DNA and Inheritance

• DNA


  The molecule that contains the genetic code and controls the characteristics of an organism
• Structure of DNA


  • Double helix shape
  • Alternating sugar and phosphate molecules forming the backbone
  • Pairs of complementary bases (A-T, C-G) connecting the backbones
• The order of the bases in DNA determines the order of amino acids in a protein
• DNA profiling/genetic fingerprinting


  The use of unique DNA sequences to identify individuals, used in forensics and classification
• DNA profiling process


  1. Extract DNA from sample

  2. Cut DNA into fragments

  3. Separate fragments by gel electrophoresis

  4. Compare banding pattern to suspect
• Genotype


  The genetic makeup of an organism, the alleles it possesses
• Phenotype


  The physical expression of an organism's characteristics
• Dominant and recessive alleles

  Dominant alleles are always expressed in the phenotype, recessive alleles are only expressed when two copies are present
• Gregor Mendel's work on inheritance laid the foundations of genetics, even though its importance was not recognised until later
• Most phenotypic features are the result of multiple genes, not single gene inheritance
• Sex chromosomes


  The chromosomes that determine biological sex, XX in females, XY in males
• Genetic disorders


  Disorders caused by mutations in genes, e.g. cystic fibrosis
• Family trees can be used to track the inheritance of genetic disorders
• Gene therapy


  The introduction of a correct gene into an organism to treat a genetic disorder
• Arguments for genetic engineering

  • Improved shelf life
  • Resistance to pests and herbicides
  • Resistance to drought and wind
  • Higher yield
  • Improved nutritional value
  • Quicker process than breeding programmes
• Arguments against genetic engineering

  • Cost
  • Public concerns
  • Changing ecosystems
  • Super weeds
  • Need for large trials