Population Genetics And Natural Selection Flashcards
Population
Localised group of individuals of the same species
Gene pool
Total aggregate of genes (and their alleles) in the population at one time
Why do you need to estimate the frequencies of genotypes in a population
- To predict how many individuals will inherit a disease
- To estimate the proportion of individuals who are ‘carriers’ of a genetic disease
How do we predict genotypes in a population?
Hardy-weinberg equation
Hardy - weinberg equation
Allele frequency:
P + q = 1
(P - frequency of dominant allele. Q - frequency of recessive allele)
Genotypic frequency:
P^2 + 2pq + q^2 = 1
Allele frequencies can change via…
- non random mating
- assertive mating
- inbreeding
- random genetic drift
- bottleneck effect
- founder effect
- natural selection
- gene floe or migration
- mutation
Random genetic drift
- a random change in allele frequencies due to sampling error over generations
- happens quickly in small populations
- reduces diversity??
Bottle neck effect
- original population has a pool of allele frequencies
- a population reduction of brittle neck effect results in alleles being lost for ever, regardless of the population growing quickly again
Founder effect
When migration to new place means the new population does not repsrent all the alleles in origanial population
Stabilising selection:
Reduces variation but doesn’t change the mean of phenotypes favoured by natural selection
- peak gets higher and narrower
Directional selection:
One extreme is favoured and the peak shorts in one direction
- changes the mean value towards one exrtreme
Disruptive selection
- two extremes are favoured, producing two peaks
Spatial distribution of genetic variation
The gradual geographic change in genetic/ phenotypic composition is called a CLINE
