DNA Databases — MCQs
Doctor or nurse disclosing the identity of a rape victim is punishable under the following section of IPC?
For DNA extraction from blood samples, the preferred anticoagulant is:
DNA fingerprinting was first used by Alec Jeffreys in a criminal case for detecting:
Best sample for DNA profiling in sexual assault after 72 hours?
Best site for DNA extraction from a 2-month-old decomposed body?
Apoptosis is characterized by all of the following except which of the following?
Which base does adenine bind with in DNA?
A child was born 8 months after the father's death. The grandparents filed a case claiming that the baby is not their son's, but DNA testing confirmed paternity. What is the child called?
Which enzyme polymerises Okazaki fragments?
Which enzyme is required for cutting the DNA strand during synthesis?
DNA Databases Indian Medical PG Practice Questions and MCQs
Question 1: Doctor or nurse disclosing the identity of a rape victim is punishable under the following section of IPC?
- A. Section 224A
- B. Section 226A
- C. Section 222A
- D. Section 228A (Correct Answer)
Explanation: ***Section 228A IPC*** - This section of the Indian Penal Code specifically deals with the **disclosure of the identity of a victim of rape and certain sexual offenses** (Sections 376, 376A, 376AB, 376B, 376C, 376D, 376DA, 376DB, 376E). - Making public the name or any matter that can reveal the identity of a rape victim by **any person, including doctors and nurses**, is a punishable offense. - **Punishment**: Imprisonment up to **2 years** and fine. - **Exception**: Disclosure is permitted only to authorized persons like police officers for investigation purposes. - **Important**: This is now covered under **Section 72 of Bharatiya Nyaya Sanhita (BNS) 2023**, which replaced the IPC. *Section 224A* - This is **not a valid or recognized provision** within the Indian Penal Code. - It does not relate to offenses concerning privacy or the identity of sexual assault victims. *Section 226A* - This is **not a valid or recognized provision** within the Indian Penal Code. - It does not pertain to the confidentiality of victims of sexual offenses. *Section 222A* - This is **not a valid or recognized provision** within the Indian Penal Code. - There is no such specific section addressing disclosure of victim identity in the IPC.
Question 2: 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 3: 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 4: 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 5: 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 6: Apoptosis is characterized by all of the following except which of the following?
- A. Chromatin condensation
- B. Cell shrinkage
- C. DNA fragmentation
- D. Cell proliferation (Correct Answer)
Explanation: ***Inflammation*** - Apoptosis is a programmed cell death process that **does not induce inflammation**, contrasting with necrosis, which does [1]. - It is characterized by its **clean uptake** by surrounding cells without eliciting an immune response [1]. *DNA fragmentation* - A hallmark of apoptosis, where **DNA is cleaved** into smaller fragments as part of the intrinsic cell death pathway [2]. - This fragmentation can be detected via techniques such as **agarose gel electrophoresis**. *Cell shrinkage* - In apoptosis, cells exhibit **shrinkage**, also known as **pyknosis**, as they lose their volume and adopt a condensed morphology. - This shrinkage is due to changes in the cytoskeleton and loss of intracellular water. *Chromatin condensation* - One of the early features of apoptosis is **chromatin condensation**, which leads to the formation of dense nuclear material [3]. - This process is part of the typical morphology seen during programmed cell death. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Cellular Responses to Stress and Toxic Insults: Adaptation, Injury, and Death, pp. 67-69. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Cellular Responses to Stress and Toxic Insults: Adaptation, Injury, and Death, pp. 64-65. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 80-81.
Question 7: Which base does adenine bind with in DNA?
- A. Thymine (Correct Answer)
- B. Guanine
- C. Cytosine
- D. Uracil
Explanation: ***Thymine*** - In a **DNA double helix**, **adenine (A)** forms **two hydrogen bonds** exclusively with **thymine (T)**. - This specific pairing is known as **Chargaff's rules** and is fundamental to the structure and stability of DNA. *Guanine* - **Guanine (G)** specifically pairs with **cytosine (C)** in DNA and RNA, forming **three hydrogen bonds**. - Its structure and hydrogen bonding properties are incompatible with a stable pairing with adenine. *Cytosine* - **Cytosine (C)** exclusively pairs with **guanine (G)** in both DNA and RNA, through **three hydrogen bonds**. - This pairing is essential for the stability and integrity of the nucleic acid double helix. *Uracil* - **Uracil (U)** is found in **RNA**, where it replaces thymine and pairs with **adenine (A)**. - It is not present in DNA under normal physiological conditions.
