1: Polymorphisms and selection Flashcards
Describe the Out-of-Africa model
- Ancestral pop. in Africa had low consensus size and Ne
- Small subset of this pop. began migrating = Repeated bottlenecks
Define a bottleneck
Rapid reduction in consensus size and genetic diversity between generations
Why do bottlenecks have an effect on pops. ?
- 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
In the Out-of-Africa model, what was the consequences of bottlenecks?
- 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
Define a Synonymous polymorphism
Mutation in protein-coding regions that do not affect amino acid sequence
- Most mutations are probably neutral
- Synonymous diversity, πs
Define a Non-synonymous polymorphism
Mutations in protein-coding regions that change amino acid sequence
- May lead to change in fitness
- Non-synonymous diversity, πA
Non-synonymous diversity should be ____ than synonymous diversity
higher
Smaller Ne leads to ____ selection
weakend
Describe will happen to deleterious mutations in a population with small Ne
- Small Ne = weakened selection
- Leads to deleterious mutations drifting to high frequencies or even fixation
Describe will happen to beneficial mutations in a population with small Ne
- Small Ne = weakend selection
- Leads to increased chance of stochastic loss of beneficial mutations
Describe the faster X effect
→ 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
How does the faster X effect affect speciation?
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
