genetic diversity & adaptations

• random mutations cause formation of new alleles
• meiosis recombines different alleles creating unique gametes
• sexual reproduction mixes alleles to creates genetically unique individuals
• what is genetic diversity?

  the number of different alleles for a particular gene present within a species
• what is a gene pool?

  the number of different alleles for a gene
• members of the same species have the same genes but different combinations of alleles
• how is genetic diversity increased in a population?

  1. random mutation
  2. gene flow
• what is gene flow?

  different alleles are introduced by individuals joining a population and successfully breeding
• gene pools:

  • if there is higher genetic diversity in the population
  • then gene pool is larger
  • as there are more different alleles
• allele frequency can change due to random chance
• genetic drift:

  • in smaller populations random changes are significant in changing allele frequency
  • can lead to evolutionary changes
• how is genetic diversity decreased in a population?

  • genetic bottlenecks
  • e.g the founder effect
• genetic bottlenecks:

  • population is reduced due to natural catastrophe
  • only a few survivors with a small range of alleles between them
  • population size increase again
  • but with a reduced number of different alleles (lower genetic diversity)
• the founder effect:

  • small number of individuals colonise a new habitat
  • and start a new population
  • new population has a small range of different alleles between them (lower genetic diversity)
• what is a population?

  a group of individuals of the same species that can interbreed
• natural selection process:

  1. genetic variation exists in the population
  2. as there are different alleles in the gene pool
  3. there is intraspecific competition for resources
  4. individuals that have a selective advantage (possess advantageous alleles)
  5. are better adapted to the environment
  6. they are more likely to survive and reproduce
  7. passing on their advantageous alleles
  8. this increases the allele frequency
• what is evolution?

  the gradual change in species over time
• certain characteristics are selected for (e.g bacteria resistance)
• what is selective pressure?

  an environmental factor that influences which individuals within a population are more likely to survive and reproduce e.g pesticide on plants
• directional selection:

  • occurs in a changing environment eg climate change
  • selects for one extreme phenotype
  • reduces variation (increased standard deviation)
  • increase in frequency of advantageous alleles
  • so an increasing number of population becomes well adapted to environment
• stabilising selection:

  • occurs in a unchanging environment
  • selects against extreme phenotypes (selects for mean)
  • reduces variation
  • increase in frequency of advantageous alleles
  • so increasing number of population becomes well adapted to environment