CB4

• Natural selection


  By chance, the variations of some individuals make them better at coping with the change than others, and more likely to survive (also called 'survival of the fittest')
• Inheritance


  The survivors breed and pass on their variations to their offspring. So the next generation contains more individuals with the 'better-adapted variations'
• Evolution


  A gradual change in the characteristics of a species over time
• During the 18th century, people started to accept that organisms slowly evolve into others
• When conditions change


  Some individuals are better adapted to cope than others
• Evolution rarely happens in one neat line - there are usually many branches
• In conditions of medium temperature and ample resources, all the animals in the population could survive and reproduce
• When conditions change, some individuals are better adapted to cope than others
• Darwin's idea


  1. Genetic variation

  2. Environmental change

  3. Natural selection

  4. Inheritance

  5. Evolution
• Evolution


  If the environmental conditions remain changed, natural selection occurs over and over again, and a new species evolves with all the individuals having the 'better-adapted variations'
• In the 1940s and 1950s, a substance called warfarin was used to poison rats. When it was first used, most rats died, but within 10 years most rats were resistant to (not affected by) warfarin
• Due to genetic variation there had always been some rats that were resistant. As the poison killed the non-resistant rats, the only ones left to breed were resistant
• The same thing has happened with bacteria and antibiotics (drugs that kill bacteria). In a population of bacteria, some bacteria are more resistant than others and take longer to be killed
• People who take an antibiotic to treat an infection often stop taking it too early, because they feel better. This leaves resistant bacteria still alive. They reproduce and spread, causing infections that cannot be treated with the antibiotic because all the bacteria are now resistant
• This problem of resistance in bacteria was not present when antibiotics were first used
• Antibiotic resistance in bacteria


  1. Bacteria in a population show variation in the amount of resistance to an antibiotic

  2. With time, the antibiotic kills more and more of the bacteria. The most resistant bacteria take the longest to die

  3. The resistant bacteria survive and reproduce

  4. The new population of bacteria are all now resistant to the antibiotic
• GMO


  Genetically modified organism
• Allele


  Different forms of a gene
• Genes exist in different forms, called alleles, which cause variation in characteristics
• In selective breeding, only certain alleles are selected. Others become rare or disappear
• Farming huge numbers of the same breed or variety is a problem as all the organisms are very similar
• Animal welfare is a concern with selective breeding, e.g. some selectively bred chickens produce so much breast meat they can hardly stand up
• Scientists now save the seeds of thousands of different plant varieties in seed banks
• GM crops


  • They have been produced to be resistant to some insects (so less insecticide is needed)
  • They are resistant to certain herbicides (weed killers) which then kill weeds but not the crop
• The seeds for many GM plants are expensive
• Some people think that GM crops will reproduce with wild plant varieties and pass on their resistance genes, and these genes may also have unknown consequences in wild plants
• Some people think that eating GM organisms may be bad for health (but there is not evidence to support this)
• Recombinant DNA


  DNA combined in a new way
• Genetic engineering of a bacterium


  1. Restriction enzymes cut DNA

  2. Sticky ends are joined using ligase

  3. Plasmids with new genes are inserted into bacteria
• Vector


  Any DNA molecule used to carry new DNA into another cell
• Campaigners often destroy GM crops during trials
• Some people think GM will be bad for them
• What are the steps of natural selection?


  1. There is an overproduction of offspring.
  2. Genetic variation exists within the population as new alleles are formed from mutations.
  3. They compete to survive and to gain resources- this acts as a selection pressure.
  4. Some individuals will be better adapted to the selection pressure in the environment and survive as they have the advantageous alleles. The less adapted will die.
  5. Those that survive will breed and reproduce.
  6. The advantageous alleles will be passed on to their offspring over many generations.
• What is a mutation?


  A random change in the DNA base sequence.
• Recall some features of Ardi (Ardipithecus ramidus)


  Existed 4.4 million years ago.

  Height: 120cm

  Brain size: 350cm3.

  Other details: a tree climber, bipedal (walked upright), had long arms, had long big toes (to the side).
• Recall some features of Lucy (Australopithecus afarensis)


  Existed 3.2 million years ago.

  Height: 107cm

  Brain size: 400cm3

  Other details: bipedal (walked upright), had a face that was ape-like, feet like humans.
• Recall some features of the Turkana Boy (Homo erectus)


  Existed 1.6 million years ago

  Discovered by Leakey

  Height: 179cm

  Brain size: 850cm3 - 1100cm3

  Other details: long distance walker
• How do fossils and stone tools provide evidence for human evolution


  Fossils- the brain size increased (the skull was getting bigger) which indicates they got smarter.

  Stone tools- became more complex and had a greater variety as the species was getting smarter.
• How are stone tools dated


  1. Stratigraphy- using the rock layers the stone tools are found in. The deeper the stone tool, the older and simpler it is.
  2. Carbon dating- rock layers can be used to work out the ages of the stone tools. (done on living organisms in the rock layers).
• What is an adaptation


  A change which allows an organism or species to become better suited to its environment.