Variation and Evolution

• examples of continuous variation include height and weight
• examples of discontinuous variation include blood groups and eye colour
• when viewed on a graph, continuous variation is presented as a bell shaped curve
• when viewed on a graph, discontinuous variation is presented as a bar chart
• sexual reproduction

  produces a single cell with a new set of pairs of chromosomes
• asexual reproduction 


  produces a number of genetically identical offspring
• new genes can arise as a result of changes (called mutations)
• what can mutation rates be increased by?

  ionising radiation
• natural selection


  a mechanism proposed by Charles Darwin and Alfred Wallace for evolution
• natural selection describes how phenotypes in a population can be maintained or changed to be optimal in the environment
• individuals with characteristics best adapted to their environment are more likely to survive and breed

  successfully
• genes which have enabled better adapted individuals to survive are then passed on to the next generation
• • bacteria naturally include some strains that are resistant to some antibiotics
  • the bacteria are exposed to multiple doses of antibiotic over a period of time
  • the non-resistant bacteria are killed by the antibiotic
  • the resistant strain reproduces and becomes much more common
• gene therapy


  a technique which involves inserting the normal gene into affected lung tissue using an inhaler
• cystic fibrosis


  an inherited disease that causes the production of thick mucus that blocks bronchioles
• cystic fibrosis can be inherited as a recessive allele
• the chance that the child will get cystic fibrosis is 25%

  
• genome


  total genetic information in an organism
• Human Genome Project


  international research project that worked out the sequence of chemical base pairs in human DNA