Intro/Basics Flashcards
What information do you need in order to describe the structure of a population?
Data (from individuals in a population):
- Sequences
- Genotypes
Can create:
- Parameters (F, S, theta)
- Trees
How can we theorize about the evolutionary forces that shape genetic structure?
Null models (based on theory)
- Gives expected parameter values and tree shapes for neutral case
Test fit of observed data against null model to make inferences
- Fits null expectation - infer action of evolutionary forces
- Deviates from null expectation - infer action of evolutionary forces
What do evolutionary forces do?
Evolutionary forces causes allele frequencies to change
How does mutation affect population genetics?
Mutation creates new genetic variation
What is genetic drift and how does it affect population genetics?
Genetic drift: Random sampling of alleles entering new generation
- Leads to loss of variation over time and divergence of allele frequencies
How does gene flow effect allele frequencies?
Gene flow homogenises allele frequencies among populations
How does selection affect population genetics?
Selection drives changes to allele frequencies relative to fitness differences among genotypes
Give an example of a ‘modifier’ within population genetics
Recombination:
- Reshuffles polymorphisms physically linked on chromosomes, creates new combinations and breaks down associations between linked loci
What important assumptions need to be made about populations within evolutionary genetics?
- Independence among loci
- Random mating among individuals
What is the Hardy-Weinberg equilibrium?
Is a simple null model which gives the neutral expectation for genotype frequencies at a single locus for the observed allele frequencies
- Early 20th century
- p2+2pq+q2 = 1
- p2 and q2 are homozygous, 2pq is heterozygous
- Used as basis for many statistics relating to selection, pop structure and inbreeding
In terms of alleles, what are p and q and what do they sum?
- Proportion of frequency of allele A = p
- Proportion of frequency of allele a = q
- p + q = 1
What assumptions does the Hardy-Weinberg equilibrium make?
- Infinite population
- No mutation
- No migration
- No selection
- Random mating
What are the different selection processes?
- Positive selection
- Purifying selection
- Balancing selection
- Diversifying selection
What are the main different demographic processes?
- Population growth
- Population size fluctuation
- Migration and gene flow
What is the definition of homozygosity?
The proportion of homozygous genotypes (e.g., AA, aa) at a locus in a population
- F = Homozygosity (1-H)
