Drift and selection

• evolution


  the change over time in the proportion of individuals in a population differing in one or more inherited traits
• Natural selection


  the increasing frequency of favoured phenotypes as a result of differential reproductive success in a population.
• gene pool


  the total number of genes of every individual in an interbreeding population
• Directional selection


  shifts the genetic make up of the population by favouring one extreme over others as a result of the environmental change.
• diversifying selection


  favours phenotypes of opposite extremes over intermediate phenotypes
• Stabilising selection


  Removes extreme variant phenotypes from population, favours intermediate phenotypes

  Reduction in variation and maintenance of existing phenotypes.
• genetic drift


  the changes seen in the alleles in the population due to loss of individuals or lack of reproduction of particular individuals
• Genetic bottlenecks can occur when populations are reduced in size because of natural disasters such as volcanic eruptions, earthquakes, hurricanes etc.
• Founder effect occurs when small groups split off from larger group and establish new colony with limited gene pool
• gene flow is the gain or loss of alleles from a population by the movement of individuals or gametes into or out of a population
• the Hardy-Weinberg principle


  in the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over generations.

  Can be used to determine whether a change in allele frequency is occurring over time as changes suggest evolution is occurring
• conditions of the hardy weinberg equilibrium?

  • No natural selection
  • Random mating
  • No mutation
  • Extremely large population size
  • No gene flow
• p^2+2pq=q^2=1

  where;

  p^2=Frequency of homozygous dominant genotype

  q^2= frequency of the homozygous recessive genotype

  2pq=frequency of heterozygous genotype
• absolute fitness


  the ration between the frequency of individuals of a particular genotype after selection, to those before selection
• Relative fitness

  the ratio of surviving offspring per individual of one genotype compared to the number of surviving offspring per individual of the most successful genotype
• sexual selection


  the non-random process involving the selection of alleles that increase the individuals chances of mating and producing offspring
• sexual selection causes


  male-male rivalry and female choice
• sexual dimorphism


  distinct differences in size, ornamentation or colouring
• fitness


  is an indication of an individuals ability to be successful at surviving and reproducing. it refers to the contribution made to the gene pool of the next generation by individual genotypes and can be defined in relative or absolute terms.
• Co-evolution


  the process by which two or more species evolve in response to selection pressures imposed by each other
• selection pressure


  a change in traits of one species which affect the other species
• mutualism


  a type of symbiotic interaction in which both species benefit by the association
• parasitism


  a type of symbiotic interaction where 1 species is benefited by the association and the other is harmed
• commensalism


  a type of symbiotic interaction where 1 species benefits from the association whilst the other is neither harmed nor benefited
• The red queen hypothesis

  in a co-evolutionary relationship, a change in traits of one species can act as a selection pressure on the other species. This means that species in these relationships must adapt to avoid extinction.