Population Genetics Of Adaptation I Flashcards
How does speciation come about?
Over time, natural selection results in populations becoming divergently adapted to different environment
An example of speciation
Adaptive radiation (Darwin’s finches)
What is natural selection?
The mechanism of evolution change in populations
What did Mendel demonstrate?
Particulate inheritance
What is a gene?
Unit of heritable material
What is an allele?
Discrète variant state of a gene
What is the Hardy-Weinberg Theorem?
A conceptual model of organisation of genetic variation
What are the assumptions of the Hardy-Weinberg theorem?
- infinite population size
- random mating
- no difference in viability
What is the multiplication rule?
The probability of two independent events both occurring is the product of the probability of each event occurring
What is the addition rule?
The probability of any one of a set of mutually exclusive events occurring is the sum of the probabilities of the individual events
Neutral modelling
Looking for what patterns we might expect when nothing interesting is going on
What is genetic drift?
Stochastic changes in allele frequency due to chance
What fundamental truth does drift rely on?
Populations are not infinite
What does drift lead to?
- Stochastic changes in allele frequencies
- loss of genetic variation
What is the relationship between drift strength and population size
As population size increases, strength of drift decr were
Graphs demonstrating drift relationship to population size
- plotting allele frequency against number of generations
- as n increases, allele frequency maintains a more central position across generations - remains more constant
Allele frequency as a measure of
Genetic variation
Which allele frequency would indicate the highest genetic variation?
0.5
Selection acts on
Phenotypes
What does selection acting upon phenotypes result in
Changes in allele frequency
W
Fitness
Fitness definition (Hardy-Weinberg)
Relative reproductive rate of individual with a given genotype
Selection coefficient
- s
- change in fitness associated with allele when homozygous
If s>0, the allele is
Beneficial
Is s<0, the allele is
Deleterious
Dominance
- h
- the extent to which the effect of an allele on fitness is masked when heterozygous
When h=1
The allele is dominant
When h=0
The allele is recessive
What does change in allele frequency depend on?
- fitness of each genotype
- average population fitness
Why does dominance accelerate adaptation?
- rare mutations are almost never homozygous because of larger selective coefficients
- dominance is rare
Migration rate
- m
- probability that allele foot arrives on island by migration
P*
Average allele frequency on other islands
Give the equation for the island model of structured populations
P2 = P1(1-m)+P*(m)
What does migration prevent?
Divergence between populations
Migration is essentially the phenotypic level of what genotypic process (my thoughts)
Gene flow
If there is gene flow amoung populations,
They will all eventually reach the overall average allele frequency
Relationship between gene flow and allele frequency
Plotting allele frequency (p), against number of generations, if gene flow (migration) is present, equilibrium frequency of 0.5 (p with a flat cap) will be reached after 42 generations
How do migration, selection, and genetic drift affect genetic diversity?
Migration: increases diversity
Selection: deterministic loss of low fitness allele
Drift: stochastic loss of diversity by chance
Genetic diversity
Provides the ‘fuel’ for adaption by natural selection
Selective sweeps happen faster for allleles that are
- Codominant
- h = 0.5
Migration
Homogenises allele frequencies, while bringing genetic diversity back into populations
Gene drift leads to the loss of
Rare alleles
