiency/sensitivity • Best command-line options • BLAT • Fast, less sensitive • Good for • comparing very similar sequences • finding rough homology map

  8. Index-based local alignment …… Dictionary: All words of length k (~10) Alignment initiated between words of alignment score  T (typically T = k) Alignment: Ungapped extensions until score below statistical threshold Output: All local alignments with score > statistical threshold query …… scan DB query Question: Using an idea from overlap detection, better way to find all local alignments between two genomes?

  9. Local Alignments

  10. After chaining

  11. Chaining local alignments • Find local alignments • Chain -O(NlogN) L.I.S. • Restricted DP

  12. Progressive Alignment x • When evolutionary tree is known: • Align closest first, in the order of the tree • In each step, align two sequences x, y, or profiles px, py, to generate a new alignment with associated profile presult Weighted version: • Tree edges have weights, proportional to the divergence in that edge • New profile is a weighted average of two old profiles y z w

  13. Threaded Blockset Aligner HMR – CD Restricted Area Profile Alignment Human–Cow

  14. Reconstructing the Ancestral Mammalian Genome Human: C C Baboon: C G Dog: G C or G Cat: C

  15. Neutral Substitution Rates

  16. Finding Conserved Elements (1) • Binomial method • 25-bp window in the human genome • Binomial distribution of k matches in N bases given the neutral probability of substitution

  17. Finding Conserved Elements (2) A C • Parsimony Method • Count minimum # of mutations explaining each column • Assign a probability to this parsimony score given neutral model • Multiply probabilities across 25-bp window of human genome A A G

  18. Finding Conserved Elements

  19. Finding Conserved Elements (3) GERP

  20. Phylo HMMs HMM Phylogenetic Tree Model Phylo HMM

  21. Finding Conserved Elements (3)

  22. How do the methods agree/disagree?

  23. Statistical Power to Detect Constraint N L C: cutoff # mutations D: neutral mutation rate : constraint mutation rate relative to neutral

  24. Statistical Power to Detect Constraint N L C: cutoff # mutations D: neutral mutation rate : constraint mutation rate relative to neutral

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