DNA
Forensic Quiz Crafted by-
Mr.
Arun Ghuge
Head
& Asst. Professor
M.E.S.
Group-A (Gazetted)
Department
of Forensic Biology,
Government
Institute of Forensic Science,
Aurangabad,
M.H, India.
Introduction to DNA forensics
Forensic
scientists can use DNA profiles to identify criminals or determine parentage.
A DNA profile is like a genetic fingerprint. Every person has a
unique DNA profile, making it very useful for identifying people involved in a
crime. The only exception to this is identical twins. The results from DNA
profiles may be used in court. For example, the samples collected from a crime
scene might match the DNA of a suspect. This could be used as evidence that the
suspect had been present at the crime scene but it does not necessarily prove
that the suspect committed the crime. A DNA profile can tell the scientist if
the DNA is from a man or woman, and if the sample being tested belongs to a
particular person. DNA profiling is
the process where a specific DNA pattern, called a profile, is obtained from a
person or sample of bodily tissue. Even though we are all unique, most of our
DNA is actually identical to other people’s DNA.
DNA
profiling is used to:
1. Identify the probable origin of a body fluid sample
associated with a crime or crime scene
2. Reveal family relationships
3. Identify disaster victims, etc
Here is the List of Questions with Answers along with explanation
Ques 1. DNA can be
extracted from
a. Hair
b. Blood
c. Semen
d.
All of the above
Answer - (d) All of the above
Explanation – DNA, or
deoxyribonucleic acid, is the fundamental building block for an individual's
entire genetic makeup. It is a component of virtually every cell in the human
body. Further, a person's DNA is the same in every cell. For example, the DNA
in a man's blood is the same as the DNA in his skin cells, semen, and
saliva. DNA is contained in blood, semen, skin cells, tissue, organs,
muscle, brain cells, bone, teeth, hair, saliva, mucus, perspiration,
fingernails, urine, feces, etc. DNA is a powerful tool because each person's
DNA is different from every other individual's, except for identical twins.
Because of that difference, DNA collected from a crime scene can either link a
suspect to the evidence or eliminate a suspect, similar to the use of
fingerprints. It also can identify a victim through DNA from relatives, even
when no body can be found. And when evidence from one crime scene is compared
with evidence from another, those crime scenes can be linked to the same
perpetrator locally, statewide, and across the Nation.
Ques 2. Hair shaft is the
source of_ _ _ _ _DNA
a. Nuclear
b. Mitochondrial
c. Plasmid
d. Chloroplast
Answer - (b) Mitochondrial
Explanation –Since there
are multiple copies of mtDNA in each mitochondrion (hundreds of mitochondria
and thousands of copies of mtDNA in each cell, compared to two copies of
nucDNA) (6,7), the presence of mitochondria in the hair shaft serve as a rich
source of mtDNA.
Ques 3. Disulfide
bridges are more in _ _ _ _ _cells
a. Sperm
b. RBC
c. WBC
d. Saliva
Answer - (a) Sperm
Explanation –During
epididymal maturation, mammalian protamines undergo a thiol oxidation to first
form intra- followed by intermolecular disulfide bonds. The covalent
sulfur-sulfur (S-S) bonds stabilize the sperm DNA and are thought crucial to
condense the mammalian sperm nucleus into its fully mature state.
Ques 4. EtBr
stands for_ _ _ _ _
a. Ethidium
bromide
b. Ethanol bromine
c. Ethidium brown
d. All of the above
Answer - (a) Ethidium bromide
Explanation - Ethidium
bromide is commonly used as a non-radioactive marker for identifying and
visualizing nucleic acid bands in electrophoresis. It fluoresces readily
with a reddish-brown color when exposed to ultraviolet light, intensifying
almost 20-fold after binding to DNA. Because ethidium bromide can bind
with DNA, it is highly toxic as a mutagen. It may potentially
cause carcinogenic or teratogenic effects, although no scientific evidence
showing either health effect has been found. Exposure routes of ethidium
bromide are inhalation, ingestion, and skin absorption. An acute
exposure to ethidium bromide causes irritation of the mouth, upper respiratory
tract, skin, and eyes.
Ques 5. In DNA extraction EDTA
act as a_ _ _ _ _
a.
Chelating agent
b. Oxidizing agent
c. Reducing agent
d. Indicator
Answer - (a) Chelating agent
Explanation –The EDTA works
as a chelating agent in the DNA extraction. It chelates the metal ion present
into the enzymes and as we all know that the metal ions are the cofactor which
increases the activity of the enzyme. By chelating the metal ions, it
deactivates the enzyme, therefore, reduces the activity of DNase and RNase.
