DNA differences between same species can be exploited

• Describe gene therapy

  • When a healthy allele is delivered into cells to replace a defective allele
  • The gene can be delivered in 2 different vectors
  • in a plasmid wrapped in a liposome
  • in a virus
• Describe gel electrophoresis

  1. DNA fragments are placed into one side of a gel
  2. A DNA ladder is added - a set of DNA fragments of known length
  3. There is a negative electrode (cathode) next to the DNA fragments and a positive electrode (anode) on the other side
  4. A buffer solution of ions is added to cover the gel
  5. An electrical current is produced which is conducted across the gel by the ions
  6. The DNA fragments move to the anode as they have negatively charged phosphate groups
  7. The smallest DNA fragments move the furthest as they have less resistance in the gel
• What is the separation of DNA fragments based on?

  • The charge
  • The size
• Describe DNA probes

  • Single stranded sections of DNA that are complementary to specific base sequences
  • They are labelled so their complementary base sequences can be detected
• Describe labelling a DNA probe

  1. The probe could be labelled with a fluorescent tag. An optical microscope and UV light is then used to visualise the probe
  2. Or the probe could be labelled with a radioactive isotope of phosphorous. Autoradiography is used to visualise the probe
• Describe locating a specific base sequence using a DNA probe

  1. DNA is amplified using PCR and cut using restriction endonucleases
  2. The DNA fragments are separated using gel electrophoresis
  3. The DNA fragments are absorbed onto a nylon membrane and heated to make the DNA single stranded
  4. A radioactive or fluorescent DNA probe is added which is complementary to the DNA base sequence so it hybridises
  5. The nylon membrane is washed to remove unbound DNA probe
  6. Autoradiography or a UV optical microscope is used to detect it