Download DNA - JSH BIOLOGY with Ms. Barbanel

What do these items have to do
with one another?
Deoxyribonucleic Acid (DNA)
Unit 8A
Forensic Science
Unit 8A: DNA – Contents
1. Structure of DNA
2. DNA Typing
3. Collecting and Packaging Biological Evidence
4. Isolating DNA
5. DNA Sequencing: PCR
6. DNA Sequencing: Gel Electrophoresis
7. CODIS
1. Structure of DNA
a. Like fingerprints, DNA is unique to each
individual  individual evidence!
b. DNA can definitively link a suspect to a victim
or crime scene.
c. The primary unit of DNA is called a gene
d. Each gene contains instructions that control our
genetic traits
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1. Structure of DNA
double
helix
e. DNA (deoxyribonucleic acid) is a molecule
comprised of repeating units called nucleotides
– A nucleotide consists of
• Sugar-phosphate backbone
– Deoxyribose sugar
– Phosphate
• Nitrogenous base
– adenine, guanine, cytosine, thymine
f. Adenine bonds only to thymine, and
guanine bonds only to cytosine
g. The order of bases is our genetic code.
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1. Structure of DNA
• Four types of
bases are
associated
with the DNA
structure:
adenine (A),
guanine (G),
cytosine (C),
thymine (T).
1. Structure of DNA
h. The long strands of DNA are coiled upon
themselves into shapes called chromosomes
– When paired, chromosomes resemble the letter X
i. Humans have 22 pairs of autosomal
(standard) chromosomes, and 1 pair of 2 sex
chromosomes
– Females are XX
– Males are XY
Unit 8A: DNA – Contents
1. Structure of DNA
2. DNA Typing
3. Collecting and Packaging Biological Evidence
4. Isolating DNA
5. DNA Sequencing: PCR
6. DNA Sequencing: Gel Electrophoresis
7. CODIS
2. DNA Typing
a. DNA typing (a.k.a. DNA Fingerprinting) was
developed by British geneticist Sir Alec Jeffreys
in 1984.
b. This technique converts DNA into readable
bands on a gel
With these bands, we
can compare suspect
and crime scene DNA,
or child and possible
father, etc.
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2. DNA Typing:
Short Tandem Repeats (STRs)
Short Tandem Repeats (STRs):
a. A common method of DNA typing
b. There are locations (loci) on a chromosome that
contain short segments of 3 – 7 bases that repeat
themselves
c. STR’s are less susceptible to degradation (breaking
down) and can be recovered from bodies or stains
that have been subject to extreme decomposition
d. With the technology of PCR one can extract and
amplify a combination of different STR’s.
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2. DNA Typing:
Short Tandem Repeats (STRs)
Short Tandem Repeats (STRs):
e. Serve as useful markers for identification
because they are found in great abundance
throughout the human genome.
f. What is important to understand is that all
humans have the same type of repeats, but there
is tremendous variation in the number of repeats
each of us have.
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Unit 8A: DNA – Contents
1. Structure of DNA
2. DNA Typing
3. Collecting and Packaging Biological Evidence
4. Isolating DNA
5. DNA Sequencing: PCR
6. DNA Sequencing: Gel Electrophoresis
7. CODIS
3. Collecting and Packaging
Biological Evidence
At the crime scene, the following are to be
collected and sent to the forensic laboratory:
1.
2.
3.
4.
5.
Victim’s clothing
Fingernail scrapings
Head and pubic hairs
Blood
Other sources of DNA
3. Collecting and Packaging
Biological Evidence
Other possible
sources of DNA
•
•
•
•
•
•
Skin
Sweat
Blood
Mucus
Saliva
Tissue
•
•
•
•
•
Semen
Urine
Hair (root)
Ear Wax
Vaginal or rectal
cells
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3. Collecting and Packaging
Biological Evidence
a. Photograph evidence first
b. Wear gloves at all times
c. Package each stained article separately
in paper or a well-ventilated box (to
avoid bacterial or fungal growth)
d. Remove dried blood using a sterile
swab moistened with distilled water
e. Store biological evidence in the
refrigerator or a cool location until it is
delivered to the lab
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Unit 8A: DNA – Contents
1. Structure of DNA
2. DNA Typing
3. Collecting and Packaging Biological Evidence
4. Isolating DNA
5. DNA Sequencing: PCR
6. DNA Sequencing: Gel Electrophoresis
7. CODIS
4. Isolating DNA
Most DNA extraction procedures consist of two
parts:
1. A technique to lyse (cut open) the cells and
expose the DNA
2. An enzyme or chemical wash to remove
contaminates such as: proteins, RNA, or
macromolecules
Unit 8A: DNA – Contents
1. Structure of DNA
2. DNA Typing
3. Collecting and Packaging Biological Evidence
4. Isolating DNA
5. DNA Sequencing: PCR
6. DNA Sequencing: Gel Electrophoresis
7. CODIS
5. DNA Sequencing: PCR
5. DNA Sequencing: Polymerase
Chain Reaction (PCR)
a. A technique for making many copies of a specific
piece of DNA to be analyzed forensically
– Can amplify very minute quantities of DNA millions of
times!