Ques 6. SDS
stands for_ _ _ _ _
a. Sodium
dodecyl sulfate
b. Sodium dodecyl
sulfur
c. Sodium dodecyl
saturate
d. Sodium dodecyl
sulfuric acid
Answer – (a) Sodium dodecyl sulfate
Explanation - Sodium dodecyl sulfate (SDS) or sodium lauryl sulfate (SLS), sometimes
written sodium laurilsulfate, is a synthetic organic compound with the formula CH3(CH2)11SO4Na. It is an anionic surfactant used in many cleaning and
hygiene products. This molecule is an organosulfate and a salt.
Ques 7. SDS
is_ _ _ _ _
a. Anionic
detergent
b. Cationic detergent
c. Surfactant
d. None of the above
Answer - (a) Anionic detergent
Explanation - Sodium
dodecyl sulfate (SDS) binds specifically to a pre-formed internal cavity in
horse-spleen apoferritin. Although sodium dodecyl sulfate (SDS) is widely used
as an anionic detergent, it can also exert specific pharmacological
effects that are independent of the surfactant properties of the
molecule.
Ques 8. Which
one of the following is not DNA extraction method
a. Chelex
b. FTA
c. Amylase
d. Phenol chloroform
Answer - (c) Amylase
Explanation
- Different types of DNA extraction methods are available for different
cell types. For example, the DNA extraction method for plant DNA is different
from that of the blood. The first DNA extraction
attempt had performed by Friedrich Miescher in 1869.The
phenol-chloroform isoamyl alcohol method which is most popular in recent days
was developed by Joseph Sambrook and David W. Russell.
Ques 9. In FT DNA extraction method
FTA stands for
a. Flinders technology of associate
b. Flinders technology of arrangement
c. Flinders technology of amendment
d. Flinders technology of
agreement
Answer - (d) Flinders technology of agreement
Explanation – FTA
(Flinders Technology Associates) cards are cotton-Based, cellulose paper
containing chemicals that burst cells, Denature proteins and protect DNA,
leaving a sample suitable for molecular identification without the risk of
disease contamination. They are a user-friendly way to send samples from the
field to the laboratory for the identification of avian pathogens or biological
analysis.
Ques 10. The role of phenol in solvent-solvent DNA
extraction method is
a. Protein
solubilisation
b. Lipid
solubilisation
c. carbohydrate
solubilisation
d. calcium
solubilisation
Answer - (a) Protein solubilisation
Explanation –Phenol
extraction is a commonly used method for removing proteins from a DNA sample,
e.g. to remove proteins from cell lysate during genomic DNA preparation.
How the procedure is
performed. First, a volume of phenol is added to the aqueous soup containing
the proteins and the DNA to be purified.
Since phenol and water are
immiscible, two phases form: a water (a.k.a. aqueous) phase and a phenol phase.
Phenol is the more dense of the two liquids so it sits on the bottom.
The phases are then mixed
thoroughly. This forces the phenol into the water layer where it forms an
emulsion of droplets throughout. The proteins in the water phase are denatured
and partition into the phenol, while the DNA stays in the water.
Then, the mixture is
centrifuged and the phases separate. The DNA containing water phase can now be
pipetted off and the phenol/protein solution is discarded. Commonly, the DNA is
then de-salted and concentrated using ethanol precipitation.
Ques 11. EDTA
helps in DNA extraction to inactivates
a. DNases
b. RNases
c. Protein
d. Lipids
Answer - (a) DNases
Explanation – TE
buffer is also called as T10E1 Buffer, and read as “T ten E one buffer”. To
make a 100 ml solution of T10E1 Buffer, 1 ml of 1 M Tris base (pH 10-11) and
0.2 ml EDTA (0.5 M) are mixed and made up with double distilled water up to
100ml. Add microliter amounts of high molarity HCl to lower the pH to 8.
Based on nuclease studies
from the 1980s, the pH is usually adjusted to 7.5 for RNA and 8.0 for
DNA.[citation needed] The respective DNA and RNA nucleases are supposed to be
less active at these pH values, but pH 8.0 can safely be used for storage of
both DNA and RNA.
EDTA further inactivates
DNase, by binding to metal cations required by this enzyme.
Ques 12. The
main source of the DNA in blood is
a. RBC
b. WBC
c. Platelet
d. All of the above
Answer - (b) WBC
Explanation –The two
primary sources of human DNA that have been used in genetic analysis studies
are white blood cells and cheek cells from saliva, mouthwash or swabs. Blood is
an excellent source of human DNA. DNA is present in white blood cells of humans,
but not red blood cells which lack nuclei.
Ques 13. DTT in hair DNA extraction breaks_ _ _ _
a. Disulphide bond
b. Hydrogen bond
c. Hydrophobic bond
d. Covalent bond
Answer - (a) Disulphide bond
Explanation –DTT is used as
a reducing or “deprotecting” agent for thiolated DNA. … DTT is frequently used
to reduce the disulfide bonds of proteins and, more generally, to prevent
intramolecular and intermolecular disulfide bonds from forming between cysteine
residues of proteins.