Question 8: A child was born 8 months after the father's death. The grandparents filed a case claiming that the baby is not their son's, but DNA testing confirmed paternity. What is the child called?
- A. Suppositious child
- B. Fabricated child
- C. Posthumous child (Correct Answer)
- D. Illegitimate child
Explanation: ***Posthumous child*** - A **posthumous child** is one born after the death of its father. - In most legal systems, such a child is considered an heir and has rights equivalent to those born before the father's death, especially after paternity is confirmed. *Suppositious child* - A **suppositious child** is one who is falsely substituted for another, typically with the intent to defraud or claim an inheritance under false pretenses. - This term does not apply here as paternity was confirmed by DNA testing, indicating the child is genuinely linked to the deceased father. *Fabricated child* - The term **fabricated child** implies the child does not exist or was created through fraudulent means, often in the context of false claims or elaborate schemes. - In this scenario, the child is real and paternity has been verified, making "fabricated" an inaccurate description. *Illegitimate child* - An **illegitimate child** is historically defined as one born outside of marriage between its biological parents. - While the father died before the child's birth, the question does not provide information about the parents' marital status, and the term primarily refers to marital legality rather than the circumstances of the father's death.
Question 9: Which enzyme polymerises Okazaki fragments?
- A. DNA polymerase I
- B. DNA polymerase II
- C. DNA polymerase III (Correct Answer)
- D. RNA polymerase
Explanation: ***DNA polymerase III*** - **DNA polymerase III** is the primary replicative enzyme in **prokaryotes (bacteria)** responsible for synthesizing new DNA strands, including the **polymerization of Okazaki fragments** on the lagging strand. - It possesses high processivity (can add ~500 nucleotides without dissociating), essential for rapid and efficient DNA synthesis during replication, adding nucleotides in a **5' to 3' direction**. - In **eukaryotes**, DNA polymerase δ (delta) performs the analogous function of polymerizing Okazaki fragments. *DNA polymerase I* - **DNA polymerase I** in prokaryotes primarily functions in **removing RNA primers** left by primase and **filling the resulting gaps** with DNA nucleotides. - It has 5' to 3' exonuclease activity for primer removal and polymerase activity for gap filling, but is **not the main enzyme for elongating Okazaki fragments**. - Its role is in **DNA repair and finishing replication**, not the extensive synthesis of Okazaki fragments. *DNA polymerase II* - **DNA polymerase II** in prokaryotes is primarily involved in **DNA repair mechanisms**, particularly in **restarting stalled replication forks** and responding to DNA damage. - It is not the main enzyme responsible for the polymerization of **Okazaki fragments** during normal DNA replication. *RNA polymerase* - **RNA polymerase** (specifically **primase**, a specialized RNA polymerase) synthesizes short **RNA primers** (8-12 nucleotides) during DNA replication, which provide the 3'-OH group necessary to initiate DNA synthesis. - It does not synthesize DNA or polymerize **Okazaki fragments**; its function is to create RNA primers, not extend DNA strands.
Question 10: Which enzyme is required for cutting the DNA strand during synthesis?
- A. DNA polymerase
- B. DNA ligase
- C. Topoisomerase (Correct Answer)
- D. Helicase
Explanation: ***Topoisomerase*** - **Topoisomerases** are enzymes essential for DNA replication; they induce temporary **single- or double-strand breaks** in DNA to relieve **supercoiling** ahead of the replication fork. - This cutting and rejoining activity prevents the DNA from becoming excessively tangled and facilitates the unwinding process required for synthesis. *DNA polymerase* - **DNA polymerase** is responsible for **synthesizing new DNA strands** by adding nucleotides, not for cutting the DNA backbone. - It works by moving along the template strand, reading the bases, and then adding complementary nucleotides to the growing DNA strand. *DNA ligase* - **DNA ligase** functions to **join DNA fragments** together by forming phosphodiester bonds, especially in sealing Okazaki fragments during lagging strand synthesis. - Its role is to ligate (join) cut strands, not to initiate cuts in the DNA. *Helicase* - **Helicase** unwinds the DNA double helix into single strands using ATP hydrolysis; it **separates the two strands** but does not cut the phosphodiester backbone. - This enzyme creates the replication fork by disrupting hydrogen bonds between base pairs, making the DNA accessible for replication machinery.
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