b. This method works by cycling
through different temperatures
for each part of the process
c. A device called a thermocycler controls the
temperatures, allowing for fast and accurate
copying of DNA
5. Polymerase Chain Reaction
(PCR)
d. The steps of PCR
Step 1: Denaturation.
– Extracted and purified DNA is heated to “unzip”
(separate) the double helix
– This is done at high temperature, about 94°C
5. Polymerase Chain Reaction
(PCR)
d. The steps of PCR
Step 2: Annealing.
– Short template pieces called “primers” bind with the
separated strands for new DNA to build upon.
– This occurs at ~65°C
5. Polymerase Chain Reaction
(PCR)
d. The steps of PCR
Step 3: Extension/Elongation.
– Taq Polymerase, a DNA building enzyme, adds free
nucleotides from the surrounding solution onto the
template primers
– In this way, new strands are built out of the original 2
separated stands
– This happens at 72°C
new DNA
strands
5. Polymerase Chain Reaction
(PCR)
e. Each step only requires a few minutes
f. The thermocycler machine cycles through
these temperatures for several hours
g. Each cycle doubles the number of copied
DNA strands
PCR is specific to your
“region of interest.” Different
primers will selectively
amplify different genes
Unit 8A: DNA – Contents
1. Structure of DNA
2. DNA Typing
3. Collecting and Packaging Biological Evidence
4. Isolating DNA
5. DNA Sequencing: PCR
6. DNA Sequencing: Gel Electrophoresis
7. CODIS
6. Gel Electrophoresis
6. Gel Electrophoresis
a. DNA can be visualized through the
process of electrophoresis
b. In the lab, DNA molecules are cut by
restriction enzymes into fragments of
various sizes. Restriction enzymes cut
at specific sequences throughout the
DNA.
c. The resulting fragments are forced to
move along a gel-coated plate under the
influence of an electrical field.
6. Gel Electrophoresis
d. The DNA molecules
have a slight negative
charge, so they are
attracted to the positive
end of an induced
electric field.
e. DNA fragments are
separated by size
– Larger fragments move
more slowly
– Smaller fragments move
farther along the gel
6. Gel Electrophoresis
f. After the fragments have
“migrated” across the gel,
the gel can be stained to
show the “bands” or
fragments easily
g. Then comparisons can be
made
– Example: crime scene sample
to suspect
Unit 8A: DNA – Contents
1. Structure of DNA
2. DNA Typing
3. Collecting and Packaging Biological Evidence
4. Isolating DNA
5. DNA Sequencing: PCR
6. DNA Sequencing: Gel Electrophoresis
7. CODIS
7. Combined DNA Information
System (CODIS)
• CODIS maintains a
database of DNA profiles
from
–convicted offenders
–unsolved crime scene
evidence
–profiles of missing
persons
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Resources
• Saferstein, Richard. Forensic Science: An Introduction. New
Jersey: Pearson Prentice Hall, 2008
• Saferstein, Richard. Forensic Science: An Introduction. 2nd
ed. New Jersey: Pearson Prentice Hall, 2011
• Saferstein, Richard. Criminalistics: An Introduction to
Forensic Science. 8th ed. Upper Saddle River, NJ; Pearson
Prentice Hall, 2004
• http://law2.umkc.edu/faculty/projects/ftrials/clinton/lewinskyd
ress.html
• http://www.trutv.com/library/crime/notorious_murders/famous
/simpson/index_1.html
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