03/13/06
From Biol301
Phylogenetic Thinking
- What phylogenetic trees don't tell us
- Which species is ancestral to another
- Which species are advanced or primitive
- Which species are older or younger
- Family Trees
- Women can follow mitochondrial DNA (mDNA) to track their ancestry.
- Men can follow Y chromosome
- Phylogenies tell us about evolutionary cousins
Molecular Systematics
- 90%+ of trees in 2006 are DNA-based.
- Ribosomal RNA (rRNA) is used for long-distance relation building because it mutates very slowly.
- Speed of mutation from slowest to fastests: rRNA / regular DNA / mDNA
- Advantages of using DNA to build trees.
- Not subjective
- Discrete character states
- Present in all species (and present at all times, unlike plummage, etc.)
- Morphology is subject to convergence but neutral mutations are not.
- Neutral Mutations occur at a fairly regular rate
- we can use this rate as a clock
- about 6 million years ago humans and chimps split
- use a known geological event to calibrate the clock (i.e. the formation of the Isthmus of Panama)
- Sequence from Atlantic vs. Pacific seastar are 3.5% different. So 1% change over each of 3.5 million years. Then if we find Carribean vs. Meditteranean seastars are 10% different, we can infer a 10 million-year-ago divergence.
