Cytogenetics — MCQs
What is the name of the syndrome associated with the deletion of chromosome 22?
Karyotyping is done in which phase of the cell cycle?
Which of the following is not the karyotype of Turner syndrome?
Which investigation is the gold standard for diagnosing Edwards syndrome?
Number of chromosomes in Klinefelter syndrome:
A patient of 47XXY karyotype with features of hypogonadism; likely diagnosis is :
Which of the following is a characteristic feature of Down syndrome?
Molecular genetic testing is used to detect all of the following except?
What is the most common type of acute myeloid leukemia in patients with Down's syndrome?
Barr bodies are seen in which of the following conditions?
Cytogenetics Indian Medical PG Practice Questions and MCQs
Question 1: What is the name of the syndrome associated with the deletion of chromosome 22?
- A. Down syndrome
- B. Di George syndrome (Correct Answer)
- C. Turner syndrome
- D. Klinefelter syndrome
- E. Prader-Willi syndrome
Explanation: ***Di George syndrome*** - Di George syndrome, also known as **22q11.2 deletion syndrome**, is caused by a deletion on the long arm of chromosome 22. - This syndrome is associated with varied clinical features, including **congenital heart defects**, **thymic hypoplasia** (leading to immune deficiencies), **hypocalcemia** due to parathyroid hypoplasia, and characteristic facial features. *Down syndrome* - Down syndrome is caused by a **trisomy of chromosome 21**, meaning there's an extra copy of chromosome 21. - It is characterized by intellectual disability, distinctive facial features, and developmental delays, and is not associated with chromosome 22 deletion. *Turner syndrome* - Turner syndrome is a chromosomal condition affecting females, characterized by the partial or complete absence of one of the **X chromosomes (45, X0)**. - It leads to short stature, ovarian dysfunction, and characteristic physical features, unrelated to chromosome 22. *Klinefelter syndrome* - Klinefelter syndrome is a chromosomal disorder in males resulting from an extra **X chromosome (47, XXY)**. - Individuals often experience hypogonadism, reduced fertility, and abnormal body proportions, which is distinct from a deletion on chromosome 22. *Prader-Willi syndrome* - Prader-Willi syndrome is caused by a **deletion of paternal chromosome 15q11-q13** or maternal uniparental disomy. - It presents with hypotonia, hyperphagia, obesity, intellectual disability, and hypogonadism, unrelated to chromosome 22 deletion.
Question 2: Karyotyping is done in which phase of the cell cycle?
- A. Anaphase
- B. Metaphase (Correct Answer)
- C. Telophase
- D. S phase
Explanation: ***Metaphase*** - During **metaphase**, chromosomes are maximally condensed and aligned at the **metaphase plate**, making them most visible and easy to distinguish under a microscope. - This condensation and alignment are crucial for accurate visualization and analysis of chromosome number and structure in **karyotyping**. *Anaphase* - In **anaphase**, sister chromatids separate and move to opposite poles, which makes them difficult to organize and analyze systematically for karyotyping. - The chromosomes are in motion and becoming less condensed as they move apart, which is not ideal for imaging. *Telophase* - During **telophase**, chromosomes decondense and nuclear envelopes reform, making them invisible or poorly defined for microscopic analysis. - The cell is also preparing to divide, and the chromosomes are no longer individually distinct structures suitable for karyotyping. *S phase* - The **S (synthesis) phase** is when DNA replication occurs, and chromosomes are replicated but remain in a decondensed state as chromatin. - In this phase, individual chromosomes are not condensed or visible as distinct structures, making them unsuitable for karyotyping.
Question 3: Which of the following is not the karyotype of Turner syndrome?
