genetics and evolution

• evolution

  • Charles Darwin proposed the theory of evolution after years of studying fossils
  • individual organisms within a particular species show a wide range of variation for a characteristic
  • individuals with the characteristic most suited to the environment are more likely to survive to breed successfully
  • the characteristics that have enabled these individuals to survive then passed onto the next generation
• issues with Darwins evolution theory

  • challenged the idea that god made all the animals and plants that live on earth
  • there was insufficient evidence at the time the theory was published to convince many scientists
  • the mechanism of inheritance and variation was not known until 50 years after the theory was published
• jean baptiste Lamarck

  • believed that changes occur in an organism during its lifetime
  • vast majority of cases, this type of inheritance cannot occur
• alfred russel Wallace

  • proposed the theory of evolution by natural selection and published joint writings with Darwin which prompted Darwin to publish the origin of species the following year
  • Wallace worked on warning coloration in animals and his theory of speciation
• mendel

  • in the mid 19th century, Gregor Mendel carried out breeding experiments on plants. one of his observations was that the inheritance of each characteristic is determined by units that are passed onto descendants unchanged
• mendel timeline

  • in the late 19th century, behaviour of chromosomes was observed during cell division
  • early 20th century - was observed that chromosomes and mendels units behaved in similar ways. units were now called genes
  • mid 20th century - structure of DNA was determined and gene function was worked out
  • gene theory developed
• what is speciation?

  • a species is a group of individuals that have similar characteristics (alleles/DNA) that are capable of interbreeding and produce fertile offspring.
• fossils may be formed:

  • from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent
  • when parts of the organism are replaced by minerals as they decay
  • as preserved traces of organisms, such as footprints, burrows and rootlet traces
• • many early forms of life were soft-bodied, which means that they have left few traces behind. what traces there were have mainly been destroyed by geological activity. this is why scientists cannot be certain about how life developed on earth
  • we can learn from fossils how much or how little different organisms have changed as life developed on earth
• extinction

  • permanent loss of all members of a species from an area of the world
• factors affecting extinction

  • new predators
  • new pathogens
  • better competitors
• speciation

  • isolation - two populations of a species become separated
  • genetic variation - each population has a wide range of alleles that control their characteristics
  • natural selection - in each population, the alleles that control the characteristics which help the organism to survive are selected
  • speciation - the populations become so different that successful interbreeding is no longer possible
• resistant bacteria

  • bacteria can evolve rapidly because they reproduce at a fast rate
  • mutations of bacterial pathogens produce new strains. some strains might be resistant to antibiotics so are not killed. they survive and reproduce, so the population of the resistant strain rises. the resistant strain will then spread because people are not immune to it and there is no effective treatment
• to reduce the rate of Development of antibiotic resistant strains:

  • doctors should not prescribe antibiotics innapropriately, such as treating non-serious or viral infections.
  • patients should complete their complete of antibiotics so all bacteria are killed and none survive to mutate and form resistant strains
  • the agricultural use of antibiotics should be restricted
  • the development of new antibiotics is costly and slow. its s unlikely to keep up with the emergence of new resistant strains