Variation and evolution

• Types of Reproduction


  • Sexual
  • Asexual
• Sexual reproduction


  • 2 Parents
  • Gametes are produced with half of the genetic information of both parents
  • A combination of these gametes at fertilisation produces new offspring
• Asexual reproduction


  • 1 Parent
  • Offspring are produced from 1 parent
  • No energy is wasted on gametes and finding a mate meaning a lot of offspring can be produced quickly
  • Offspring show genetic variation and as a species are more likely to survive sudden environmental change
  • No genetic variation, Offspring are clones of the parent; they are genetically identical
• Causes of variation


  • Genetic factors
  • Environmental factors
• Genetic factors


  Characteristics caused by genes, inherited from parental DNA (e.g. eye colour, blood type, being able to roll tongue, flower colour)
• Environmental factors


  Characteristics that change due to the environment (e.g. language development, tattoos and piercings, competition in plants reducing access to light or water restricting growth)
• Most variation is not caused by just one gene but by groups of genes or a combination of both genetic and environmental factors
• Evolution


  Variations in species that can be inherited (are heritable) are the basis of evolution
• Theory of evolution by natural selection

  1. Mutation

  2. Variation

  3. Competition

  4. Survival of the fittest

  5. Breeding
• If environmental change is too quick for species to adapt by natural selection extinction may occur
• Types of variation


  • Continuous variation
  • Discontinuous variation
• Continuous variation


  Controlled by more than one gene and environmental factors such as height and weight
• Discontinuous variation


  Usually controlled by one gene and so individuals fit clearly into discrete groups such as eye colour, blood type
• Mutation


  A change in a gene, they occur randomly but the rate of mutation can be increased by ionising radiation, some mutations can be inherited and cause disease
• Genetic disease


  • Cystic fibrosis
• Cystic fibrosis


  • Causes thick sticky mucus that block bronchioles in the lungs
  • Gene therapy can be used to treat the disease but is not a cure as the gene is not copied as cells renew
• If both parents carry the recessive Cystic fibrosis gene

  There is a ¼ chance that a child will have the disease
• Modelling natural selection


  1. Arrange small pieces of plain and patterned card on a plain background

  2. Use forceps to model a predator beak/jaw and record how many of each type of card you pick up in 15 seconds

  3. This shows that you are more likely to select prey that is more easily seen (less camouflaged), leaving the camouflaged organisms to breed and pass on their genes
• Limitations of the natural selection model include: the model prey does not move, the model background is flat not textured
• Studying human DNA through the Human Genome Project gives us more information to develop new ways to treat, cure, or even prevent disease