Lectures 4-7 Flashcards
What is evolutionary genetics
The integration of genetics and evolution. Called the modern synthesis or neo-darwinism
Why was the integration of genetics necessary?
Gave the missing piece to darwins theory as he didn’t know how heredity worked and genetics is the study of heredity.
What causes the variation necessary for natural selection?
Mutation
What does all life evolve around?
Replicating DNA
What is syngamy?
Like fertilisation where two cells fuse/their nuclei fuse.
Missense vs non-sense mutations
Missense is non-synonymous mutations where one amino acid is swapped for another.
Non-sense is the introduction of a premature stop codon
What is a synonymous mutation?
A mutation in which the base sequence changes but not the amino acid sequence
2 tools of evolutionary genetics
- DNA sequencing
2. Mathematical population genetics
What is DNA sequencing
Listing the entire genome and then comparing but can also include comparative karyotyping to give indications of large scale events
Example where comparative karyotyping has been useful
Chromosome 2 of humans appears to be a Robertsonian fusion of two chromosomes when comparing the karyotypes of humans and other apes.
Mathematical population genetics
Genomic data allows for inferences about evolutionary history and answer questions why some salamanders have genomes roughly 40x larger than humans or if we homo sapiens interbred with Neanderthals
What can mathematical modelling be used for
Look backwards in evolution or as a predictive tool
Applications of evolutionary genetics
- Conservation—>plan interventions and preservation
- Agriculture—>GM food and impact
- Engineering—>evolutionary robotics
- Medicine—>disease spread and evolution
Genetic drift
the equivalent of random sampling so chance which individuals survival
- Natural selection is then the bias in this sampling process
Genetic drift always acts
Selection sometimes acts and is based on the relative fitness of the alleles
Expected frequency of B in next generation
p x(Wb/Wtotal)
=(pWb)/(pWb) + (1-p)(Wa)
where p is the frequency of the B allele in parent generation
Wb is the fitness of B allele (the number of copies it will have in the next generation)
ALSO
p +ps/1+ps
Selection coefficient s
This quantifies the strength of selection
1 + s=(Wb/Wa)
If s=0
both alleles have same fitness so neutral mutations and will change due to genetic drift
s<0 so negative
B has lower fitness than A so deleterious mutation
- negative or purifying selection
- if s=-1 then it is a lethal mutation where the presence causes death
s>0 so positive
B has higher fitness so beneficial allele under positive selection (sometimes called Darwinian selection)
Buri 1956
Genetic drift on Drosophila populations using neutral allele
under drift alone and started at 50:50 and then in some one became fixed and in some the other
- vbery few had perfect 50:50 at end of experiment
always 16 individuals
DRIFT has stronger effect in smaller populations
Effective population size = 9 when plotted data against expected from simulations
Effective population
The size of the idealised population that would experience the same amount of genetic drift as the actual population
— almost always smaller as the idealised population has assumption
Idealised populations assumptions
- Hermaphroditic reproduction
- Random Mating
- Constant population size
- No natural selection so allele truely neutral
Effective population size determines the efficacy of selection
as some small populations deleterious mutations can be effectively neutral. And vice versa
Ne x s is small
effective population x selection coefficient
Examples in founder effect and bottle neck