1: Polymorphisms and selection

Question 1

Describe the Out-of-Africa model

Answer 1

1. Ancestral pop. in Africa had low consensus size and Ne
2. Small subset of this pop. began migrating = Repeated bottlenecks

Question 2

Define a bottleneck

Answer 2

Rapid reduction in consensus size and genetic diversity between generations

Question 3

Why do bottlenecks have an effect on pops. ?

Answer 3

• Initial sampling effect reduces standing genetic variation
• Loss of variability due to genetic drift is more rapid in smaller pops.
• Variation increase from mutations takes time to accumulate

Question 4

In the Out-of-Africa model, what was the consequences of bottlenecks?

Answer 4

• Non-African pops. Should have lower π (and Ne)
• Each new habitat was probably colonised by a small founding pop.
  so… pop.s that reside further away from Africa should have lower diversity

Question 5

Define a Synonymous polymorphism

Answer 5

Mutation in protein-coding regions that do not affect amino acid sequence
- Most mutations are probably neutral
- Synonymous diversity, πs

Question 6

Define a Non-synonymous polymorphism

Answer 6

Mutations in protein-coding regions that change amino acid sequence
- May lead to change in fitness
- Non-synonymous diversity, πA

Question 7

Non-synonymous diversity should be ____ than synonymous diversity

Answer 7

higher

Question 8

Smaller Ne leads to ____ selection

Answer 8

weakend

Question 9

Describe will happen to deleterious mutations in a population with small Ne

Answer 9

• Small Ne = weakened selection
• Leads to deleterious mutations drifting to high frequencies or even fixation

Question 10

Describe will happen to beneficial mutations in a population with small Ne

Answer 10

• Small Ne = weakend selection
• Leads to increased chance of stochastic loss of beneficial mutations

Question 11

Describe the faster X effect

Answer 11

→ The X chromosome evolves faster than the rest of the genome due to purifying selection being weaker
= More weakly deleterious mutations becoming fixed compared to autosomes

Question 12

How does the faster X effect affect speciation?

Answer 12

Pops. are separated and come together and are unable to breed due to genetic incompatibility → likely due to the X evolving faster than the autosomes