Genetic screening and counselling

• DNA probes- Short single stranded sequences of DNA:

  • Radioactively or fluorescently labelled
• DNA probes are labelled so that they can be used as markers to locate specific alleles of genes.
• DNA probes are used to locate alleles so that it can highlight disease risks (heritable) or health risks in patients.
• How to add DNA probes via (DNA Hybridization) :

  1. Add DNA probes to solution of alleles of desired genes from patient.
  2. these become mixed as they complement each other.
• To get single stranded from strand:

  1. Using annealing + denaturation
  2. heating breaks the hydrogen bonds (94-96)
• Gel electrophoresis separates DNA fragments by their size.
• Gel electrophoresis:

  1. Add DNA to agar
  2. supply voltage
  3. DNA is negative due phosphate group thus repels from voltage and moves to anode.
  4. this leads to the fragments being separated by size as shorter lengths move quicker to anode.
• Restriction endonucleases (restriction enzymes ) are used to separate DNA into fragments.
• Gel electrophoresis key points:

  • DNA moves toward anode
  • smaller pieces move faster
• Base pairs are suitable to measure length as each base pair occupies the same space and the entirety of DNA is comprised of base pairs.
• Uses of DNA probes:

  • to locate specific alleles
  • to see if a patient carries a mutated allele that causes a genetic disorder
  • Help to determine how patients will respond to drugs
  • identify health risks
• Method to locate genes:

  1. DNA sample is digested into fragments using restriction enzymes and separated using gel electrophoresis.
  2. separated DNA fragments transferred to nylon membrane and incubated with the DNA probe. The probes will only bind to complimentary sequence.
  3. The membrane is exposed to uv light and if gene is present it will fluoresce.
• A micro-ray can be used to screen a sample with multiple DNA probes all at once:

  1. The sample fluorescent DNA is washed over the array which has DNA probes fixed to it
  2. DNA sequences that match the probe stick to the array
  3. The array is washed away to remove fluorescence not attached to probe.
• Genetic counselling is the process of using genetic screening to advise coarse of action on a patients condition.
• Personalized medicine can be used to target different dosages or compounds as medicine depending on the genetic make-up of the person.