Forensic Analysis

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Forensic Analysis

• Who did it?

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Sampling

• Gather samples from crime scene
• Blood
• Semen
• Hair
• Skin cells
• Collect samples from suspects

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Types of Data Analysis

• Blood typing/Tissue typing
• Large amounts of blood or semen
• Minimal amount of info
• Can prove innocence, but not guilt
• RFLP or DNA fingerprint
• Small amounts of sample
• Only 1,000 cells
• Must PCR amplify the DNA to make many copies of
  the gene of interest
• Analyze chromosomal DNA
• Unique to individuals
• Can prove guilt

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How does PCR work?

• Multiple replication events in a tube
• DNA polymerase (called Taq polymerase)
• Nucleotide monomers (A,T,G,C)
• Template DNA that contains gene of choice
• Primers

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How do restriction enzymes work?

• Restriction enzymes cut DNA at very specific
  sequences
• EX)Enzyme x cuts every sequence that looks like
  this CCGG or GGCC and it cuts between the Cs
• The DNA fragments that result are called
  restriction fragments
• The number of restriction fragments and their
  sizes reflect the specific sequence of
  nucleotides in DNA

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Restriction Fragments
Person 1 3 fragments W (medium), X (large), Y
(small)
Person 1
Person 2 2 fragments Z (large), Y (small)
Person 2
DNA from Two Different people
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How does gel electrophoresis work?

• Gel is made of agarose (like gelatin)
• Put DNA fragment mixtures into gelatin
• DNA has negative charge
• Negative charge is attracted to positive charge
• Apply a positive charge to one side of gel and
  negative to other?DNA moves toward positive
• Larger DNA moves slower than smaller DNA
• Larger DNA heavier and more difficult to move

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Agarose Gel
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Fingerprint Patterns
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Analysis
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Bonus questions

• Why does DNA move on a gel during electrophoresis
• A. Because DNA has a negative charge
• B. Because it is cut with restriction enzymes
• C. Because DNA has a positive charge
• D. Because DNA codes for enzymes
• What do restriction enzymes do?
• A. They cut DNA into codons
• B. They only cut guilty peoples DNA
• C. They cut DNA at very specific areas
• D. They cut proteins into small pieces

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• Using a DNA fingerprint analysis to prove a
  persons guilt in a crime involves which of the
  following?
• A. PCR of DNA from victim sample and suspect
  sample
• B. Cutting DNA with restriction enzymes
• C. Gel electrophoresis
• D. DNA extraction
• E. All of the above
• PCR is most similar to which biological event?
• A. Translation
• B. Transcription
• C. Replication
• D. Mutation

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• Which of the following is true?
• DNA can be copied outside of a cell
• DNA can be separated according to size using gel
  electrophoresis
• 2 DNA strands that are exactly alike will be cut
  in the same places by the same restriction
  enzymes
• All of the above
• None of the above