Molecular Pathology Practice Questions

Q: What is the total number of somatic chromosomes in a normal human diploid cell?

44. **Explanation:** The human genome consists of a total of **46 chromosomes**, which are organized into 23 pairs [1]. These are categorized into two types: **Autosomes (Somatic Chromosomes)** and **Allosomes (Sex Chromosomes).** 1. **The Correct Answer (D):** In a normal human diploid cell, there are **22 pairs of autosomes**, totaling **44 somatic chromosomes** [1]. These chromosomes carry genes for general body characteristics and are identical in both males and females. 2. **The Remaining 2:** The final pair (the 23rd pair) consists of sex chromosomes (XX in females or XY in males), which determine the biological sex of the individual [1]. Therefore, the formula is: **44 Autosomes + 2 Sex Chromosomes = 46 Total Chromosomes.** **Analysis of Incorrect Options:** * **Options A (42) & B (41):** These numbers do not correspond to any standard physiological or common pathological chromosomal count in humans. * **Option C (46):** This represents the **total** number of chromosomes (diploid number/2n). The question specifically asks for "somatic chromosomes" (autosomes), excluding the sex chromosomes. **Clinical Pearls for NEET-PG:** * **Euploidy:** A state where the chromosome number is an exact multiple of the haploid set (e.g., 46, 69, 92). * **Aneuploidy:** An abnormal number of chromosomes that is not a multiple of 23 (e.g., Trisomy 21/Down Syndrome has 47 chromosomes) [2]. * **Barr Body:** In females, one of the two X chromosomes is inactivated and stays as condensed heterochromatin (Barr body). The number of Barr bodies is always **(Total X chromosomes - 1)**. * **Karyotyping:** Usually performed during **Metaphase** of mitosis when chromosomes are most condensed [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 167-168. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 170-171.

Q: Which antinuclear antibody is specific for Systemic Lupus Erythematosus (SLE)?

Anti ds DNA. **Explanation:** In Systemic Lupus Erythematosus (SLE), the production of autoantibodies against nuclear antigens is the hallmark of the disease [1]. **Why Anti-dsDNA is correct:** While many antibodies appear in SLE, **Anti-dsDNA** and **Anti-Smith (Sm)** antibodies are considered **highly specific** for the diagnosis [1]. Anti-dsDNA levels often correlate with disease activity, particularly the development of lupus nephritis, making it useful for both diagnosis and monitoring. **Analysis of Incorrect Options:** * **Anti-nuclear antibodies (ANA):** This is the **best screening test** for SLE due to its very high sensitivity (95-99%) [1]. However, it lacks specificity as it is positive in many other autoimmune conditions (Scleroderma, RA, Sjögren’s) and even in healthy individuals [1]. * **Anti-centromere antibody:** This is highly specific for **Limited Cutaneous Systemic Sclerosis** (formerly CREST syndrome), not SLE [1]. * **Anti-histone antibody:** This is the characteristic marker for **Drug-Induced Lupus (DILE)** [1]. While it can be present in systemic SLE, its presence in the absence of other SLE-specific markers strongly suggests a drug-induced etiology (e.g., Hydralazine, Procainamide). **NEET-PG High-Yield Pearls:** * **Most Sensitive Test for SLE:** ANA (Indirect Immunofluorescence is the gold standard). * **Most Specific Tests for SLE:** Anti-dsDNA and Anti-Smith. * **Antibody for Neonatal Lupus/Congenital Heart Block:** Anti-Ro (SSA) and Anti-La (SSB). * **Antibody for Libman-Sacks Endocarditis/Thrombosis:** Anti-phospholipid antibodies (APLA). * **Drug-Induced Lupus:** Anti-histone positive; Anti-dsDNA usually negative; CNS and Renal involvement are rare. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 226-230.

Q: What is the name of this chromosomal abnormality?

Ring chromosome. ***Ring chromosome*** - A **ring chromosome** forms when both **telomeric ends** of a chromosome break and fuse together, creating a **circular structure** that appears ring-shaped on karyotype. - Often associated with **loss of genetic material** at the breakpoints, leading to various developmental abnormalities and **growth retardation**. *Translocation* - Involves the **transfer of a chromosome segment** from one chromosome to another, not forming a circular structure. - Appears as **abnormal banding patterns** between two different chromosomes on karyotype, not a ring shape. *Telomeric fusion* - Refers to the **fusion of telomeres** from different chromosomes, typically resulting in **dicentric chromosomes** or chromosome bridges. - Does not create a **ring-shaped structure** but rather abnormal linear chromosome configurations. *Isochromosome* - Forms when a chromosome divides **transversely through the centromere** instead of longitudinally, creating two identical arms. - Results in a **symmetrical chromosome** with duplicated arms (e.g., i(17q)), not a circular ring structure.

Question 1

What is the total number of somatic chromosomes in a normal human diploid cell?

Accepted Answer

44

Answer

42

Answer

41

Answer

46

Question 2

What does GWAS stand for?

Accepted Answer

Genome wide Association studies

Answer

Genome wide Association syndrome

Answer

Genetic wide array studies

Answer

Genetic wide amplification studies

Question 3

A 32-year-old woman develops an Addisonian crisis (acute adrenal insufficiency) 3 months after suffering massive hemorrhage during the delivery of her baby. A CT scan of the abdomen shows small adrenal glands. Which of the following mechanisms of disease best accounts for adrenal atrophy in this patient?

Accepted Answer

Lack of trophic signals

Answer

Chronic inflammation

Answer

Chronic ischemia

Answer

Hemorrhagic necrosis

Question 4

Which stain is used to highlight the ocular basement membrane?

Accepted Answer

PAS (Periodic acid–Schiff)

Answer

Alcian blue

Answer

Methylene blue

Answer

Geimsa stain

Question 5

Karyotyping can be used to diagnose which of the following diseases?

Accepted Answer

Klinefelter’s syndrome

Answer

Multiple myeloma

Answer

Niemann-Pick disease

Answer

Pemphigus

Question 6

Which antinuclear antibody is specific for Systemic Lupus Erythematosus (SLE)?

Accepted Answer

Anti ds DNA

Answer

Anti nuclear antibodies

Answer

Anti centromere antibody

Answer

Anti histone antibody

Question 7

Which of the following statements is true regarding ataxia telangiectasia?

Accepted Answer

Increase in Alpha-fetoprotein (AFP)

Answer

Increases the risk of squamous cell carcinoma

Answer

Inherited in an autosomal dominant pattern

Answer

None of the above

Question 8

22q11 deletion leading to Di George syndrome is associated with which of the following?

Accepted Answer

Hypocalcemia

Answer

Hypokalemia

Answer

Hyperkalemia

Answer

Hypercalcemia

Question 9

What is the name of this chromosomal abnormality?

Accepted Answer

Ring chromosome

Answer

Translocation

Answer

Telomeric fusion

Answer

Isochromosome

Question 10

A one-year-old boy presented with hepatosplenomegaly and delayed milestones. Liver biopsy and bone marrow biopsy revealed the presence of histiocytes with PAS-positive diastase-resistant material in the cytoplasm. Electron-microscopic examination of these histiocytes is most likely to reveal the presence of?

Accepted Answer

Parallel arrays of tubular structures in lysosomes

Answer

Birbeck granules in the cytoplasm

Answer

Myelin figures in the cytoplasm

Answer

Electron-dense deposits in the mitochondria

Molecular Pathology — MCQs

Molecular Pathology — MCQs

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