DNA Profiling and Forensic Biology Practice Questions

Q: Which among the following is the best sample for DNA in advanced burnt dead body?

Femur. ***Femur*** - The **femur** is a large, dense, long bone that provides significant protection to the embedded **marrow** and **osteocytes** from high-heat damage. - It is currently recognized as the **gold standard** sample for DNA extraction in decomposed, skeletonized, or severely **burnt remains** due to its resistance to thermal degradation. *Spleen* - The **spleen** is a soft tissue organ that undergoes rapid putrefaction and decomposes early after death. - It is highly susceptible to heat damage in burnt bodies and is generally unsuitable for **DNA isolation** once soft tissues are compromised. *Enamel* - Although **enamel** is high in mineral content and can withstand extreme temperatures, it is almost entirely acellular and contains negligible amounts of **genomic DNA**. - While teeth (especially the **pulp chamber**) can provide good DNA, the enamel surface itself is not the source of DNA. *Sternum* - The **sternum** is a cancellous, porous bone that is more susceptible to thermal destruction compared to the thick, cortical structure of the long bones. - It is often prioritized for **bone marrow** collection in fresh bodies, but it does not offer the same protection against fire as the dense, cortical bone of the **femur**.

Q: DNA matching used for identification and comparison among family members is based on analysis of which genetic marker?

Short tandem repeats (STRs). ***Short tandem repeats (STRs)*** - These are polymorphic DNA sequences consisting of **short nucleotide sequences** (typically 2-6 base pairs) repeated in tandem, making them highly variable and ideal for **individual identification**. - Because they are highly polymorphic, they provide high **discriminatory power** required for distinguishing between individuals and determining familial relationships via inheritance patterns. *Single nucleotide polymorphisms (SNPs)* - While useful for gene mapping and ancestry studies, SNPs are **bi-allelic markers** (only two possible variations), offering less discriminatory power per locus than STRs. - They are typically used for specific trait analysis or large-scale genome-wide studies rather than the standard **commercial forensic profiling** protocols used for identification. *Ribosomal RNA genes* - These genes are highly **conserved** across species and individuals, evolved to maintain essential protein synthesis functions. - Due to their high conservation, they lack the **variability** necessary for forensic identification or distinguishing between specific individuals. *Mitochondrial DNA* - Mitochondrial DNA is inherited exclusively through the **maternal lineage**, making it incapable of distinguishing between maternal relatives. - It has a much lower **power of discrimination** compared to nuclear DNA (like STRs) because it represents a single, non-recombining haplotype shared by all maternally related individuals.

Q: Absolute proof of monozygosity is determined by?

DNA fingerprinting. **Explanation:** **1. Why DNA Fingerprinting is Correct:** DNA fingerprinting (DNA profiling) is the gold standard and absolute proof for determining monozygosity. Monozygotic (identical) twins originate from a single fertilized ovum (zygote) that splits into two. Consequently, they possess an identical genetic makeup. DNA fingerprinting analyzes highly variable regions of DNA (STRs/VNTRs); since monozygotic twins share 100% of their genetic material, their DNA profiles are identical, providing definitive proof. **2. Why Other Options are Incorrect:** * **Intervening membrane layers:** While a monochorionic placenta strongly suggests monozygosity, about 25-30% of monozygotic twins are dichorionic (if the split occurs within 3 days of fertilization). Therefore, membrane configuration is suggestive but not absolute proof. * **Sex of the babies:** While monozygotic twins are always the same sex, dizygotic (fraternal) twins can also be the same sex. Thus, sex alone cannot differentiate between the two types. * **Reciprocal skin grafting:** Historically, successful cross-grafting (no rejection) was used to indicate monozygosity because identical twins share the same HLA antigens. However, this is an invasive, outdated clinical test and is no longer considered the "absolute proof" in the era of molecular genetics. **High-Yield Facts for NEET-PG:** * **Superfecundation:** Fertilization of two ova within the same menstrual cycle by sperm from separate acts of coitus (can be different fathers). * **Superfetation:** Fertilization of two ova in different menstrual cycles (rare in humans). * **Dermatoglyphics:** Fingerprint patterns in monozygotic twins are **similar but not identical** due to intrauterine environmental factors; therefore, fingerprints cannot be used to prove monozygosity, but DNA can. * **Mixed Dentition:** Like fingerprints, dental patterns show similarities but are not identical in monozygotic twins.

Q: What is a confirmatory test for species of origin?

Ouchterlony Test. ### Explanation The **Ouchterlony Test** (Double Immunodiffusion) is the gold standard confirmatory test for determining the **species of origin** in forensic biology. **1. Why Ouchterlony Test is Correct:** When a biological sample (like a bloodstain) is found at a crime scene, forensic experts must determine if it is human or animal. The Ouchterlony test uses the principle of **antigen-antibody reaction** in an agar gel. An extract of the unknown sample (antigen) and specific anti-sera (antibodies, e.g., anti-human serum) are placed in separate wells. If the sample belongs to that species, the antigens and antibodies diffuse toward each other, meeting to form a visible **precipitin line**. This confirms the species identity with high specificity. **2. Analysis of Incorrect Options:** * **A. Origin Test:** This is a generic term and not a specific forensic laboratory technique. * **C. Olympus Test:** This is a distractor; Olympus is a well-known brand of microscopes and optical equipment, not a serological test. * **D. SOO Test:** This is an invented acronym (likely standing for "Species of Origin") used to confuse candidates; no such standardized test exists in forensic practice. **3. High-Yield Clinical Pearls for NEET-PG:** * **Precipitin Test:** The broader category of tests for species origin; Ouchterlony is the most common variant. * **Kastle-Meyer Test:** A common screening (presumptive) test for the *presence* of blood (turns pink), but it does not determine species. * **Teichmann and Takayama Tests:** Confirmatory tests for the *presence* of blood (crystal tests), not species. * **Species Identification:** Essential in hit-and-run cases or animal poaching investigations to differentiate human blood from animal blood.

Question 1

Which among the following is the best sample for DNA in advanced burnt dead body?

Accepted Answer

Femur

Answer

Spleen

Answer

Enamel

Answer

Sternum

Question 2

DNA matching used for identification and comparison among family members is based on analysis of which genetic marker?

Accepted Answer

Short tandem repeats (STRs)

Answer

Single nucleotide polymorphisms (SNPs)

Answer

Ribosomal RNA genes

Answer

Mitochondrial DNA

Question 3

What is the underlying principle of using mitochondrial DNA rather than nuclear DNA for identification in severely degraded disaster victim remains?

Accepted Answer

Mitochondrial DNA is present in thousands of copies per cell making it more likely to be recovered

Answer

Mitochondrial DNA is more specific for individual identification

Answer

Mitochondrial DNA is not affected by environmental factors

Answer

Mitochondrial DNA analysis is less expensive and faster

Question 4

Absolute proof of monozygosity is determined by?

Accepted Answer

DNA fingerprinting

Answer

Intervening membrane layers

Answer

Sex of the babies

Answer

Reciprocal skin grafting

Question 5

What is a confirmatory test for species of origin?

Accepted Answer

Ouchterlony Test

Answer

Origin Test

Answer

Olympus Test

Answer

SOO Test

DNA Profiling and Forensic Biology — MCQs

DNA Profiling and Forensic Biology — MCQs

On this page

Practice by Chapter

Want unlimited practice?