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Dna Technology


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  • 1. DNA TECHNOLOGY DNA Profiling & Identification
  • 2. Use of DNA
    • since 1987, DNA analysis has made appearances in US courtrooms
    • originally known as “DNA fingerprinting” it is now called DNA profiling or typing
    • used in less than one percent of all criminal cases
  • 3. Use of DNA
    • can quickly eliminate a suspect, saving time in searches for perpetrators
    • provides compelling evidence to support a conviction
    • reduces the chance of a wrongful conviction
  • 4. Success of DNA in Courtroom
    • depends on
      • proper handling of evidence
      • careful unbiased analysis
      • fair & appropriate interpretation of results
      • accurate & effective reporting of results to judges and jurors
  • 5. Methods of DNA Analysis
    • Restriction Fragment Length Polymorphism (RFLP)
    • Polymerase Chain Reaction (PCR)
    • Short Tandem Repeat (STR)
    • Mitochondrial DNA (mtDNA)
    • Y-Chromosome Analysis
  • 6. RFLP - restriction
    • analyzes the variable lengths of DNA fragments resulting from being cut with a restriction enzyme
    • enzyme cuts DNA at a specific sequence pattern known as a recognition site
    • presence or absence of recognition sites in a DNA sample generates DNA fragments of variable lengths
  • 7. RFLP – gel electrophoresis
    • restricted DNA placed in well of gel in an electrophoresis tank and current is applied
    • DNA is negatively charged and will travel to the positive side of the tank
    • large pieces travel slowly, small pieces travel quickly
  • 8. RFLP – hybridization
    • fragments are hybridized – DNA probes bind to complementary DNA sequences in the sample
    • probes are usually radioactive and will expose an x-ray film (autoradiography)
    • increasing # of probes decreases the chance of a coincidental match
  • 9. RFLP - analysis
    • probed fragments exposed on film create a profile that can be compared to known samples
    • any profiles that are being compared must be run on the same gel
  • 10. RFLP – pros/cons
    • 1 st application of DNA analysis to forensics
    • gives a positive match
    • not used widely today due to need for a relatively large amount of DNA
    • samples degraded by the environment do not work well
  • 11. PCR Analysis
    • used to make millions of exact copies of DNA from a sample (amplification)
    • sample can be as small as a few skin cells
    • highly degraded samples can be analyzed
    • prevention of contamination extremely important
  • 12. STR Analysis
    • used to evaluate specific regions (called loci) within DNA
    • variability in short tandem repeat regions can be used to distinguish one DNA profile from another
  • 13. STR Analysis
    • FBI uses a standard set of 13 specific STR regions of CODIS
    • odds of two people having the same 13 loci DNA profile is about 1 in a billion
  • 14. mtDNA Analysis
    • used to examine DNA from samples that cannot be analyzed by RFLP or STR which require nuclear DNA
    • all mothers have the same mtDNA as their daughters b/c mitochondria of each new embryo comes from the mother’s egg cell
  • 15. mtDNA Analysis
    • older samples that lack nucleated cellular material (like bones, teeth, hair) can be analyzed via this method
    • comparing mtDNA profile of unidentified remains with profile of potential maternal relative can be important technique
  • 16. Y-Chromosome Analysis
    • Y chromosome passed directly from father to son
    • analysis of genetic markers on Y chromosome useful for
      • tracing relationships among males
      • analyzing biological evidence involving multiple male contributors