Biology 1002B Study Guide - Final Guide: Asymmetric Cell Division, Volvox, Point Mutation

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19 Apr 2017
Cycle 11: Molecular Evolutio
GIsA gene from Volvox vs Chlamydomonas
Homology: similarity due to common ancestry
o Should have the same underlying genes
o Does not mean they have the same function
GIsA Gene:
o In Volvox has a function (asymmetric cell division)
Volvox has small somatic cells and large reproductive cells
Volvox may have recruited this gene
o In Chlamy no known function (you can knockout the gene and Chlamy will be fine)
o If ou hae a kokout i Volo, ou a iset Chla’s gee ad it will still function correctly
Reasons why one does sequence alignments
Sequence alignments: attempts to match up the bases of 2 gene sequences or the amino acids of 2
o We can infer a lot from similarity (e.g. similar evolutionary origin)
Differences between global vs local
Global: take both sequences and match as many bases
possible in the entire sequence
o If you have 2 sequences pretty close to the same
length and similar (closely related species)
Local: look for little regions of high similarity
o Faster
Relationship between E-value and likelihood of homology
E-value: probability that the 2 sequences have the same score simply by chance
o If E < 10-5 then the sequences are homologous
Synonymous vs non-synonymous mutations
Synonymous mutation: point mutation that does not alter amino acid sequence
o Like a so, utated odo has the sae eaig as the oigial odo
o Protein is not affected, no role in evolution
Non-synonymous mutation: usually an insertion/deletion, but can also be a point mutation that alters
the amino acid sequence
o Changes the protein in some way
o Insertion/deletion causes frame shifts -> usuall lethal ad potei does’t futio
o Point mutations change one amino acid -> protein may be viable
Point mutations may code for premature stop codons -> probably lethal
o May be advantageous and is subject to natural selection
o Increases diversity in the gene pool and drives evolution on a micro-evolutionary level
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