DNA Fingerprinting
DNA - The Molecule
  Three billion bases in
human DNA
  99% of DNA is
identical among
individuals
  1% contains
significant variation
  Each person’s DNA
Profile is unique
  Except Identical Twins
DNA Fingerprints
DNA Fingerprinting can be used to:
1.  Trace the inheritance of genetic
disorders
2.  Identify the origin of a blood, semen, or
saliva sample in a criminal investigation
3.  Establish paternity or maternity
First DNA fingerprint preformed in
1987 in England
Was first used in a case in the US IN
1988
99.9% accurate
Polymerase Chain Reaction
Amplify the amount of
DNA by PCR:
1.  Separate strands
of DNA - Heat
2.  Add primers to the
single strands
3.  Add polymerase and
free nucleotides
4.  Two new DNA
molecules are
formed
Polymorphisms
  A polymorphism is a
variation
  Every 1,000 bases
inherited there is
one variation
  variations allow the
DNA to be cut into
different sized
fragments
  RFLP- Restriction
Fragment Length
Polymorphism’s
RFLP
Steps of making an RFLP:
1.  Add a restriction enzyme to cut the
DNA into fragments - Exact number and
size of fragments produced varies
from person to person
2.  Fragments are separated by
electrophoresis
3.  The smaller fragments travel further
than the large fragments
4.  This creates a DNA Fingerprint
Variable Numbers of
Tandem Repeats (VNTR)
  Most of the DNA in a chromosome
does not code for a gene
  These regions contain sequences
that repeat from 20-100 times (exGTCAGTCAGTCAGTCA)
  There are several known variations
of the Short Tandem Repeats (STR) in
humans
  Ex.- HUMTH01 (repeating AATG) has
seven different variations
Example of STR
VNTR
  Scientists can
look at 4-6
different STR’s in
the same person
  The more STR’s
identified the
higher the
probability of a
match
  VNTR is more
commonly used
than RFLP
Advantages of VNTR
1.  Less complex patterns
in gel
2.  STR’s are less likely to
degrade


Less than 400 base pairs
In the middle of the
chromosome
3.  Can be used on stains
that old or have been
exposed to
decomposition
Mitochondrial DNA
  DNA in the mitochondria
  Inherited maternally
  Forensic Casework
  Analyze sample materials that are not suitable for
nuclear DNA
  Test hair strands without the root
  Test highly degraded tissue
  Test skeletal remains
Problems with mtDNA
  Used for determining maternal
relationships only
  Results take up to two months to
complete
  The specific tested alleles cannot
be compared against standard
tested alleles
  Exclusions are 100%, Inclusions are
95%.
Combined DNA Index
System (CODIS)
  The FBI’s DNA database
  Built from the databases of states that
collect DNA samples from convicted
offenders
1991 - Minnesota was the first state to
match a DNA sample from the scene of a
crime with a sample on file in a database.
MD collects samples from all convicted
felons and some misdemeanor crimes
All states require DNA from sexual
offenders