Emerging DNA Technologies — MCQs
Identical twins can be differentiated by their ________.
Best site for DNA extraction from a 2-month-old decomposed body?
For DNA extraction from blood samples, the preferred anticoagulant is:
Which of the following is used to detect abnormal gene sequences EXCEPT?
Most reliable method to identify putrefied bodies with metallic implants?
DNA fingerprinting was first used by Alec Jeffreys in a criminal case for detecting:
In a macerated baby, the ideal sample for genetic analysis is obtained from:
Which of the following techniques is used for the detection of variations in DNA sequence and gene expression?
Best sample for DNA profiling in sexual assault after 72 hours?
Two transgenic plants were genetically engineered using Recombinant DNA technology. One plant was transformed using a plasmid vector with GFP (Green Fluorescent Protein) gene and another plant was transformed with a complete Luciferase bioluminescent system (including luciferase gene and luciferin substrate availability). Which of these two plants will glow spontaneously in the dark?
Emerging DNA Technologies Indian Medical PG Practice Questions and MCQs
Question 1: Identical twins can be differentiated by their ________.
- A. Blood grouping
- B. DNA fingerprinting
- C. Age
- D. Fingerprint (Correct Answer)
Explanation: ***Fingerprint*** - Although identical twins originate from a single zygote and share nearly identical DNA, their **fingerprints** develop uniquely due to environmental factors in the womb affecting dermal ridge formation. - This results in distinct fingerprint patterns, making them a reliable identifier to differentiate between them. *Blood grouping* - Identical twins share the same **genetic makeup** and therefore have the same **blood type**. - Blood grouping cannot be used to differentiate between them. *DNA fingerprinting* - Identical twins are derived from the same zygote, resulting in nearly **identical DNA sequences**. - While extremely fine differences might exist (e.g., somatic mutations), standard **DNA fingerprinting** would show them as the same. *Age* - Identical twins are born at the same time from the same pregnancy, meaning they have the **exact same age**. - This characteristic cannot be used to differentiate between them.
Question 2: Best site for DNA extraction from a 2-month-old decomposed body?
- A. Muscle
- B. Bone
- C. Teeth (Correct Answer)
- D. Hair
Explanation: ***Teeth*** - Teeth, particularly the **pulp and dentin**, provide a highly protected environment for DNA, making them ideal for DNA extraction from **decomposed remains** due to their robust structure. - The hard enamel casing shields the internal DNA from environmental degradation and microbial contamination, allowing for excellent preservation over extended periods. - **Dental pulp** is consistently reliable and easily accessible, making teeth the **preferred first choice** in forensic DNA extraction from decomposed bodies. *Bone* - **Bone**, particularly the **petrous portion of the temporal bone** and long bones, is also an **excellent source** of DNA in decomposed remains and is widely used in forensic practice. - However, DNA extraction from bone requires more extensive processing (demineralization, grinding) compared to teeth, making it a **second-line choice** when teeth are available. - The petrous temporal bone is notably resistant to degradation, but teeth remain more practically accessible. *Muscle* - **Muscle tissue** contains significant DNA when fresh, but is highly susceptible to **autolysis and bacterial degradation** in a decomposed body. - As decomposition progresses over 2 months, muscle tissue breaks down rapidly, reducing both the quantity and quality of recoverable DNA significantly. *Hair* - **Hair shafts** primarily contain mitochondrial DNA (mtDNA) with minimal nuclear DNA, which limits their use for individual identification. - Hair roots (if present) contain nuclear DNA, but in decomposed remains, hair is often shed or degraded, making it an unreliable source compared to teeth.
Question 3: For DNA extraction from blood samples, the preferred anticoagulant is:
- A. EDTA (Correct Answer)
- B. Plain bulb
- C. Formalin
- D. None of the options
Explanation: ***EDTA*** - **EDTA** (ethylenediaminetetraacetic acid) acts as an anticoagulant by **chelating calcium ions**, which are essential for the coagulation cascade, making it ideal for DNA extraction. - Using an EDTA collection tube ensures that the blood sample remains in its liquid state, preventing clot formation which can trap DNA and make isolation difficult. *Plain bulb* - A plain bulb refers to a tube without any anticoagulant, allowing the blood to **clot naturally**. - While serum can be obtained from such a tube, the DNA would be entrapped within the clot, making its extraction **less efficient and potentially damaging**. *Formalin* - **Formalin** (a solution of formaldehyde) is a fixative used to preserve tissue morphology by **cross-linking proteins**. - While useful for histopathology, it **damages DNA** through chemical modifications and fragmentation, making it unsuitable for DNA isolation or genetic analysis. *None of the options* - This option is incorrect because **EDTA is a widely recognized and appropriate** anticoagulant for preserving DNA samples from blood for molecular studies.
Question 4: Which of the following is used to detect abnormal gene sequences EXCEPT?
