BIOL 112 Lecture 12
Jump to navigation
Jump to search
« previous | Monday, September 24, 2012 | next »
Building Trees using Molecular Data
Finding orthologs:
- Take a query sequence (ortholog of 1 species)
- Blast it against genome database (comparing similarities)
- Results ranked best to worst (ranked by percent identity[1])
Constructing Phylogenies
Distinguish homology vs. analogy
- Are there other points of similarity? If two species share a common ancestor, then they should have many points of similarity (high % identity)
- Analogy results in few points of similarity and many differences (low % identity)
Genomes and Evolutionary History
Homologous genes between species (orthologs) originate from a common ancestral gene.
Differences in orthologs and studying duplicated paralogs give clues to how genome changes lead to different forms.
For example: Evolution of jawed fish
- Invertebrate had no backbone and no jaw bone
- 1st duplication 520 mya led to a backbone but no jawbone
- 2nd duplication 420 mya led to a backbone and a jawbone
Evolution of Eukaryotes
Eukaryotes are unique (compared to prokaryotes) because they can contain mitochondria and chloroplasts. Both mitochondria and chloroplasts have:
- circular DNA genomes (like bacteria)
- are closely related to bacterial genes (orthologs)
- Have separate membranes similar to bacterial cells
"horizontal transfer" [2] between bacteria and primitive eukaryotes gave rise to mitochondria and chloroplasts:
Endosymbiosis of Prokaryotes
- Aerobic prokaryote was engulfed by primitive eukaryote to form mitochondria
- Photosynthetic prokaryote (probably cyanobacteria) was engulfed by primitive eukaryote to form chloroplasts