- A. 45 XO
- B. 46,X,r(X)
- C. 46,X,i(Xp) (Correct Answer)
- D. 46,X, i(X) (q10)
Explanation: ***46,X,i(Xp)*** - This karyotype indicates an **isochromosome of the short arm of the X chromosome**, with two copies of Xp and complete loss of Xq. - This results in **duplication of Xp material** (including the critical SHOX gene region), which **prevents the characteristic short stature** of Turner syndrome [1]. - While Xq material is lost, the **presence of two Xp arms protects against the Turner phenotype**, making this karyotype **NOT typically associated with Turner syndrome**. Just as the loss of SHOX is associated with short stature, excess copies are associated with tall stature [1]. - This is an extremely rare karyotype that does not produce the classic Turner syndrome features. *45,XO* - This is the **classic and most common karyotype for Turner syndrome** (about 50-60% of cases), characterized by complete absence of one X chromosome. - Results in characteristic features: **short stature, gonadal dysgenesis, webbed neck, cardiac anomalies**, and lymphedema. *46,X,r(X)* - This karyotype has a **ring X chromosome**, where both ends of the X chromosome have fused together, typically with loss of genetic material from both arms. - The loss of critical genes leads to **Turner syndrome phenotype** due to haploinsufficiency. - Ring X chromosomes account for approximately 5% of Turner syndrome cases. *46,X,i(X)(q10)* - This is an **isochromosome of the long arm of the X chromosome** (i(Xq)), with two copies of Xq and complete loss of Xp [1]. - The **loss of Xp material (including SHOX gene)** causes the characteristic **short stature and skeletal abnormalities** of Turner syndrome [1]. - This is the **second most common structural abnormality** causing Turner syndrome (15-20% of cases). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 169-177.
Question 4: Which investigation is the gold standard for diagnosing Edwards syndrome?
- A. Karyotype (Correct Answer)
- B. MLPA
- C. Microarray
- D. FISH
Explanation: ***Karyotype*** - A **karyotype** is considered the **gold standard** for diagnosing chromosomal abnormalities like **Edwards syndrome** (Trisomy 18) because it allows for the visualization and analysis of all 46 chromosomes [1]. - It can detect changes in chromosome number (aneuploidy) and large structural rearrangements, directly confirming the presence of an extra chromosome 18 [2]. *MLPA (Multiplex Ligation-dependent Probe Amplification)* - **MLPA** is a molecular technique used to detect **copy number variations** for specific targeted regions but does not provide a comprehensive view of the entire karyotype. - While it can detect trisomies, it is generally used for specific gene deletions or duplications and is not the first-line diagnostic method for whole chromosome aneuploidies like Edwards syndrome. *Microarray (Chromosomal Microarray Analysis)* - **Microarray** is a high-resolution method that can detect smaller deletions and duplications (microdeletions/microduplications) unidentifiable by traditional karyotyping. - However, for whole chromosome trisomies, a **karyotype** remains the gold standard as it directly visualizes the extra chromosome rather than inferring its presence through copy number changes of multiple probes [3]. *FISH (Fluorescence In Situ Hybridization)* - **FISH** is a targeted technique that uses fluorescent probes to detect specific chromosomal regions or whole chromosomes [3]. - While useful for rapid detection of common aneuploidies or specific translocations, it requires prior suspicion of a particular chromosomal abnormality and does not provide a comprehensive global view of all chromosomes like a traditional **karyotype** [3]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 167-168. [2] 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. 54-55. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 186-187.
Question 5: Number of chromosomes in Klinefelter syndrome:
- A. 44
- B. 46
- C. 47 (Correct Answer)
- D. 45
Explanation: ***47*** - **Klinefelter syndrome** is a genetic condition in males characterized by the presence of an extra X chromosome, resulting in a **47, XXY karyotype** [1]. - This additional chromosome increases the total count from the typical 46 to **47** [1]. *44* - A count of 44 chromosomes would indicate either a severe **aneuploidy** or a **haploid** state, which is not compatible with human life in a full somatic cell. - Normal human somatic cells contain 46 chromosomes (2n). *46* - A count of 46 chromosomes represents the **normal diploid number** for human somatic cells (46, XX for females and 46, XY for males). - This count would signify a genetically typical individual, not someone with Klinefelter syndrome. *45* - A count of 45 chromosomes typically indicates a **monosomy**, such as **Turner syndrome** (45, X) in females, where one sex chromosome is missing. - This is a different chromosomal abnormality from Klinefelter syndrome, which involves an extra chromosome. **References:** [1] 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. 92-93.
