Variation

• Variation

  There are differences in characteristics between members of the same species
• Variation can be

  • Acquired during life of organism (riding a bike)
  • Inherited/genetic: can be passed on to the next generation by sexual reproduction (tongue rolling)
• Sexual reproduction

  Responsible for most of variation that are in offspring
• Variation caused by sexual reproduction reasons

  1. Independent assortment: to the way in which chromosomes enter into gametes at meiosis
  2. Crossing over of chromosomes: this produces a combination of genes from the mother and father
  3. Recombination: at fertilisation each egg and sperm represents a one in eight million combination of chromosomes, which shows that sexual reproduction produces a huge range of genetic variation
• Species

  A group of similar organisms that are capable of interbreeding and producing fertile offspring
• Mutation

  Any sudden change in the amount or structure of DNA
• What can result from an uncontrollable rate of mitosis

  Cancer
• Causes of cancer

  • UV radiation
  • Smoking
• Spontaneous mutations occur naturally when DNA does not produce exact copies of itself
• Mutations are caused by mutagens
• Gene mutation

  Changes in a single base pair within a gene e.g cystic fibrosis / haemophilia
• Chromosome mutation

  Large changes of base pairs in the structure or number of one or more chromosomes eg Downs syndrome caused by extra chromosome (3 at 21st chromosome - Trisomy 21)