Population genetics Flashcards
define evolution:
- change of allele frequencies over time
what causes change to allele frequencies:
- natural selection
- genetic drift
natural selection:
- organisms best suited to environment have more resources for survival and reproduction
fitness:
- relative genetic contribution of individual to next generation
- successful alleles individuals carry passed on
adaptation:
- change in populations through natural selection
directional selection:
- individuals with traits at one extreme favoured over another
stabilising selection:
- individual with intermediate traits favoured
disruptive selection:
- individuals from either extreme favoured
eg. directional selection
- herbicide application
- many plant species evolving with resistance
- also antibiotic resistance in hopsitals
genetic drift:
- change in allele frequencies across generations due to chance events
list chance events:
- random disturbances
- small populations
- Founder effects
population size:
- genetic drift more likely to occur in small populations
= fixation of allele and loss of others - less likely in large populations, random events are buffered
Founder effect:
- individuals disperse to new area, subset of alleles from entire population
- large change in allele frequencies
- inbreeding
bottleneck effect:
- rapid decrease in population size due to disturbance or natural disaster
- removes individuals with some alleles from population
- those which survive alter gene frequencies
eg. Pingelap
- island of colourblind
- 10% individuals completely colourblind in population
- 1775 population reduced to 20 people due to typhoon
- bottleneck effect
- all colourblind people can be traced back to one person with recessive genetic disorder
significance of Pingelap:
- random disturbance initially changed allele frequencies
- bottleneck left small founding population
- random chance + small population size + inbreeding = allele not adaptive have high frequency in population
gene flow:
- allele moves btw populations
- can increase genetic variation
- decrease effects of genetic drift
- can lead to homogenisation across populations
- dilute effects of localised natural selection and adaptation
population:
- individuals of species which interbreed with each other but not w individuals of same species of another population
- different populations becomes more genetically differentiated
- over long periods of time, no genetic exchange will evolve into different species
gene pool:
- entire genetic content of population
- every allele
- we only study specific alleles
mutations:
- change in DNA sequence
- error in DNA replication
- caused by mutagens
- most mutations are deleterious, but some create alleles that increase fitness
sexual reproduction:
- new combinations of alleles produced
- recombination of alleles in meiosis
Hardy-Weinberg equilibrium:
- when allele and genotype frequencies remain constant from gen to gen, population is not evolving
- only Mendelian segregation and recombination of alleles at work
- this type of population: Hardy-Weinberg equilibrium
how to determine offsprings in Hardy-Weinberg equilibrium:
- consider combo of alleles in all crosses in population (genotype and allele frequencies)
- will add up to 1 (100%)
Hardy-Weinburg equilibrium: equation
- at locus with 2 alleles
- 3 genotypes will appear:
p2 + 2pq + q2 = 1
result of not meeting 1 of 5 conditions of Hardy-Weinberg equilibrium:
- no mutations
- random mating
- no natural selection
- extremely large population size
- no gene flow
- allele and genotype frequency will change
- real populations change over time
evolution:
- change in allele frequencies btw generations
to calculate genotype frequency:
no. of individuals with specific genotype ÷ no. of total individuals
to calculate allele frequency:
no. of particular allele ÷ total no. of alleles in all individuals
how many genotypes per individual?
one
how many alleles per individual?
two
- one per chromosome of every individual
