DNA Profiling

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•  DNA profiling involves comparison of DNA

DNA profiling is a technique by which individuals can be identified and compared via their respective DNA profiles

  • Within the non-coding regions of an individual’s genome there exists satellite DNA – long stretches of DNA made up of repeating elements called short tandem repeats (STRs) 
  • As individuals will likely have different numbers of repeats at a given satellite DNA locus, they will generate unique DNA profiles 

Comparative STR Lengths at Two Specific Loci


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•  Use of DNA profiling in paternity and forensic investigations

DNA profiling is commonly used in criminal investigations (forensics) and to settle paternity disputes

The procedure involved is common for both:

  • A DNA sample is collected (e.g. from blood, semen, saliva, etc.) and then amplified using PCR
  • Satellite DNA (with STR sequences) are cut with specific restriction enzymes to generate fragments
  • Fragment length will differ between individuals due to the variable length of their short tandem repeats
  • The fragments are separated using gel electrophoresis and the resulting profiles are compared

Forensic Investigations:

Suspects should be a complete match with the DNA sample taken from the crime scene if a conviction is to occur

The number of loci used to generate a unique profile depends on the size of the population being compared

  • E.g. America (population: ~ 320 million) uses 13 loci for comparison; Australia (population: ~ 25 million) uses only 9 loci

Paternity Testing:

Children inherit half their chromosomes from each parent and thus should possess a combination of parental fragments

  • In other words, all fragments produced in the child should also be produced by either the mother or father

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•  Analysis of examples of DNA profiles

Example 1:  Forensic Investigation

  • Compare the DNA collected from the crime scene to determine which of the three suspects was present (click picture to solve)


Example 2:  Paternal Testing

  • Compare the profiles of three men with that of a mother and child to determine the biological father (click picture to solve)

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