DNA profiling
Aka DNA finger printing
We’re all (nearly) unique
Most DNA is highly conservative from one
person to the next
 A few small domains (0.1%) are very
variable
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© 2010 Paul Billiet ODWS
Applications
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Crime scene investigations
Paternity suites and family relationships
Archaeology
Human/family ancestry
Exonerate persons wrongly accused of crimes
Identify catastrophe victims
Identify endangered and protected species as an aid to
wildlife officials (could be used for prosecuting poachers)
Detect bacteria and other organisms that may pollute air,
water, soil, and food
Match organ donors with recipients in transplant programs
Determine pedigree for seed or livestock breeds
Authenticate consumables such as caviar and wine
© 2010 Paul Billiet ODWS
Procedure
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Sample of tissue or cell
DNA extracted
DNA amplified by PCR
DNA fragmented using
restriction enzymes
Gene probes added to identify
fragments
Patterns of fragments of DNA
of known origin & unknown
compared
Control fragments of DNA and
ladders used
© 2010 Paul Billiet ODWS
Image Credit: How Stuff Works
Who is the
father?
Image Credit: How Stuff Works
Restriction Fragment Length
Polymorphism (RFPL)
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Restriction enzymes cut the DNA at particular
base sequences
The presence or absence of these sequences in
the genome will give different lengths of DNA
fragments when they are cut using a particular
restriction enzyme
The DNA fragments are separated by
electrophoresis
DNA probes identify the sequences
Patterns of DNA fragments on the gel can by
used to compare DNA from different samples
Southern Blotting
© 2010 Paul Billiet ODWS
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Short Tandem Repeats (STRs)
Within the human genome there are regions
where a short base sequence is repeated many
times
The number of repeats is very variable
Identified repeats are cut out using a restriction
enzyme
The DNA fragments separated by electrophoresis
The different repeats are identified by DNA
probes with radioactive or fluorescent markers
Samples with the same STRs will show the same
pattern in on the electrophoresis gel
© 2010 Paul Billiet ODWS
Mitochondrial DNA Analysis
Mitochondrial DNA (mtDNA)
 Useful for analysing older tissue samples
 Useful for analysing hair, bones or teeth
 Inherited down the maternal line
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© 2010 Paul Billiet ODWS
Y-chromosome Analysis
Inherited down the paternal line
 Complements mtDNA analysis
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© 2010 Paul Billiet ODWS
Problems
Cost
 Today limited to matches with 4 to 6
probes
 Few probes = greater chance of miss
match
 Contamination of samples
 Degradation of DNA with time
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© 2010 Paul Billiet ODWS