Question 6: A patient of 47XXY karyotype with features of hypogonadism; likely diagnosis is :
- A. Turners syndrome
- B. Down syndrome
- C. Klinefelter's syndrome (Correct Answer)
- D. Edwards syndrome
Explanation: ***Klinefelter's syndrome*** - **Klinefelter's syndrome** is characterized by a **47,XXY karyotype**, which is a genetic condition affecting males [1]. - Individuals with this syndrome often present with **hypogonadism**, leading to features such as small testes, infertility, and reduced secondary sexual characteristics [2]. *Turners syndrome* - **Turner's syndrome** is a genetic condition affecting females, characterized by a **45,X karyotype**, meaning they are missing all or part of one X chromosome [2]. - While it also involves hypogonadism, it does not present with an **XXY karyotype** or affect males [3]. *Down syndrome* - **Down syndrome**, or trisomy 21, is caused by an extra copy of chromosome 21, resulting in a **47,XX,+21 or 47,XY,+21 karyotype**. - It is characterized by intellectual disability, distinctive facial features, and developmental delays, not typically hypogonadism associated with an XXY karyotype. *Edwards syndrome* - **Edwards syndrome**, or trisomy 18, is caused by an extra copy of chromosome 18, resulting in a **47,XX,+18 or 47,XY,+18 karyotype**. - This syndrome is associated with severe developmental abnormalities, intellectual disability, and a very short lifespan, with different clinical features from the given description.
Question 7: Which of the following is a characteristic feature of Down syndrome?
- A. Trisomy 18
- B. Robertsonian translocation involving chromosome 21
- C. Trisomy 21 (Correct Answer)
- D. Trisomy 13
Explanation: ***Trisomy 21*** - **Down syndrome** is the most common autosomal chromosome abnormality and is characterized by the presence of an extra copy of chromosome 21 [1, 2]. - This extra genetic material leads to the characteristic physical features, intellectual disability, and medical conditions associated with the syndrome [1, 2]. *Trisomy 18* - **Trisomy 18**, also known as **Edwards syndrome**, is a serious chromosomal disorder distinct from Down syndrome [2]. - It is characterized by severe developmental problems, including **heart defects**, **kidney malformations**, and **severe intellectual disability**, with generally a much shorter life expectancy [2, 3]. *Robertsonian translocation involving chromosome 21* - A **Robertsonian translocation** involving chromosome 21 is a cause of Down syndrome, but it is not the characteristic feature itself; rather, it is a specific **chromosomal rearrangement** that can lead to an extra copy of chromosome 21 material [1, 2]. - This specific type of translocation accounts for only a small percentage (2-3%) of all Down syndrome cases, while **Trisomy 21** (nondisjunction) is the most common cause [1, 2]. *Trisomy 13* - **Trisomy 13**, also known as **Patau syndrome**, is a distinct chromosomal disorder characterized by the presence of an extra copy of chromosome 13 [2]. - It is associated with severe birth defects, including **cleft lip/palate**, **polydactyly**, and severe neurological problems, and is usually fatal within the first year of life [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 170-171. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 171-172. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 168-169.
Question 8: Molecular genetic testing is used to detect all of the following except?
