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.

Q: Which of the following is the best method for paternity testing?

Microsatellite analysis. **Explanation:** **Microsatellite analysis**, also known as **Short Tandem Repeat (STR) analysis**, is the gold standard for paternity testing. STRs are small sequences of DNA (2–6 base pairs) that repeat multiple times at specific loci. Because the number of repeats is highly polymorphic (variable) among individuals and inherited in a Mendelian fashion (50% from each parent), comparing these loci provides a "DNA fingerprint" with a probability of paternity often exceeding 99.99%. **Analysis of Incorrect Options:** * **Karyotyping (A):** This involves visualizing the entire set of chromosomes to detect numerical or structural abnormalities (e.g., Trisomy 21). It lacks the resolution to distinguish between individuals for parentage, as all healthy humans have the same basic karyotype (46,XX or 46,XY). * **Northern blot analysis (C):** This technique is used to study **RNA** expression levels, not DNA. Since paternity is based on inherited genomic DNA, RNA analysis is irrelevant for this purpose. * **All of the above (D):** Incorrect, as only STR analysis provides the necessary genetic resolution for individual identification. **High-Yield Facts for NEET-PG:** * **CODIS (Combined DNA Index System):** The standard database uses 13–20 core STR loci for forensic identification. * **Mitochondrial DNA (mtDNA):** Useful for tracing **maternal** lineage only (all children of one mother have identical mtDNA). * **Y-STR Analysis:** Useful for tracing **paternal** lineage in male offspring. * **RFLP (Restriction Fragment Length Polymorphism):** The older method of DNA profiling; it is accurate but requires large samples of undegraded DNA, making STR (which uses PCR) the modern preference.

Q: What is the most informative test for parental identification?

DNA fingerprinting. **Explanation:** **DNA Fingerprinting (DNA Profiling)** is the gold standard and most informative test for parental identification because it analyzes specific regions of DNA called **Short Tandem Repeats (STRs)** or Variable Number Tandem Repeats (VNTRs). Since an individual inherits exactly 50% of their nuclear DNA from each biological parent, comparing these genetic markers provides a statistical certainty of over 99.9% for inclusion and 100% for exclusion of paternity/maternity. **Analysis of Incorrect Options:** * **Human Leukocyte Antigen (HLA):** While HLA typing was used historically for paternity testing, it is significantly less specific than DNA profiling. It relies on protein markers on white blood cells, which have limited polymorphism compared to the vast variability found in non-coding DNA. * **Parental Likeness Assessment:** This is a subjective, phenotypic observation (e.g., facial features, eye color). It is scientifically unreliable and inadmissible as primary evidence in modern forensics due to the complexities of polygenic inheritance and environmental factors. * **Assessment of Developmental Defects:** Congenital anomalies or hereditary defects are not unique identifiers. While they may suggest a genetic link, they do not provide the definitive molecular proof required for legal parental identification. **High-Yield Facts for NEET-PG:** * **Alec Jeffreys (1984):** Developed the first DNA fingerprinting technique. * **Lalji Singh:** Known as the "Father of Indian DNA Fingerprinting." * **Specimen of Choice:** Blood (EDTA) is preferred, but any nucleated cell (semen, hair follicle, buccal swab) can be used. * **Mitochondrial DNA (mtDNA):** Used specifically for maternal lineage (matrilineal inheritance) as it is passed only from the mother to all her children. * **Y-STR Analysis:** Used to trace paternal lineage (patrilineal inheritance) in male offspring.

Q: DNA fingerprinting is based on which characteristic of DNA?

Variable number tandem repeats. **Explanation:** **DNA Fingerprinting** (also known as DNA profiling) is a technique used to identify individuals by analyzing specific regions of their genome. The correct answer is **Variable Number Tandem Repeats (VNTRs)**. 1. **Why VNTRs are correct:** Human DNA contains non-coding regions called "satellite DNA" where short nucleotide sequences are repeated many times. The number of these repeats varies significantly between individuals (except identical twins), making them highly polymorphic. These are called VNTRs (a type of Minisatellite). Because every person inherits a unique combination of repeat lengths from their parents, they serve as a genetic "barcode" for identification. 2. **Why other options are incorrect:** * **Constant tandem repeats:** If the number of repeats were constant among all humans, it would be impossible to distinguish one individual from another. * **Non-repetitive sequences:** Most of the functional genome consists of non-repetitive sequences (genes). These are highly conserved (similar) across the human species to ensure proper protein function and lack the variation needed for individual identification. * **Exons:** These are the coding regions of DNA. Like non-repetitive sequences, exons are generally conserved to maintain biological function and do not provide the polymorphism required for forensic profiling. **High-Yield Facts for NEET-PG:** * **Father of DNA Fingerprinting:** Sir Alec Jeffreys (developed the technique in 1984). * **Father of DNA Fingerprinting in India:** Dr. Lalji Singh. * **Modern Technique:** Current forensics primarily uses **STRs (Short Tandem Repeats)** or Microsatellites, which are shorter than VNTRs and easier to amplify via PCR. * **Specimen of Choice:** Any nucleated cell (Blood/WBCs, semen, hair follicle, skin, or bone marrow). Mature RBCs cannot be used as they lack a nucleus.

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

Question 6

Which of the following is the best method for paternity testing?

Accepted Answer

Microsatellite analysis

Answer

Karyotyping

Answer

Northern blot analysis

Answer

All of the above

Question 7

What is the purpose of using a dried blood stain's crust in forensic analysis?

Accepted Answer

Determination of the blood group

Answer

Detection of the species of origin

Answer

Determination of secretor status

Answer

Characterization of the nature of the stain

Question 8

What is the most informative test for parental identification?

Accepted Answer

DNA fingerprinting

Answer

Human Leukocyte Antigen (HLA)

Answer

Parental likeness assessment

Answer

Assessment of developmental defects

Question 9

DNA fingerprinting is based on which characteristic of DNA?

Accepted Answer

Variable number tandem repeats

Answer

Constant tandem repeats

Answer

Non-repetitive sequences

Answer

Exons

Question 10

Chimeric DNA is used for what purpose?

Accepted Answer

Organ transplantation

Answer

Paternity testing

Answer

Maternity testing

Answer

Personal identification

DNA Profiling and Forensic Biology — MCQs

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