- A. RFLP analysis
- B. Pyrosequencing
- C. Flow cytometry (Correct Answer)
- D. FISH
Explanation: ***Flow cytometry*** - **Flow cytometry** is primarily used to analyze **cell populations** based on their physical and biochemical characteristics (e.g., size, granularity, and protein expression) by passing them single file through a laser beam, not for direct gene sequencing. - It detects and quantifies cells labeled with **fluorescent antibodies**, making it useful for immunophenotyping, cell sorting, and DNA content analysis, but not for identifying specific gene sequences or mutations. *RFLP analysis* - **Restriction fragment length polymorphism (RFLP) analysis** detects variations in **DNA sequences** by using **restriction enzymes** to cut DNA at specific sites. - Differences in fragment lengths indicate **polymorphisms** or **mutations** within the recognition sites, thereby identifying abnormal gene sequences. *Pyrosequencing* - **Pyrosequencing** is a method of **DNA sequencing** that determines the sequence of nucleotides by detecting the release of pyrophosphate during DNA synthesis. - It is used to identify **single nucleotide polymorphisms (SNPs)** and **short genetic variations**, making it suitable for detecting abnormal gene sequences. *FISH* - **Fluorescence in situ hybridization (FISH)** uses **fluorescently labeled DNA probes** that bind to specific complementary **DNA sequences** on chromosomes. - It is a powerful cytogenetic technique for detecting **chromosomal abnormalities**, such as deletions, translocations, and amplifications, thereby identifying abnormal gene sequences.
Question 5: Most reliable method to identify putrefied bodies with metallic implants?
- A. Serial number matching (Correct Answer)
- B. X-ray superimposition
- C. Dental comparison
- D. DNA profiling
Explanation: ***Serial number matching*** - Metallic implants, such as orthopedic prostheses or pacemakers, often carry **unique serial numbers** that can be traced back to the manufacturer and patient records. - This method is highly reliable even in cases of severe **putrefaction** or fragmentation, as the implant itself is resistant to decomposition. *X-ray superimposition* - This method involves superimposing antemortem (before death) and postmortem (after death) X-rays to look for matching anatomical features. - While useful for bone and tooth identification, it is less reliable for specific identification with metallic implants compared to direct serial number matching, especially if the antemortem X-rays predate the implant. *Dental comparison* - **Dental comparison** involves comparing antemortem dental records (X-rays, charts) with postmortem dental findings. - This method is very effective for identification in general, but it does not directly utilize the metallic implant for identification and thus is not the *most reliable* method when an implant is present. *DNA profiling* - **DNA profiling** is highly effective for identification using biological samples, but it relies on obtaining viable DNA. - In cases of severe putrefaction, obtaining **high-quality, uncontaminated DNA** suitable for profiling can be very challenging or impossible from the remains themselves.
Question 6: DNA fingerprinting was first used by Alec Jeffreys in a criminal case for detecting:
- A. Immigration purpose
- B. Disputed paternity
- C. Murder
- D. Rape (Correct Answer)
Explanation: ***Rape*** - **Alec Jeffreys** first applied DNA fingerprinting in 1986 to solve the **Narborough murders case** in Leicestershire, UK. - The technique was used to analyze **semen samples** from two rape-murder victims (1983 and 1986), linking them to a single perpetrator. - The **DNA evidence from semen** (sexual assault evidence) was the key forensic material that demonstrated the power of DNA fingerprinting in criminal investigation. - This led to the conviction of **Colin Pitchfork** in 1988, marking the first use of DNA profiling to solve a criminal case. *Immigration purpose* - While DNA fingerprinting is used for immigration cases to confirm family relationships, this was **not its initial application** by Jeffreys. - Its use in immigration came later, after its breakthrough in criminal forensics. *Disputed paternity* - Paternity testing is a common application of DNA fingerprinting, but it was **not the first criminal case** where Jeffreys demonstrated its utility. - The technique's power in establishing biological relationships was recognized after its initial use in criminal investigations. *Murder* - While the Narborough case did involve murders, the question focuses on what was **detected through DNA evidence**. - The DNA profiling was performed on **semen samples** (rape evidence), not on evidence directly proving murder. - The forensic breakthrough was in linking the sexual assault evidence to the perpetrator, which then solved the murder cases.
Question 7: In a macerated baby, the ideal sample for genetic analysis is obtained from:
- A. Clotted fetal blood
- B. Placental Tissue (Correct Answer)
- C. Fibroblast from skin
- D. Fibroblast from Achilles tendon
Explanation: ***Placental Tissue*** - **Placental tissue** (chorionic villi) is preferred for genetic analysis in macerated fetuses because it is less susceptible to **autolysis** and **bacterial contamination** compared to fetal tissues. - The placenta often retains viable cells with intact DNA even when fetal tissues have significantly degraded, making it a more reliable source for **karyotyping** or **molecular genetic studies**. *Clotted fetal blood* - **Clotted fetal blood** from a macerated fetus is generally unsuitable due to significant **cellular degradation** and **DNA fragmentation** caused by autolysis. - The quality of DNA extracted from such a sample would likely be poor, leading to unreliable or unsuccessful genetic testing. *Fibroblast from skin* - While fibroblasts can be cultured from skin, obtaining a viable biopsy from a **macerated fetus** is challenging due to extensive **tissue degradation** and the high risk of **bacterial contamination**. - Successful culture and growth of fibroblasts would be unlikely given the compromised state of the fetal tissue. *Fibroblast from Achilles tendon* - Similar to skin, obtaining viable fibroblasts from the **Achilles tendon** of a macerated fetus is difficult due to widespread **autolysis** and **tissue degeneration**. - The degradation of cells in macerated fetuses significantly reduces the chances of culturing viable cells needed for genetic analysis from any fetal tissue, including tendons.
