GENETIC FINGERPRINTING

• WHAT DOES GENETIC FINGERPRINTING RELY ON?

  fact that the genome of most eukaryotic organisms contain repetitive, non-coding bases of DNA
• WHAT ARE VARIABLE NUMBER TANDEM REPEATS?

  non-coding parts of DNA where a short DNA sequence is repeated a variable number of times without spaces, at a single location

  • different in all individuals
  • same in identical twins
  • more similar, the more closely related
• GEL ELECTROPHORESIS?

  • separates DNA fragments by size
  • DNA fragments placed on agar gel
  • voltage applied across it
  • resistance of gel means larger fragments move slower and less distance
  • labelled with radioactive probes
  • detected using X-ray film
  • must use restriction endonucleases on genes if over 500 bases
• MAKING A GENETIC FINGERPRINT?

  STAGE 1 - EXTRACTION

  • extract DNA by separating from rest of cell
  • quantity increased using PCR

  STAGE 2 - DIGESTION

  • cut into fragments using same restriction endonucleases

  STAGE 3 - SEPARATION

  • separated by size
  • gel electrophoresis under electrical voltage
  • immersed in alkali to separate double strands into single strands

  STAGE 4 - HYBRIDISATION

  • radioactive/ fluorescent probes bind with VNTRs
  • complementary base sequence
  • bind under specific temperature/ pH conditions

  STAGE 5 - DEVELOPMENT

  • X-ray film over nylon membrane
  • or located visually
• USES OF GENETIC FINGERPRINTING?

  1. Genetic relationships and variability (paternity/ genetic diversity)
  2. Forensic science
  3. Medical diagnosis (Huntington's disease, over 38 more likely)
  4. Plant and animal breeding (prevent inbreeding, test paternity)
• WHAT IS GENE THERAPY?

  • curing a genetic disease by inserting functional copy of an allele into DNA
  • e.g. cc (cystic fibrosis) to ccC
  • silences faulty or mutated allele so it is not expressed
  • germ line or somatic
  • GERM LINE: sperm/ egg/ zygote/ embryo, permanent but illegal in humans
  • SOMATIC: body cells, legal but temporary
• WHY DO DIFFERENT FRAGMENTS OF DNA MOVE ALONG AGAR PLATE IN GEL ELECTROPHORESIS?

  • different size, therefore different resistances and travel different distances
  • negative charge of DNA is attracted to positively charged anode