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CHAPTER 13
DNA: The Indispensable
Forensic Science Tool
Cameron Waldron
Forensics
What is DNA
DNA=
The
Deoxyribonucleic acid
molecules carry the body’s genetic
information
Parts
of DNA
 Chromosomes- strands of genetic material
Genes- arranged along the chromosomes like
beads on a thread
DNA at Work
Traits
controlled by DNA come from
proteins.
A protein comes from a link of amino
acids (the building blocks of proteins)
There are 23 pairs of chromosomes
Replication of DNA
It
begins with the unwinding of the
strands in the double helix
PCR (polymerase chain reaction)
Pieces of DNA can be copied with the
aid of a DNA polymerase
Recombinant DNA:
Cutting and Splicing DNA
Genetic
code- the relationship between
the base letters on a DNA strand and the
type of protein specified for manufacture
by the sequence of these letters
Restriction enzymes- chemicals that act as
scissors to cut DNA molecules at specific
locations
DNA Typing
Restriction Fragment Length
Tandem Repeatsregion of a
Polymorphisms
chromosome that contains multiple
copies of a core DNA sequence that
are arranged in a repeating fashion
Restriction Fragment Length
Polymorphisms (RFLPs)- repeat
segments cut out of the DNA double
helix by a restriction enzyme
DNA RFLP process
1.
2.
3.
4.
5.
6.
7.
DNA is cut into fragments
Fragments are separated into bands by
electrophoresis
DNA band pattern is transferred to a
nylon membrane
Membrane with DNA fragments
positioned exactly
Radioactive DNA probe is added
X-ray film placed next to the membrane
to detect the pattern
Developed X-ray film showing DNA
fragment that combined with radioactive
probe
Polymerase Chain Reaction


Primer- short strand of DNA used to
target a region of DNA for replication by
PCR
Steps of the PCR process
1.
2.
3.
Heat the DNA strands to about 94 degrees
Add the primers to the separated strands
Add the DNA polymerase and a mixture of
free nucleotides to the separated strands
Short Tandem Repeats
The
latest method of DNA typing is STR
STRs are locations on the chromosome
that contain short sequence elements that
repeat themselves within the DNA
molecule
Multiplexing- simultaneously detects more
than one DNA marker in a single analysis
Mitochondrial DNA
Mitochondria
are cell structures
found in all of our cells
Sequencing is a procedure used to
determine the order of the base
pairs that comprise DNA
Combined DNA Index System
(CODIS)
CODIS
is a computer software
program developed by the FBI
It lets crime labs to compare DNA
profiles electronically
Collection and Preservation
of
Biological Evidence for
DNA Analysis
Picogram-
one trillionth of a gram
Low Copy Number- fewer than 36
DNA bearing cells
Epithelial Cells- The outer layer of
skin cells
Substrate Control- An unstained
object adjacent to an area upon which
biological material has been deposited