Lec 4
Sunday, January 19, 2020
6:35 PM
How does one prove homology?
- Similarity due to common ancestry
- Using sequence can help with common ancestry
- Similar sequences suggest they have the same function
- Sequence does not have to be identical in homology
2 Algorithms to attack Alignment
- High alignment suggest functional similarity and common ancestry
○ Want to align to see how similar they are
○ Global Alignment
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○ Local Alignment looks for any regions with similarity. Not attempting to align end t
similarity
○ Local Alignment is a lot faster than global
Synonymous and Non-Synonymous Alignment
Synonymous=Silent Differences
○ Local Alignment is a lot faster than global
Synonymous and Non-Synonymous Alignment
Synonymous=Silent Differences
Non-Synonymous=Changes amino acid sequence
Establishing homology through probability
- The higher the similarity between two sequences the lower the probability that
they originated independently of each other and became similar just by chance
- E Value (BLAST Statistic)
○ Chance that two sequences have the score simply by chance
○ E<0.00001=homologues! (Anything below 10 to the mines 5 is deemed
homologous