DNA Forensics

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


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.



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