Brent Cornell

    
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

    
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

    
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)