Crime
Scene
Investigation
Who Ate The Cheese?

Oh no! Someone
ate the Queen’s
prize Limburger
cheese!
 Saliva samples were
taken from the teeth
marks left on the
cheese

How can we
determine who ate
the cheese?
DNA Fingerprinting

A process which uses
fragments of DNA to
identify the unique
genetic makeup of an
individual.
1. PCR
2. Restriction Enzymes
3. Electrophoresis
PCR

Polymerase Chain Reaction
– Replicates DNA sample
– Produces millions of copies in 2 hours
Restriction Enzymes
Molecules that cut DNA segments into
smaller pieces by breaking bonds
 Cuts DNA into fragments of different
lengths

Gel Electrophoresis

GEL ELECTROPHORESIS
– DNA molecules have a negative charge.
– The molecules migrate toward the positive
pole.
– The larger the molecule, the more difficult it
is to make its way through the gel, so the
shorter segments move farther than longer
ones.
DGGE
Denaturing gradient gel electrophoresis
 DNA melts!
 Temperature of melting point
determined by G/C content
 Can separate DNA by melting point =
different genes

Who ate the cheese?

Today you are going to solve a crime
using the techniques you just learned!
Crime Scene Photo