8.3 gene pools

• what is a population?

  all the organisms of a particular species which live in a habitat
• what do selection pressures do? examples?

  change the allele frequency in the population

  examples of selection pressures:

  • disease
  • competition (for food, mating)
  • environmental conditions (pH, temperature)
• what is a gene pool?

  all the alleles of all genes in a population
• how can selection pressures change the allele frequency in a population?

  via natural selection

  those with an advantageous allele survive an reproduce and pass on allele to offsprings

  so favourable alleles pass on and unfavourable alleles die
• what is stabilising selection?

  • when environmental conditions stay the same
  • favourable characteristics are more common
  • therefore closer to the mean
  • resulting in low diversity

  
• what is disruptive selection?

  when both extremes of characteristics in the normal distribution are made common

  overtime leading to differences in phenotypes and speciation

  
• what is directional selection?

  when the mean characteristics are moved towards one extreme.

  causing a change in the whole population.

  
• what is genetic drift?

  change in allele frequency of population due to chance instead of selection pressures.
• what is population bottleneck?

  when population size rapidly decreases.

  • due to environmental factor (e.g. disease)
  • therefore variety of allele in gene pool decreases
  • and changes in allele frequency
• what is the founder effect?

  • when small amount of individuals in population are isolated
  • form a new population
  • has a limited size gene pool
  • allele frequency wont be reflective of the original population
• under certain conditions, allele frequency shouldn't change from generation to generation
• what is the hardy-weinberg principle?

  allows us to estimate...

  • frequency of alleles in a population
  • if allele frequency changes over time
• what are the assumptions of the hardy-weinberg principle?

  • no mutations - creating new alleles
  • no migration - increasing gene flow in and out of population
  • no selection pressure - alleles equally passed on to next gen
  • random mating
  • large population - genetic drift doesn't eliminate allele
• explain hardy-weinberg equation for genotype frequency?


  frequencies of genotypes must add up to 1

  therefore....

  
• explain hardy-weinberg equation for allele frequency?


  allele frequency must add up to 1

  therefore....

  p + q = 1

  (p = frequency of dominant allele q = frequency of recessive allele)