DNA Profiling and Forensic Biology Practice Questions

Q: Which of the following tests is not used for detection of seminal stain?

Phadebas Test. ***Phadebas Test*** - The Phadebas test is primarily used for the detection and quantification of **alpha-amylase**, an enzyme found in high concentrations in saliva. - While amylase can be present in other bodily fluids, including semen, the Phadebas test is not a specific or primary method for detecting seminal stains due to its low specificity for semen compared to other methods. *Acid Phosphatase test* - The **acid phosphatase (AP) test** is a widely used presumptive test for seminal fluid due to the high concentration of **prostatic acid phosphatase** in semen. - A positive result, usually indicated by a color change, suggests the probable presence of semen, although false positives can occur. *Florence test* - The Florence test is a **confirmatory test** for the presence of **choline** in semen, which reacts with potassium iodide to form characteristic dark brown, rhombic crystals. - While historically significant, it is a less sensitive and specific test compared to modern methods. *Barbeiros test* - The Barbeiros test (or Barberio's test) is another **confirmatory chemical test** for the presence of **spermine** in semen. - Spermine reacts with picric acid to form characteristic needle-like crystals, further indicating the presence of seminal fluid.

Q: Lattes' crust test of blood stain is used to detect -

Detection of species. ***Detection species*** - **Lattes crust test** is a method used in forensic serology to determine the **species origin of a blood stain**. - It involves overlaying a crust of dried blood with **anti-sera** from different animal species to observe for agglutination, indicating a reaction and thus the species. *Nature of stain* - The **nature of the stain** typically refers to whether it is blood, semen, saliva, etc., which is usually determined through preliminary presumptive tests like the **Kastle-Meyer test** for blood. - The **Lattes crust test** specifically aims to identify the species from which the blood originated, not its general nature. *Blood group* - **Blood grouping tests** are designed to determine the ABO, Rh, or other blood types within a single species, typically humans. - While important in forensic investigations, these tests are distinct from the **Lattes crust test**, which focuses on **species identification**. *None of the options* - This option is incorrect because the **Lattes crust test** is indeed used for the **detection of species**, making option B the correct answer. - The test has a specific purpose in forensic analysis related to species identification.

Q: Which of the following methods is used for demonstrating old washed bloodstains?

Luminol spray. **Luminol spray** - **Luminol** reacts with the iron in **hemoglobin** to produce a blue-white luminescence, making it highly effective for detecting even heavily diluted or rinsed-away bloodstains. - It is particularly useful for demonstrating **old, washed-up bloodstains** at crime scenes where visual identification might be difficult. *Infrared photography* - While useful for detecting certain hidden details or substances, **infrared photography** is not the primary method for revealing old or washed-up bloodstains. - **Bloodstains** can absorb infrared light to varying degrees, but the chemical reaction of luminol is specifically designed for trace blood detection. *Magnifying lens* - A **magnifying lens** merely enhances the visibility of existing stains or patterns and cannot detect traces of blood invisible to the naked eye, particularly old or diluted ones. - It is a tool for closer inspection, not for chemical detection of hidden substances. *Ultraviolet light* - **Ultraviolet (UV) light** can be used to detect certain biological fluids such as semen or saliva, which **fluoresce** under UV. - However, fresh or old bloodstains typically *absorb* UV light rather than fluoresce, making it less effective for detecting them, especially if they are washed up.

Q: DNA fingerprinting can be done with all, except:

RBC. ***RBC*** - **Mature red blood cells** lack a nucleus and therefore do not contain **DNA**. - DNA fingerprinting relies on analyzing an individual's unique DNA sequence, which is not present in RBCs. *Saliva* - Saliva contains **epithelial cells** from the mouth, which have intact nuclei and thus sufficient DNA for analysis [2]. - It is a common and non-invasive source of DNA for forensic and genetic testing [2]. *WBC* - **White blood cells** (leukocytes) are nucleated cells that contain a full complement of DNA [2]. - They are an excellent source of DNA for genetic analysis, including DNA fingerprinting. *Spermatozoa* - **Sperm cells** are haploid and contain a nucleus with DNA, making them suitable for DNA fingerprinting [1]. - They are frequently used in forensic cases, particularly in sexual assault investigations [1].

