2.2 inheritance, variation and evolution

• What is variation?

  Differences in characteristics of individuals
• What are the two causes of variation within a species?

  Genetics and environment
• What is genetic variation?

  Variations in genotypes due to different alleles
• What creates genetic variation in a species?

  Spontaneous mutations and sexual reproduction
• What is a mutation?

  A random change to the DNA base sequence
• What are the three types of gene mutation?

  Insertion, deletion, and substitution
• How may a gene mutation affect an organism’s phenotype?

  It can be neutral, minor, or severe
• What is the consequence of a new phenotype caused by a mutation being suited to an environmental change?

  There will be a rapid change in the species
• What is evolution?

  A gradual change in inherited traits over time
• What is the theory of natural selection?

  All species evolved from simple life forms
• Outline the steps of natural selection.

  1. Genetic variation exists due to mutations.
  2. Selection pressures exist (e.g. competition).
  3. Random mutation gives a selective advantage.
  4. Organism is better adapted and survives.
  5. Organism reproduces, passing on beneficial alleles.
  6. Frequency of advantageous alleles increases.
• How do two populations become different species?

  When their phenotypes prevent interbreeding
• What is selective breeding?

  Humans breed organisms with desirable traits
• Outline the main steps involved in selective breeding.

  1. Identify a desired characteristic.
  2. Select parent organisms with desired traits.
  3. Breed selected offspring with desired traits.
  4. Repeat until all offspring have desired traits.
• What is the main advantage of selective breeding?

  Creates organisms with desirable features
• Where else is selective breeding useful besides agriculture?

  In medical research and sports
• Outline the disadvantages of selective breeding.

  • Reduction in the gene pool
  • Inbreeding results in genetic disorders
  • Development of physical problems
  • Potential to select harmful recessive alleles
• What is genetic engineering?

  Modification of an organism's genome
• What is a use for genetically modified bacteria cells?

  To produce human insulin for diabetes
• Describe the benefits of genetic engineering.

  • Increased crop yields for growing population
  • Useful in medicine (e.g. insulin-producing bacteria)
  • GM crops produce scarce resources (e.g. GM golden rice)
• Describe the risks of genetic engineering.

  • Long-term effects of GM crops unknown
  • Negative environmental impacts
  • Late-onset health problems in GM animals
  • GM seeds are expensive
• What is the name for crops that have had their genes modified?

  Genetically modified (GM) crops
• What is Bacillus thuringiensis (Bt)?

  A bacterium that kills insect larvae
• How is genetic engineering used to protect crops against insects?

  • Isolate the gene for toxin production in Bt.
  • Insert it into the DNA of crops.
  • Bt crops secrete the toxin to kill insect larvae.
• What are the benefits of Bt crops?

  • Increased crop yields
  • Less need for artificial insecticides
  • Toxin is specific to certain insect larvae
• What are the risks of Bt crops?

  • Long-term effects of Bt crops unknown
  • Insect larvae may become resistant
  • Killing insect larvae reduces biodiversity
• Describe the process of genetic engineering.

  1. DNA is cut by restriction enzymes.
  2. Vector DNA is cut to create sticky ends.
  3. Ligase enzymes join DNA and vector DNA.
  4. Recombinant DNA is taken up by target cells.
• What is a vector in genetic engineering?

  A structure that delivers a gene
• How can plants be cloned?

  • Taking plant cuttings
  • Tissue culture
• What is tissue culture?

  Using small groups of cells to grow plants
• Describe how plants are grown using tissue culture.

  1. Select a plant with desired characteristics.
  2. Cut small samples from meristem tissue.
  3. Grow in a petri dish with growth medium.
  4. Transfer to compost for further growth.
• What must be ensured when preparing tissue cultures?

  Ensure aseptic conditions to prevent contamination
• What does the growth medium contain?

  Nutrients and growth hormones
• What are the advantages of growing plants by tissue culture?

  • Fast and simple process
  • Requires little space
  • Grows many clones with desirable traits
  • Useful in preserving endangered species
• What are the disadvantages of growing plants by tissue culture?

  • Reduction in the gene pool
  • Low survival rate of plant clones
  • May increase harmful recessive alleles
• Describe the plant cuttings method of plant cloning.

  • Older but simpler method than tissue culture
  • Produces identical new plants from a parent plant
• Detail the process of the plant cuttings method of plant cloning.

  1. Cut a branch from the parent plant.
  2. Remove lower leaves and plant the stem.
  3. Use plant hormones to encourage root development.
  4. Cover with a plastic bag to keep warm and moist.
  5. New roots and plant form after a few weeks.
• What does embryo transplanting involve?

  • Splitting pre-specialised cells from an embryo
  • Transplanting identical embryos into host mothers
• Describe how adult cell cloning is performed.

  1. Remove nucleus from an unfertilised egg cell.
  2. Insert nucleus from an adult body cell.
  3. Electric shock stimulates division to form an embryo.
  4. Insert embryo into uterus of an adult female.
• What is sexual reproduction?

  Type of reproduction involving gametes.