Molecular Evolution II

Question 1

Describe selective sweeps

Answer 1

• 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

Question 2

Give an example of parallel adaptation (convergent evolution)

Answer 2

monarch butterfly, red milkweed beetle, oleander aphid and large milkweed beetle all adapted to milkweed consumption

Question 3

Describe ‘synonymous’ mutations

Answer 3

• do not change protein
• likely to be neutral

Question 4

Describe ‘non-synonymous’ mutations

Answer 4

• change protein
• may be neutral, deleterious or beneficial

Question 5

What happens if we compare rates of evolution at synonymous and non- synonymous sites

Answer 5

• 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

Question 6

Compare D. yakba with D. simulans

Answer 6

• 6 million years divergence
• 45% of non-synonymous differences due to positive selection
• 270,000 selected differences
• 1 selective sweep every 45 years

Question 7

Neutrality gives us

Answer 7

an important null hypothesis – what would genetic variation look like without selection

Question 8

Define innovation

Answer 8

new traits that allow organisms to exploit their environment in new ways

Question 9

Give some innovations

Answer 9

• C4 photosynthesis
• multicellularity in Volovox algae

Question 10

How to explain the origin of complex traits?

Answer 10

gene acquisition

Question 11

Describe enzyme ‘promiscuity’

Answer 11

• mutations to existing genes coding for enzymes can create new enzymatic phenotypes with new enzymatic functions
• primary ligands convert to promiscuous ligands

Question 12

Describe HGT in prokaryotes

Answer 12

• common in bacteria
• 90% genes in some bacterial genomes derived from HGT
• ‘en bloc’ transfer of biological functions

Question 13

Plasmids

Answer 13

• semi-autonomous DNA molecules that can pass between bacteria
• genes can be incorporated into chromosome

Question 14

Explain one pathway for antibiotic resistance

Answer 14

environmental bacteria give resistance to gut plasmids that pass to human pathogens

Question 15

Where do new genes come from?

Answer 15

gene duplication

Question 16

Describe gene duplication

Answer 16

• duplication events occur at high rate
• most duplicates are inactivated due to mutation