Q: For DNA test, liquid blood is preserved in:

EDTA. ***EDTA*** - Ethylenediaminetetraacetic acid (EDTA) is the preferred anticoagulant for DNA extraction because it **chelates metal ions** (like magnesium), which are cofactors for **DNases** (enzymes that degrade DNA). - By inhibiting DNases, EDTA effectively **preserves DNA integrity** in blood samples for genetic testing. *Sodium fluoride* - **Sodium fluoride** is primarily used as an antiglycolytic agent to preserve glucose in blood samples. - It does not specifically function to preserve DNA or inhibit DNA degradation significantly. *Potassium oxalate* - **Potassium oxalate** acts as an anticoagulant by precipitating calcium, but it is not optimal for long-term DNA preservation. - Its anticoagulant properties are less suitable for molecular testing compared to EDTA, and it doesn't protect DNA as effectively. *Sodium citrate* - **Sodium citrate** is an anticoagulant primarily used for coagulation studies (e.g., PT, PTT) by chelating calcium. - While it prevents clotting, it is **less effective than EDTA** in protecting DNA from degradation by DNases, making it a poorer choice for DNA banking.

Q: Best site for DNA extraction from a 2-month-old decomposed body?

Teeth. ***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.

Q: In a forensic investigation, which technique would you use to identify the presence of seminal stains?

Acid phosphatase test. ***Acid phosphatase test*** - This is the **primary presumptive test** for screening and identifying the presence of seminal stains in forensic investigations. - Detects the enzyme **acid phosphatase**, which is present in **high concentrations in human semen** (approximately 400 times higher than in other body fluids). - A positive result, usually indicated by a **purple color change**, provides rapid preliminary identification of potential seminal stains. - This is the **preferred initial screening method** due to its sensitivity and ease of use. *Florence test* - The Florence test detects the presence of **choline**, forming characteristic **dark brown rhombic crystals** in the presence of seminal fluid. - This is a **confirmatory test** rather than a screening test, used after presumptive testing. - While specific for semen, it is not the primary method for initial identification of seminal stains. *Luminol test* - The luminol test is used to detect **bloodstains** by reacting with the iron in hemoglobin, causing **chemiluminescence** (bluish glow). - It is highly sensitive for blood but does **not identify semen** and is not used for seminal stain detection. *Barberio test* - The Barberio test detects **spermine picrate crystals**, which are specific to semen. - This is also a **confirmatory test** that requires the presence of seminal constituents. - Not used as the primary screening method for identifying the presence of seminal stains.

Q: The absorption elution technique is used for?

Detection of blood groups. ***Detection of blood groups*** - The **absorption-elution technique** is a sensitive method used to detect **ABO blood group antigens** in dried bloodstains, a common application in forensic serology. - It involves absorbing antibodies specific to blood group antigens onto the dried stain and then eluting these absorbed antibodies to react with known red blood cells. *Examination of seminal stains* - **Seminal stains** are typically examined for the presence of **spermatozoa** or markers like **prostate-specific antigen (PSA)** or **acid phosphatase**. - The absorption-elution technique is not the primary method for identifying seminal fluid or its origin. *Detection of species* - **Species identification** in forensic samples usually involves techniques such as **DNA analysis** (e.g., mitochondrial DNA sequencing) or **precipitin tests**. - The absorption-elution method is specific to blood group antigens and not generally used for broad species differentiation. *None of the options* - This option is incorrect because the **absorption-elution technique** is indeed directly applicable and commonly used for the **detection of blood groups**.

Q: Test to determine the species from a bloodstain is?

