CHAPTER 9
DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL
1.
Learn the parts of a nucleotide and know how they are linked together to make
DNA.
2.
Understand how DNA strands coil into a double helix.
3.
Describe the concept of base pairing as it relates to the double helix structure of
DNA.
4.
Explain how the sequence of bases along a DNA strand ultimately determines
the structure of proteins that are synthesized within the body.
5.
Describe how a double-strand DNA replicates itself. What are the implications
of this process for forensic science?
6.
Understand how DNA can be cut and spliced into a foreign DNA strand.
7.
Describe some commercial applications of this recombinant DNA technology.
8.
Explain the difference between DNA strands which code for the production of
proteins and those strands which contain repeating sequences of bases.
9.
Explain what is meant by a restriction fragment length polymorphism (RFLP).
10.
Describe the process of typing DNA by the RFLP technique and explain how
DNA band patterns are interpreted.
11.
Explain the technology of polymerase chain reaction (PCR) and how it is
applied to forensic science.
12.
Explain the latest DNA typing technique, Short Tandem Repeat (STR) analysis.
13.
Explain the difference between a traditional STR analysis and a Y-chromosome
STR determination.
14.
Explain the difference between nuclear DNA and mitochondrial DNA.
15.
Discuss the application of a DNA computerized database to criminal
investigation.
16.
List the necessary procedures to be taken for the proper preservation of
bloodstained evidence for laboratory DNA analysis.
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SUPPLEMENTARY QUESTIONS AND ANSWERS
d
1. Examples of polymers that contain repeating units known as nucleotides are:
a. Hemoglobin
b. Starch
c. Cellulose
d. DNA
e. Paints
b
2. How many different bases are associated with the makeup of DNA?
a. 3
b. 4
c. 5
d. 6
e. None of the above
d 3. Assume that two strands of DNA have been separated and that the base
sequence on one strand is ATGC. State the sequence of bases on the second strand.
a. GCAT
b. ACTC
c. TGGC
d. TACG
e. GACG
b
4. The production of amino acid is coded by a sequence of how many bases on the
DNA molecule?
a. 2
b. 3
c. 4
d. 5
e. 6
c
5. Portions of the DNA molecule useful for DNA typing:
a. Code for the production of proteins
b. Are useful for recombinant DNA
c. Are repeated many times
d. Are useful for the production of insulin
e. Can determine if a person has sickle-cell anemia
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e
6. The following steps comprise the DNA typing process: (l) electrophoresis, (2)
Southern blotting, (3) hybridization with a radioactive probe, (4) digestion with
restriction enzyme, (5) process with X-ray film. List these steps in their proper
sequence.
a. 1,2,3,4,5
b. 2,1,3,4,5
c. 4,5,1,2,3
d. 5,4,3,2,1
e. 4,1,2,3,5
d
7. Which of the following statements is FALSE?
a. RFLP and STR segments are both tandem repeats.
b. RFLP strands are more likely to decompose as compared to STRs.
c. RFLP strands are too long to be amplified by PCR.
d. RFLP DNA strands are much shorter in length than STRs.
e. STRs can be detected at levels that are more than fifty times more sensitive
than RFLPs.
c 8. The concept of simultaneously extracting, amplifying, and detecting a
combination of STRs is known as:
a. PCR
b. THO1
c. Multiplexing
d. Electrophoresis
e. Polymarker
c
9. Which statement is NOT correct for Y-STRs?
a. Female STRs will not yield a Y-STR profile.
b. Y-STRs can be amplified by PCR.
c. Y-STR types are typically shorter in length compared to X-STRs.
d. A typical Y-STR pattern has one band.
e. Y-STRs are less susceptible to degradation compared to RFLPs.
e 10. Which of the following statements about mitochondrial DNA is INCORRECT?
a. Mitochondrial DNA is located outside the cell’s nucleus.
b. Mitochondrial DNA is constructed in a loop configuration.
c. Two regions of mitochondrial DNA have been found to be highly variable
in the human population.
d. Many copies of mitochondrial DNA’s hypervariable regions are made by
PCR.
e. The number of repeat segments found in the hypervariable regions are used
to type mitochondrial DNA.
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b 11. A conventional STR profile emanating from a mixture of DNA from male
donors yields four peaks or bands for each locus present. How many peaks or
bands would you normally expect for each locus if a Y-STR profile is
performed on the same sample?
a. One
b. Two
c. Three
d. Four
e. One to three
12.The victim of a homicide is wrapped in a blood-soaked sheet. Describe the proper
steps to be taken in order to preserve the sheet for laboratory examination. List all
necessary submissions that must be made for a thorough examination of blood evidence.
A proper answer should include the following points:
a. The sheet must be air-dried out of the presence of direct sunlight or heat.
b. The evidence collector must handle the sheet with a minimal amount of
personal contact. All body fluids must be assumed to be infectious; hence,
wearing disposable latex gloves while handling the evidence is required.
