3/25/2015
How is DNA used to solve crimes?
Review Instructions:
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Get out a separate sheet of notebook paper
Put your name on it
Write your partner’s name under yours
Title the paper- DNA Lecture Review
Both people must record each answer, but I
will only collect one paper to grade, at
random.
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1. What is DNA?
DNA stands for deoxyribonucleic acid and contains genetic
information. It is found on chromosomes located in the nucleus of
our cells.
2. What makes up DNA?
• The sides or backbone of the DNA
molecule are made up of sugar
(deoxyribose) and phosphate
Double Helix
molecules.
• The rungs that form the middle of the
molecule are made up of pairs of
nucleotides or nitrogen bases.
Adenine (A) pairs with thymine (T),
while guanine (G) always pairs with
cytosine (C).
• The order of the bases determines the
DNA Image: http://science.howstuffworks.com/genetic-science/dna-evidence.htm
genetic code.
What is DNA?
http://learn.geneti
cs.utah.edu/conte
nt/molecules/dna/
http://learn.ge
netics.utah.edu
/content/molec
ules/builddna/
Source: Genetics Home Reference
http://ghr.nlm.nih.gov/handbook/basics/dna
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Label the parts of the DNA on your
note-taker
Review:
1. Where are the "instructions" needed for a
living organism to live and grow reside in a
cell?
2. What is the molecule that holds these
"instructions"?
3. How do the nitrogen bases pair as the rungs
on the ladder of DNA?
4. What are the "sentences" found in DNA
called?
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Where is DNA?
DNA is found in the cells in our body.
Nucleus
(Brain of the cell)
Label the parts
of the cell with
DNA on your
note-taker
Mitochondria
(more later)
Where is DNA?
DNA in the nucleus is packaged into Chromosomes
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Where is DNA?
Chromosomes
come in pairs
(one from Mother)
(one from Father)
There are 46
chromosomes in
each somatic
(non sex) cell.
(23 pairs)
Where is DNA?
All types of cells in our body contain a copy of
the same DNA.
Some cells important to forensic science are:
White Blood Cell
Sperm Cell
Buccal (Cheek) Cell
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Review:
5. Where are 2 locations in our cells that
contain DNA?
6. How many pairs of chromosomes do humans
have?
7. What are 2 of the 3 cells that are important
sources of DNA to forensic scientists?
Closing Question:
7. Where may these cells be found at a crime
scene? List at least 3 places.
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4. What are sources of DNA at a Crime Scene?
DNA can be recovered from any substance
that contains cells.
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Blood
Semen
Saliva
Tissue
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Bone
Teeth
Hair
Maggot Crops
5. How is DNA used as evidence?
• Each person’s DNA is different from other people (except
identical twins).
• DNA collected from a crime scene can either link a suspect to the
evidence or eliminate a suspect, similar to the use of fingerprints.
• DNA can identify a victim through DNA from relatives, even
when no body can be found.
• DNA can link crime scenes together by linking the same
perpetrator to different scenes locally, statewide, and across the
nation.
• DNA can place an individual at a crime
scene, in a home, or in a room where the suspect
claimed not to have been.
• DNA can refute a claim of self-defense and put
a weapon in the suspect's hand.
• It can change a story from an alibi to one of
consent.
DNA Strand Image & information : http://www.dna.gov/audiences/investigators/know/
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Review:
9. Write an example scenario of how DNA could
refute a claim of self-defense.
6. What factors affect DNA evidence?
Several factors can affect the DNA left at a crime scene, such as
environmental factors (e.g., heat, sunlight, moisture, bacteria, and
mold). Therefore, not all DNA evidence will result in a usable DNA
profile. Further, DNA testing cannot identify when the suspect was at the
crime scene or for how long.
7. What is CODIS?
CODIS stands for COmbined DNA Index System, which is an
electronic database of DNA profiles that can identify suspects. DNA
profiles from individuals convicted of certain crimes, such as rape,
murder, and child abuse, are entered into CODIS and help officers
identify possible suspects when no prior suspect existed.
Did you know?
Each human cell contains three billion DNA
base pairs. Our unique DNA amounts to 0.1%
or 3 million base pairs.
DNA information : http://www.dna.gov/audiences/investigators/know/
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Review:
10.Write a set of instructions to help prevent
environmental contamination of DNA for
crime scene investigators.
8. True or False?
Circle the true statements
Which three statements below are true?
1. The DNA in a man's blood is the same as the DNA in his skin cells and saliva.
2. Each person's DNA is different from every other individual's.
3. DNA can be found in all the cells in our bodies except the blood cells.
4. DNA can have forensic value even if it is decades old.
5. DNA evidence was first used to get a conviction in a trial in 1987.
Star the true statements (if you got any incorrect)
Watch the video segment from NOVA: "The Killer's Trail"
and be ready to answer the questions on the next slide.
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9. Video Questions:
Watch for the answers to these questions as you watch the video clip.
1. How was DNA evidence used to prove that Dr. Sam
Sheppard did not murder his wife?
2. Why wasn't this evidence used when the case first went to
court?
3. Why do you think the DQA1 test was chosen for DNA
analysis in this case, instead of another, more powerful
genetic test?
4. If the blood trail left at the murder scene wasn't Marilyn's
or Sam's, whose blood might it have been?
5. If you were a juror on this trial, would you be convinced by
the DNA evidence? Why?
Closing Question
• What are the 4 nitrogen bases that
make up the “rungs” on the DNA
ladder?
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