DNA Fingerprinting What is DNA Fingerprinting DNA Fingerprinting

DNA Fingerprinting

What is DNA Fingerprinting? • DNA Fingerprinting is a method of developing a person’s DNA “profile”… similar to a fingerprint • This technology was pioneered in England during the mid 1980’s by law enforcement forensic use • DNA evidence exonerated one man, and convicted another (The Blooding by Joseph Wambaugh)

How Does it Work? • Approximately 99. 9% of your DNA is the same as everyone else • The 0. 1% that differs is a combination of: • Gene differences (differences in the genes themselves) • Differences in the regions between genes in the DNA (called polymorphic regions)

How Does it Work? • Certain points between the genes on the DNA have repeating base sequences • For example: ATTACGCGCGCGCTAG C • These are called short tandem repeats (STRs for short)

How Does it Work? • Everyone has STRs at the same place in the DNA but they are different lengths for different people For example: • Person 1: ATTACGCGCGCGTAGC (7 repeats) • Person 2: ATTACGCGCGTAGC (5 repeats) •

How Are They Made? • First, restriction enzymes are used to chop the DNA up into millions of fragments at various lengths • Some of the fragments contain STRs, some do not • The ones that do are different lengths for different people

How Are They Made? • Polymorphisms are slight differences in DNA sequences as seen in individuals of the same species • When using restriction enzymes, we call these polymorphisms: Restriction Fragments Length Polymorphisms (RFLPs)

How Are They Made? • Next, gel electrophoresis is used to sort the DNA fragments by size • Gel Electrophoresis is a method for sorting proteins or nucleic acids based on the electric charge and size

How Are They Made? • Electrical current carries negatively-charged DNA through gel towards positive electrode • The agarose gel filters DNA fragments according to size • Small fragments move farther than large fragments

How Are They Made? • Since STRs are different lengths in different people, this creates a DNA fingerprint

Uses for DNA Fingerprints • FORENSICS • DNA taken from crime scenes (blood, semen, hair, saliva, etc. ) can be compared to the DNA of suspects

• A blood stain was found at the murder scene. The blood belongs to which of the seven possible suspects? Suspect 3

Uses for DNA Fingerprints • PATERNITY TESTS • Since all of our DNA markers came from our parents, DNA fingerprints can be used to determine whether a child and alleged father are related