Latex gloves will also significantly reduce the possibility that the evidence
collector will contaminate the evidence through perspiration.
c. The sheet is to be wrapped separately from other evidence. A paper bag or
well-ventilated box is recommended. Refrigerate the container or store it in
a cool location out of direct sunlight until delivery to the laboratory.
d. Have a physician or nurse collect a minimum of 7 cc. of blood from the
victim and all suspects in a vacuum tube that doesn’t contain either a
preservative or anticoagulant. Also, collect a minimum of 7 cc. of blood
containing the anticoagulant EDTA. This blood will be used for DNA
testing. Alternatively, a buccal swab can be obtained from each individual.
e. Label all evidence containers. The evidence collector’s name or initials, the
date, and the sampling locations are to be shown. All items collected are to
be described in the evidence collector’s field notes.
Review Questions—9
1.
The fundamental unit of heredity is the ___________.
2.
Each gene is actually composed of ___________, specifically designed to carry
out a single body function.
3.
A(n) ___________ is a very large molecule made by linking a series of
repeating units.
4.
A(n) ___________ is composed of a sugar molecule, a phosphorus-containing
group, and a nitrogen-containing molecule called a base.
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5.
DNA is actually a very large molecule made by linking a series of ___________
to form a natural polymer.
6.
___________ different bases are associated with the makeup of DNA.
7.
Watson and Crick demonstrated that DNA is composed of two strands coiled
into the shape of a(n) ___________.
8.
The structure of DNA requires the pairing of base A to ___________ and base
G to ___________.
9.
The base sequence T–G–C–A can be paired with the base sequence
___________ in a double-helix configuration.
10.
The inheritable traits that are controlled by DNA arise out of DNA’s ability to
direct the production of ___________.
11.
___________ are derived from a combination of up to twenty known amino
acids.
12.
The production of an amino acid is controlled by a sequence of ___________
bases on the DNA molecule.
13.
True or False: Enzymes known as DNA polymerase assemble new DNA strands
into a proper base sequence during replication. ___________
14.
True or False: DNA can be copied outside a living cell. ___________
15.
Recombinant DNA relies on the ability of chemicals known as ___________ to
cut DNA into fragments.
16.
True or False: All of the letter sequences in DNA code for the production of
proteins. ___________
17.
In RFLP DNA typing, restriction enzymes are used to cut out (repeating,
random) sequences from the DNA molecule.
18.
In RFLP DNA typing, restriction enzymes are used to cut out sequences of
DNA with different (widths, lengths).
19.
DNA fragments can be sorted according to their size by the technique of
___________.
20.
In the RFLP DNA typing process, DNA fragments are transferred to a nylon
membrane by a process called ___________ blotting.
21.
True or False: In the RFLP DNA typing process, a radioactively labeled probe
is used to visualize the separated DNA fragments. ___________
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22.
The probe complementary to the base sequence T–A–G has the letter sequence
___________.
23.
In RFLP DNA typing, a typical DNA pattern shows (two, three) bands.
24.
True or False: Specimens amenable to DNA typing are blood, semen, body
tissues, and hair. ___________
25.
Short DNA segments containing repeating sequences of three to seven bases are
called ___________.
26.
True or False: The longer the DNA strand, the less susceptible it is to
degradation. ___________
27.
The short length of STRs allows them to be replicated by ___________.
28.
The concept of (CODIS, multiplexing) involves simultaneous detection of more
than one DNA marker.
29.
DNA fragments can be separated and identified by (gas chromatography,
capillary electrophoresis).
30.
The amelogenin gene shows two bands for a (male, female) and one band for a
(male, female).
31.
Y-STR typing is useful when one is confronted with a DNA mixture containing
more than one (male, female) contributor.
32.
Mitochondrial DNA is inherited from the (mother, father).
33.
True or False: Mitochondrial DNA is more plentiful in the human cell than is
nuclear DNA. ___________
34.
(Two, Four) regions of mitochondrial DNA have been found to be highly
variable in the human population.
35.
True or False: Polymerase chain reaction is a part of the process used in the
forensic analysis of RFLP, STRs, and mitochondrial DNA. ___________
36.
The national DNA database in the United States has standardized on
___________ STRs for entry into the database.
37.
True or False: Y-STR data is normally entered into the CODIS database
collection. ___________.
38.
Small amounts of blood are best submitted to a crime laboratory in a (wet, dry)
condition.
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39.
True or False: Airtight packages make the best containers for blood-containing
evidence. ___________
40.
Whole blood collected for DNA typing purposes must be placed in a vacuum
containing the preservative ___________.
41.
A typical STR DNA type emanating from a single individual shows a (one, two,
three)-band pattern.
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