Ques 14. _ _ _ _ _chemical
in DNA extraction used for disulfide bond breaking.
a. DTT
b. B-Mercaptoethanol
c. Both a and b
d. None of the above
Answer - (c) Both a and b
Explanation –Both BME and
DTT are reducing agents that inactivate disulfide bonds in ribonucleases.
Therefore, they are equivalent.
Ques 15. Precipitating
reagent in DNA extraction is
a. Ethanol
b. Methanol
c. Isopropanol
d. Both a and c
Answer - (d) Both a and c
Explanation –If the DNA
concentration in the sample is low, isopropanol may work better than ethanol to
precipitate the available proteins. In addition, isopropanol is often used for
precipitating DNA from large volumes as less alcohol is used.
Ques 16. The role of the salt in
ethanol precipitation of DNA is_ _ _ _ _
a. Neutralize the charges
on sugar phosphate backbone
b. Neutralize the charges
on sugar
c. Neutralize the
charges of adenine and guanine
d. Neutralize the
charges on thymine and cytosine
Answer - (a) Neutralize the charges on sugar phosphate backbone
Explanation –The role of
the salt in the protocol is to neutralize the charges on the sugar phosphate
backbone. A commonly used salt is sodium acetate. In solution, sodium acetate
breaks up into Na+ and [CH3COO].
Ques 17. All of the
followings are commonly used DNA extraction processes exclude
a. FTA
b. Organic
c. Chelex
d. None of the above
Answer - (d) None of the above
Explanation – There
are 3 basic steps involved in DNA extraction, that is, lysis, precipitation and
purification. In lysis, the nucleus and the cell are broken open, thus
releasing DNA. This process involves mechanical disruption and uses enzymes and
detergents like Proteinase K to dissolve the cellular proteins and free DNA.
The other step, which is
known as precipitation, separates the freed DNA from the cellular debris. It
involves use of sodium (Na+) ions to neutralize any negative charge in DNA
molecules, making them less water soluble and more stable. Alcohol (e.g
isopropanol or ethanol) is then added, causes precipitation of DNA from the
aqueous solution since it does not dissolve in alcohol.
After separation of DNA
from aqueous solution, it is then rinsed with alcohol, a process known as
purification. Purification removes all the remaining cellular debris and
unwanted material. Once the DNA is completely purified, it is usually dissolved
in water again for convenient storage and handling.
Ques 18. FTA paper was developed
by_ _ _ _ _ at Flinders University in Australia
a. Lee Burgoyne
b. Watson
c. Crick
d. Mendel
Answer - (a) Lee Burgoyne
Explanation - FTA
Paper was developed by Lee Burgoyne at Flinders University in
Australia and is a method of storing DNA. It is an absorbent
cellulose-based paper containing chemical substances to protect the
DNA from nuclease degradation and preserve the paper and DNA from
bacterial growth.
Ques 19. Following are
solid phase DNA extraction methods except
a. DNA
IQ
b.
Qiagen columns
c. Prep
Filer
d.
Phenol chloroform
Answer - (d) Phenol chloroform
Explanation –Some of the
most common DNA extraction methods include organic extraction, Chelex
extraction, and solid phase extraction.
Solid phase extraction such
as using a spin-column based extraction method takes advantage of the fact that
DNA binds to silica. The sample containing DNA is added to a column containing
a silica gel or silica beads and chaotropic salts.
The chaotropic salts disrupt
the hydrogen bonding between strands and facilitate binding of the DNA to
silica by causing the nucleic acids to become hydrophobic. This exposes the
phosphate residues so they are available for adsorption. The DNA binds to the
silica, while the rest of the solution is washed out using ethanol to remove
chaotropic salts and other unnecessary constituents.
The DNA can then be
rehydrated with aqueous low salt solutions allowing for elution of the DNA from
the beads. This method yields high-quality, largely double-stranded DNA which
can be used for both PCR and RFLP analysis.
Phenol–chloroform
extraction is a liquid-liquid extraction technique in molecular biology used to
separate nucleic acids from proteins and lipids.
Ques 20. Differential extraction
is the modified method of organic DNA extraction which separates_ _ _ _ _
a. Epithelial and sperm cell
b.
Epithelial and kidney cell
c. Salivary
and kupfer cell
d. Epithelial
and endothelial cell
Answer - (a) Epithelial and sperm cell
Explanation –Differential
extraction is a modified extraction technique allowing for the selective lysis
and isolation of DNA from a mixture of sperm and epithelial cells.
Forensic
samples, such as those from sexual assault kits, may contain male sperm cells mixed
with male and female epithelial cells.