Cladistics (5.4)
SECTION LINKS: |
Evolution/ Natural Selection/ Cladistics Notes (includes 5.1, 5.2, 5.4, & HL 10.3)
HL Extension: Topic 10.3 |
Cladistics
Cladistics: a hypothesizing classification method of animals and plants that groups organsisms according to the number of measurable characteristics that they have in common.
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Clades
Clade: a group of organisms that evolved from a common ancestor
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Cladograms
Cladogram: a tree diagram that indicates the most probable sequence of divergence in clades
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A and D are similarly diagramed. However:
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B and C are similarly diagramed
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While all are very similar the indication is in which species or organsim is older and which is more likely to share a closer common ancestor to the lizard.
Molecular Clocks
The DNA sequence differences that accumulate between two organsims for a particular gene or DNA sequence can be determined.
Assumptions:
Molecular Clock: "the average rate at which a species' genome accumulates mutations, used to measure their evolutionary divergence and in other calculations." (google dictionary) What is a Molecular Clock? (simple and easy) Molecular Clocks and Estimating Species Divergence DNA homology- sequencing (flash animation-very detailed) |
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However, there are some problems with using DNA to track divergence.
- Half life of DNA is ~520 years, which means that for really old organsisms DNA does not or should not exist
- Due to #1, it makes it impossible to track changes over the course of billions of years (or through observable science)-- so we lean on historical science
- While we observe known mutational changes in DNA within a given time period, these are assumed to stay exactly the same and never change- which is a big assumption with 7 million years to play with.
Reclassifying Clades
Until recently 275 genera were classified as apart of the figwort family
Reclassification of Figworts (news article) |
Gene BLASTing
We can compare genes through various different methods. Because of sequencing methods we have now sequenced genomes of many different organisms. So we are compare genes of different organism.
Gene Idenification Database- OMIM gene search Gene/ Protein blast comparison - NCBI blast technology Sequence search - NCBI Sequence search Genes researched:
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Directions
For Student work: See the following document |