DNA Profiling
(DNA fingerprinting)
A technique used by scientists to
distinguish between individuals of the
same species using only samples of
their DNA
Who Invented it?
Alec Jeffreys at the University of
Leicester in 1985.
He was knighted in 1994.
Where do you get the DNA?
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All cells in our body
have DNA, but the
riches sources of DNA
that are best for
evidence are found in
…..
Blood
Hair
Saliva
Semen or vaginal fluid
Body tissue cells
DNA in the Cell
chromosome
cell nucleus
Double stranded
DNA molecule
Target Region for PCR
Individual
nucleotides
Stages of DNA Profiling
• Stage 1:
Cells have to be broken down
to release DNA
If only a small amount of DNA is
available it can be amplified using
the polymerase chain
reaction (PCR)
Add chemicals so the DNA is forced
to precipitate out of solution….
• It is white and
gooey and can be
pulled out by
twisting a rod
around it
• 4 base pairs attract
each other to zip up the
double helix.
• Everyones genes have
different combos of
these 4 pairs
Stages of DNA Profiling
• Step 2: add more chemicals
The DNA is cut into fragments using restriction enzymes.
Each restriction enzyme cuts DNA at a specific base
sequence.
This means everyone’s unique DNA is cut into different
size peices.
Stages of DNA Profiling
• The sections of DNA that are cut out are
called restriction fragments.
• This yields thousands of restriction
fragments of all different sizes because
the base sequences being cut may be far
apart (long fragment) or close together
(short fragment).
Stages of DNA Profiling
Stage 3:
• Fragments are
separated on the
basis of size using a
process called gel
electrophoresis.
• DNA fragments are
injected into wells and
an electric current is
applied along the gel.
Stages of DNA Profiling
DNA is negatively
charged so it is
attracted to the
positive end of the
gel.
The shorter DNA
fragments move
faster than the longer
fragments.
DNA is separated on
basis of size.
Stages of DNA Profiling
• A radioactive material
is added which
combines with the
DNA fragments to
produce a fluorescent
image.
• A photographic copy
of the DNA bands is
obtained.
Load gels with crime scene DNA
samples alongside 2 suspects to see
whose DNA fragments match
6
5
4
3
2
1
Suspect 2 DNA 1
Suspect 1 DNA 2
Compare to other students results.
Are they all consistent?
Gel Electrophoresis of DNA
Use these photos in your lab report
6
5
4
3
2
1
Load gels with crime scene DNA
samples alongside 2 suspects to see
whose DNA fragments match
Suspect 2 DNA 1
Suspect 1 DNA 2
Load gels with crime scene DNA
samples alongside 2 suspects to see
whose DNA fragments maych