Precipitin test. ***Precipitin test*** - The **precipitin test** is a widely used serological method to determine the **species origin of a bloodstain**. - It works by detecting the presence of **species-specific proteins** (antigens) in the bloodstain through a reaction with known antibodies. *Takayama test* - The **Takayama test**, along with the Teichmann test, is a **confirmatory chemical test** used to identify blood by forming characteristic **heme crystal formations**. - It does not provide information about the **species origin** of the blood. *Benzidine test* - The **benzidine test** is a **presumptive test** for blood, meaning it indicates the *possible* presence of blood based on the peroxidase activity of hemoglobin. - It is highly sensitive but **not specific** to human blood and can react with other substances or animal blood, hence it cannot determine the species. *Teichmann's test* - **Teichmann's test** is another **confirmatory chemical test** for blood, similar to the Takayama test. - It relies on the formation of **hemin crystals** (hemochromogen crystals) and does not differentiate between human and animal blood.

Q: What is the most forensically significant information that can be detected from a dried blood stain?

Blood group. ***Blood group*** - Among the options provided, **blood group** analysis provides identifying information about the individual who deposited the blood, helping to include or exclude suspects. - However, it should be noted that **DNA profiling** (not listed as an option) is the gold standard in modern forensic practice, offering individual-specific identification with far superior discriminatory power. - Blood group typing has **limited discriminatory value** as it only classifies individuals into broad categories (A, B, AB, O) shared by millions of people. - In contemporary forensic laboratories, blood grouping has been largely superseded by **DNA analysis** from dried blood stains. *Nature of stain* - The **nature of the stain** (e.g., drip, spatter, swipe) indicates how the blood was deposited through **bloodstain pattern analysis (BPA)**. - This provides valuable information for **crime scene reconstruction** and understanding the sequence of events, but does not identify the source individual. - It's a separate forensic discipline from biological identification. *Detection species* - **Species identification** determines if the blood is human or animal, which is an important **preliminary screening test**. - This is typically done using precipitin tests or other immunological methods. - While important, it lacks **individual specificity** and only confirms the blood is human, without linking it to a particular person. *None of the options* - This option would arguably be the most accurate if we consider that **DNA profiling** is the truly most forensically significant information obtainable from dried blood stains in modern practice. - However, given the context of the options provided, blood group represents the most individualizing characteristic available among the choices listed.

Question 1

Which of the following tests is not used for detection of seminal stain?

Accepted Answer

Phadebas Test

Answer

Acid Phosphatase test

Answer

Florence test

Answer

Barbeiros test

Question 2

Lattes' crust test of blood stain is used to detect -

Accepted Answer

Detection of species

Answer

Nature of stain

Answer

Blood group

Answer

None of the options

Question 3

Which of the following methods is used for demonstrating old washed bloodstains?

Accepted Answer

Luminol spray

Answer

Infrared photography

Answer

Magnifying lens

Answer

Ultraviolet light

Question 4

DNA fingerprinting can be done with all, except:

Accepted Answer

RBC

Answer

Saliva

Answer

WBC

Answer

Spermatozoa

Question 5

For DNA test, liquid blood is preserved in:

Accepted Answer

EDTA

Answer

Sodium fluoride

Answer

Potassium oxalate

Answer

Sodium citrate

Question 6

Best site for DNA extraction from a 2-month-old decomposed body?

Accepted Answer

Teeth

Answer

Muscle

Answer

Bone

Answer

Hair

Question 7

In a forensic investigation, which technique would you use to identify the presence of seminal stains?

Accepted Answer

Acid phosphatase test

Answer

Florence test

Answer

Luminol test

Answer

Barberio test

Question 8

The absorption elution technique is used for?

Accepted Answer

Detection of blood groups

Answer

Examination of seminal stains

Answer

Detection of species

Answer

None of the options

Question 9

Test to determine the species from a bloodstain is?

Accepted Answer

Precipitin test

Answer

Takayama test

Answer

Benzidine test

Answer

Teichmann's test

Question 10

What is the most forensically significant information that can be detected from a dried blood stain?

Accepted Answer

Blood group

Answer

Nature of stain

Answer

Detection species

Answer

None of the options

DNA Profiling and Forensic Biology — MCQs

DNA Profiling and Forensic Biology — MCQs

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