“Evolutionary speculation constitutes a kind of metascience, which has the same intellectual fascination for some biologists that metaphysical speculation possessed for some mediaeval scholastics. It can be considered a relatively harmless habit, like eating peanuts, unless it assumes the form of an obsession; then it becomes a vice” (Stanier, 1970)
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“Evolutionary speculation constitutes a kind of metascience, which has the same intellectual fascination for some biologists that metaphysical speculation.
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“Evolutionary speculation constitutes a kind of metascience, which has the same intellectual fascination for some biologists that metaphysical speculation possessed for some mediaeval scholastics. It can be considered a relatively harmless habit, like eating peanuts, unless it assumes the form of an obsession; then it becomes a vice” (Stanier, 1970)
Linnaean classification• Two major characteristics
• Kingdom Animalia• Phylum Chordata• Class Mammalia• Order Primates• Family Hominidae• Genus Homo• Species sapiens
BIOL E-127 – 10/01/07
Tree of Life: primary divisions
Tree of Life: primary divisions
Tree of Life: three “domains”• Based on 16S rRNA (Woese, 1987):
Tree of Life: three “domains”• Based on 16S rRNA (Pace, 1997):
Tree basics: meaning
Tree basics: rotation
Tree basics: shape
Tree basics: lengths, unrooted
cladograms vs. phylograms
Tree basics: character change
Key phylogenetic terms
Key phylogenetic terms
Phenetics vs. cladistics
Lysozyme amino acid changes in unrelated ruminants
Phenetics vs. cladistics
Maximum Parsimony• Parsimony – shortest tree (fewest homoplasies)
Molecular phylogenetics• Zuckerkandl & Pauling. 1965. Molecules as documents of
evolutionary history. J Theor Biol. 8:357-366.
• Neutral theory (Motoo Kimura, 1968)
16S rRNA as phylogenetic marker• Why a good molecule?
Process to analyze sequence data
Ortholog vs. paralog?
Good Dataset
[A1, A2, A3, A4] [A1, B2, A3, A4]
Bad Dataset
A B
species 1 species 2 species 3 species 4
A1B1
A2B2 A4
B4A3
B3
1. Collect Sequence DataOrtholog vs. paralog?
2. Sequence Alignment
CGGATAAACCGGATAGACCGCTGATAAACCGGATAC
taxa1taxa2taxa3taxa4
Alignment
3. Choose Models
Ancestral Sequences
Observed Sequences
?Model
Choose “model”
Example: Neighbor Joining (NJ)
4. Choose Methods
Taxa CharactersSpecies A ATGGCTATTCTTATAGTACGSpecies B ATCGCTAGTCTTATATTACASpecies C TTCACTAGACCTGTGGTCCASpecies D TTGACCAGACCTGTGGTCCGSpecies E TTGACCAGTTCTCTAGTTCG
A
B
C
DE
Choose methods: distance-based
A B C D E Species A ---- 4 10 9 8Species B ---- 8 11 10Species C ---- 3 8Species D ---- 5Species E ----
A B C D E Species A ---- 4 10 9 8Species B -19.3 ---- 8 11 10Species C -10 -14.7 ---- 3 8Species D -10.7 -11.3 -16 ---- 5Species E -12.7 -13.3 -12 -14.7 ----
M(AB)=d(AB) -[(r(A) + r(B)]/(N-2)
4. Choose Methods
Maximum Parsimony (MP): Model: Evolution goes through the least number of changes
Maximum Likelihood (ML): L (data| model)
Bayesian Inference
Pr(data)
Pr(model)model)|Pr(datadata)|Pr(model
Markov chain Monte Carlo (MCMC) method for sampling from posterior probability distribution
Discrete character methods
5. Assess Reliability
I. Bootstrap
Re-sampling to produce pseudo-dataset (random weighting)
II. Jacknife
Sampling with replacement
III. Permutation test
Random deletion of sub-dataset
Randomize dataset to build null likelihood distribution
CGATCGTTA
CAATGATAG
CGCTGATAA
CGCTGATCG
taxa1
taxa2
taxa3
taxa4
123456789
Dataset1: 729338554Dataset2: 631981282
…
Dataset1: 1-3-56789Dataset2: 12-45678-
…
10073
Assess reliability
5. Assess ReliabilityExample analysis: ancestry of HIV-1
(Gao et al., 1999)
5. Assess ReliabilityFurther analysis: timing of HIV-1