Mutations & evolution

• a mutation is a change in the DNA of a cell

  • it can happen in individual genes or in whole chromosomes
• mutations are rare, random changes in genetic material that can be inherited
• only mutations in gametes or cells that divide to form gametes can be passed on to the next generation
• evolution is a change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species
• natural selection is the process by which new species arise from an existing species
• darwin's observations:

  • organisms produce more offspring than are needed to replace them
  • established populations of organisms generally remain the same size
  • members of the same species are not identical as they show variation
• offspring vary in their ability to survive and reproduce
• • mutations occur which provide variation within organisms
  • if the mutation provides a survival advantage the organism is more likely to survive to breeding age = survival of the fittest
  • the mutation will then be passed onto offspring
  • over many generations, the frequency of the mutation will increase within the population until all have the advantage
• darwin's deductions:

  • from observations 1 & 2 he deduced that there is a struggle for existence; many offspring made but population stays the same; therefore there must be a competition for resources & many individuals must die
  • from observation 3 he deduced that if some survive & others die, it must be the organisms who are best adapted to survive to reproduce = survival of the fittest
• within a population there is usually a large amount of genetic variation within the same species

  • this natural variation occurs through small mutations that have occurred throughout time
  • eg different coat colours within the same breed of dog
• natural variation & mutation can sometimes cause one population of a species to become so different they can no longer interbreed to produce fertile offspring

  • this means they have become a new species
  • this process is called speciation
• how does antibiotic resistance develop?

  • high number of bacteria present; few of them are resistant to antibiotics
  • antibiotics enter & kill all bacteria causing illness as well as good bacteria protecting body from infection
  • the resistant bacteria now have preferred conditions to grow & take over
  • bacteria can even transfer their drug-resistance to other bacteria, causing more problems
• bacteria are organisms that reproduce at a very fast rate

  • therefore advantageous genes can become prominent within a population very quickly
• • antibiotic resistance starts when a random mutation gives bacteria resistance to an antibiotic
  • the new resistance bacterium has an advantage when the antibiotic is used
  • the resistance strain will survive & reproduce, passing on the resistance gene to its offspring
  • the resistant strain cannot be killed by the antibiotic & so it is no longer effective in disease control
• How does antibiotic resistance arise?

  • a random genetic mutation causes a bacterium to become resistant to the antibiotic
  • when the antibiotic is used, all the bacteria that do not have the mutation are killed
  • the resistant strain survives & spreads quickly, allowing the population containing just the resistant bacteria to grow
• Bacteria that contain resistant strains are hard to treat & can cause a threat to health