Question 8: Which of the following techniques is used for the detection of variations in DNA sequence and gene expression?
- A. Southern blot
- B. Western blot
- C. Microarray (Correct Answer)
- D. Northern blot
Explanation: ***Microarray*** - **Microarrays** are designed to detect thousands of DNA or RNA sequences simultaneously, making them ideal for analyzing **gene expression profiles** and identifying **sequence variations** like SNPs. - They involve hybridizing labeled sample DNA/RNA to probes fixed on a solid surface, with the intensity of hybridization indicating the presence or abundance of specific sequences. *Northern blot* - The **Northern blot** technique is primarily used to study **gene expression** by detecting specific **RNA sequences** in a sample. - It does not directly analyze DNA sequence variations. *Southern blot* - The **Southern blot** is a molecular biology method used to detect specific **DNA sequences** in DNA samples. - While it can identify large-scale DNA rearrangements or deletions, it is not optimized for simultaneous detection of multiple gene expression levels or subtle sequence variations. *Western blot* - The **Western blot** is used to detect specific **proteins** in a sample. - It analyzes protein expression levels and modifications and is not designed for the detection of DNA sequence variations or gene expression at the RNA level.
Question 9: Best sample for DNA profiling in sexual assault after 72 hours?
- A. Victim's clothes (Correct Answer)
- B. Cervical swab
- C. Vaginal swab
- D. Fingernail scrapings
Explanation: ***Victim's clothes*** - After 72 hours, **spermatozoa** in or on the skin are often degraded, but foreign DNA (from the perpetrator's skin cells, semen, or other bodily fluids) can persist on clothing, especially in protected areas. - Clothing acts as a **storage medium for trace evidence**, and DNA can remain viable for profiling much longer than on mucous membranes due to drying and lack of enzymatic degradation. *Cervical swab* - **Spermatozoa** typically become undetectable in the cervix within 24-48 hours, though some studies show persistence up to 72 hours. - Beyond 72 hours, the likelihood of obtaining viable **perpetrator DNA** from a cervical swab significantly decreases due to degradation and cellular turnover. *Vaginal swab* - **Spermatozoa** found in the vagina are subject to enzymatic degradation and expulsion, with viability for DNA profiling decreasing significantly after 24-48 hours. - While trace DNA might still be present, the quantity and quality for profiling are usually much lower than on clothing after such an extended period. *Fingernail scrapings* - While fingernail scrapings can yield **perpetrator DNA** if there was physical struggle, this is highly dependent on the act of scraping the assailant's skin. - It is not a guaranteed source in every sexual assault and is less likely to contain strong DNA evidence after 72 hours compared to clothing, which captures shed cells and fluids passively.
Question 10: Two transgenic plants were genetically engineered using Recombinant DNA technology. One plant was transformed using a plasmid vector with GFP (Green Fluorescent Protein) gene and another plant was transformed with a complete Luciferase bioluminescent system (including luciferase gene and luciferin substrate availability). Which of these two plants will glow spontaneously in the dark?
- A. Plant with Luciferase Gene (Correct Answer)
- B. Both plants
- C. Plant with GFP Gene
- D. None of the options
Explanation: ***Plant with Luciferase Gene*** - The plant transformed with the **complete bioluminescent system**, including the **luciferase gene** and **luciferin substrate**, will glow spontaneously because luciferase acts on luciferin to produce light through a chemical reaction. - The question explicitly states "complete Luciferase bioluminescent system (including luciferase gene and luciferin substrate availability)," indicating all necessary components for bioluminescence are present. - **Bioluminescence** is light produced by living organisms through chemical reactions, requiring both enzyme (luciferase) and substrate (luciferin). *Both plants* - This is incorrect because the plant with the **GFP gene** alone will not glow spontaneously in the dark. - GFP requires **excitation by an external light source** (e.g., UV or blue light) to fluoresce, so it cannot contribute to spontaneous glowing. - Only the luciferase-transformed plant produces light spontaneously. *Plant with GFP Gene* - **GFP** (Green Fluorescent Protein) is **fluorescent**, not bioluminescent; it absorbs light at one wavelength and emits it at another wavelength. - GFP does not generate its own light in the dark and requires **illumination with an appropriate light source** (blue or ultraviolet light) to excite the protein and produce visible fluorescence. - Without external light excitation, GFP remains invisible in darkness. *None of the options* - This is incorrect because the plant equipped with a **complete luciferase bioluminescent system** is specifically designed to produce light spontaneously. - All required components (luciferase enzyme and luciferin substrate) are present and functional, enabling autonomous light production in the dark.
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