- A. Translocation (Correct Answer)
- B. Point mutation
- C. Amplification
- D. Deletion
Explanation: ***Translocation*** - This is the **intended answer** for this question, based on a distinction between traditional molecular genetic testing and cytogenetic methods. - Historically, **large-scale chromosomal translocations** were primarily identified by **conventional cytogenetic methods** like **karyotyping**. - However, in modern practice, translocations **can be detected** by molecular techniques including **FISH (fluorescence in situ hybridization)**, **RT-PCR** for specific fusion genes (e.g., BCR-ABL), and **next-generation sequencing** [3], [4]. - The distinction is becoming less clear as molecular cytogenetic techniques bridge both fields. *Point mutation* - **Single nucleotide changes** (point mutations) are the **classic target** of molecular genetic testing [1]. - Readily detected by **Sanger sequencing**, **next-generation sequencing**, **PCR-based methods**, and **allele-specific assays** [3]. - These tests specifically identify alterations in individual DNA bases. *Amplification* - **Gene amplifications** (increased copy number) are routinely detected using molecular genetic techniques. - Methods include **quantitative PCR (qPCR)**, **digital PCR**, **FISH**, and **array comparative genomic hybridization (aCGH)** [2]. - Example: HER2 amplification testing in breast cancer. *Deletion* - **Deletions** ranging from single nucleotides to whole genes are readily detectable by molecular genetic testing [1]. - Techniques include **multiplex ligation-dependent probe amplification (MLPA)**, **aCGH**, **next-generation sequencing**, and **deletion-specific PCR** [2], [3]. - Small and large deletions are both within the scope of modern molecular diagnostics [1], [3]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 183-184. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 186-187. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 185-186. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 342-343.
Question 9: What is the most common type of acute myeloid leukemia in patients with Down's syndrome?
- A. Acute megakaryoblastic leukemia M7 (Correct Answer)
- B. Acute myeloid leukemia M1
- C. Acute promyelocytic leukemia M3
- D. Acute myeloid leukemia M2
Explanation: ***Acute megakaryoblastic leukemia M7*** - **Acute megakaryoblastic leukemia (AML M7)** is significantly more common in children with **Down's syndrome (trisomy 21)**, particularly those under 5 years of age. - This association is thought to be due to an increased copy number of certain genes on **chromosome 21** that are involved in hematopoiesis and leukemogenesis. [3] *Acute myeloid leukemia M1* - This subtype, characterized by proliferation of **myeloblasts without maturation**, is not specifically associated with Down's syndrome. [1] - It is a more undifferentiated form of AML. *Acute promyelocytic leukemia M3* - Characterized by the t(15;17) translocation involving the **PML-RARα fusion gene**, resulting in a block in myeloid differentiation at the promyelocyte stage. [2], [4], [5] - This subtype is associated with a specific genetic abnormality and is not preferentially seen in patients with Down's syndrome. *Acute myeloid leukemia M2* - This subtype involves **myeloblasts with maturation** and a characteristic t(8;21) chromosomal translocation. [2] - While it's a common form of AML, it does not show the specific strong association with Down's syndrome that AML M7 does. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 607-608. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, p. 620. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 170-171. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, pp. 621-622. [5] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, pp. 620-621.
Question 10: Barr bodies are seen in which of the following conditions?
- A. 46 XY
- B. Klinefelter's syndrome (Correct Answer)
- C. Testicular feminization syndrome
- D. Turner's syndrome
Explanation: ***Klinefelter's syndrome*** - Individuals with **Klinefelter's syndrome** have a **47, XXY karyotype**, meaning they have two X chromosomes. - One of these X chromosomes undergoes **X-inactivation** to form a Barr body, which is a condensed, inactive X chromosome [1]. *Turners syndrome* - Individuals with **Turner's syndrome** typically have a **45, XO karyotype**, meaning they have only one X chromosome [1]. - Since they lack a second X chromosome, they do not form a **Barr body**. *Testicular feminization syndrome* - Individuals with **testicular feminization syndrome** (now known as **Androgen Insensitivity Syndrome**) have a **46, XY karyotype**. - As they have only one X chromosome, they do not form a **Barr body**. *46 XY* - A **46, XY karyotype** represents a typical male, meaning they have one X and one Y chromosome. - Since they have only one X chromosome, they do not form a **Barr body**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 173-174.
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