Molecular Evolution II Flashcards
Describe selective sweeps
- sweeps of beneficial mutations
- seen in haemagglutinin (HA) gene of human influenza virus
- fixation of new amino acids allow the virus to escape host antibodies
Give an example of parallel adaptation (convergent evolution)
monarch butterfly, red milkweed beetle, oleander aphid and large milkweed beetle all adapted to milkweed consumption
Describe ‘synonymous’ mutations
- do not change protein
- likely to be neutral
Describe ‘non-synonymous’ mutations
- change protein
- may be neutral, deleterious or beneficial
What happens if we compare rates of evolution at synonymous and non- synonymous sites
- rate of non-synonymous substitutions: dN
- rate of synonymous substitutions: dS
- no selection: dN/dS = 1
- purifying selection: dN/dS < 1
- positive selection: dN/dS > 1
Compare D. yakba with D. simulans
- 6 million years divergence
- 45% of non-synonymous differences due to positive selection
- 270,000 selected differences
- 1 selective sweep every 45 years
Neutrality gives us
an important null hypothesis – what would genetic variation look like without selection
Define innovation
new traits that allow organisms to exploit their environment in new ways
Give some innovations
- C4 photosynthesis
- multicellularity in Volovox algae
How to explain the origin of complex traits?
gene acquisition
Describe enzyme ‘promiscuity’
- mutations to existing genes coding for enzymes can create new enzymatic phenotypes with new enzymatic functions
- primary ligands convert to promiscuous ligands
Describe HGT in prokaryotes
- common in bacteria
- 90% genes in some bacterial genomes derived from HGT
- ‘en bloc’ transfer of biological functions
Plasmids
- semi-autonomous DNA molecules that can pass between bacteria
- genes can be incorporated into chromosome
Explain one pathway for antibiotic resistance
environmental bacteria give resistance to gut plasmids that pass to human pathogens
Where do new genes come from?
gene duplication
