Molecular Pathology Practice Questions

Q: Which of the following is TRUE about Turner's syndrome?

Normal intelligence. **Explanation:** Turner’s syndrome (45,X) is the most common sex chromosome abnormality in females. The correct answer is **Normal intelligence**, as most individuals with Turner’s syndrome have a normal IQ, although they may occasionally face specific neurocognitive challenges, such as difficulties with visuospatial processing or non-verbal memory. **Analysis of Options:** * **A & B (Short stature and Streak gonads):** These are the **most consistent clinical features** of Turner’s syndrome. Short stature is caused by the haploinsufficiency of the *SHOX* gene. Streak gonads (gonadal dysgenesis) occur because oocytes undergo accelerated atresia, leading to primary amenorrhea and infertility. Since these are classic pathological findings, they are "true" features, but in the context of multiple-choice questions, "Normal intelligence" is often highlighted to differentiate it from autosomal trisomies (like Down syndrome) where intellectual disability is the rule. * **D (Normal breast development):** This is **incorrect**. Due to streak gonads, there is a deficiency of estrogen. This leads to a failure of secondary sexual characteristics, resulting in poor breast development (Tanner Stage I/II) and a "shield chest" with widely spaced nipples. **High-Yield Clinical Pearls for NEET-PG:** * **Karyotype:** 45,XO is most common (50%), but mosaicism (45,X/46,XX) and structural abnormalities (isochromosome Xq) also occur. * **Cardiovascular:** Bicuspid aortic valve (most common) and Coarctation of the aorta. * **Renal:** Horseshoe kidney. * **Physical Signs:** Webbed neck (cystic hygroma remnant), lymphedema of hands/feet at birth, and cubitus valgus. * **Hormonal Profile:** Hypergonadotropic hypogonadism (High FSH/LH, Low Estrogen).

Q: All of the following statements about non-disjunction are true EXCEPT?

It cannot cause mosaicism.. **Explanation:** **Non-disjunction** is the failure of homologous chromosomes or sister chromatids to separate properly during cell division. **Why Option D is the correct answer (The Exception):** Non-disjunction **can** cause mosaicism. If non-disjunction occurs during **mitosis** in an early embryonic stage (post-zygotic), it leads to two or more cell lines with different genetic constitutions within the same individual. For example, some cells may have 46 chromosomes while others have 47 (e.g., Mosaic Down Syndrome). Therefore, the statement that it "cannot" cause mosaicism is false. **Analysis of other options:** * **Option A:** True. Non-disjunction leads to **aneuploidy** (an abnormal number of chromosomes), resulting in conditions like trisomy (2n+1) or monosomy (2n-1). * **Option B:** True. This is the fundamental definition of non-disjunction. It occurs when the spindle fibers fail to pull chromosomes to opposite poles. * **Option C:** True. It can occur in **Meiosis I** (failure of homologous chromosomes to separate), **Meiosis II** (failure of sister chromatids to separate), or **Mitosis**. **Clinical Pearls for NEET-PG:** 1. **Meiosis I non-disjunction** is the most common cause of Trisomy 21 (Down Syndrome), often associated with advanced maternal age. 2. **Mitotic non-disjunction** is the primary mechanism behind **Mosaicism**. 3. **Turner Syndrome (45, XO)** is the only viable monosomy in humans. 4. **Kleinfelter Syndrome (47, XXY)** is a classic example of sex chromosome aneuploidy caused by non-disjunction.

Q: What is the term for a single gene defect that causes multiple, seemingly unrelated problems?

Pleiotropism. **Explanation:** **1. Why Pleiotropism is Correct:** **Pleiotropism** occurs when a single gene mutation results in multiple, diverse phenotypic effects across different organ systems [1]. These effects often seem unrelated but share a common underlying biochemical or structural defect. * **Classic Example:** **Marfan Syndrome**. A mutation in the *FBN1* gene (encoding Fibrillin-1) leads to defects in the skeletal system (arachnodactyly), the ocular system (ectopia lentis), and the cardiovascular system (aortic aneurysm). **2. Why Other Options are Incorrect:** * **Pseudodominance:** This occurs when a recessive trait mimics a dominant pattern of inheritance. This happens when a person homozygous for a recessive trait mates with a heterozygote carrier, resulting in a 50% chance of affected offspring in every generation. * **Penetrance:** This refers to the percentage of individuals with a specific genotype who actually express the associated phenotype. If 100 people have the gene but only 80 show symptoms, it is "incomplete penetrance." * **Anticipation:** This is the phenomenon where a genetic disorder becomes more severe or has an earlier age of onset in successive generations. It is typically seen in **Trinucleotide Repeat Disorders** (e.g., Huntington’s disease, Fragile X syndrome). **3. Clinical Pearls for NEET-PG:** * **Variable Expressivity:** Unlike penetrance (all-or-none), this refers to the *degree* or severity of the phenotype among individuals with the same genotype. * **Locus Heterogeneity:** Mutations at different loci (different genes) produce the same phenotype (e.g., Albinism, Osteogenesis Imperfecta). * **Allelic Heterogeneity:** Different mutations within the *same* gene produce the same phenotype (e.g., Cystic Fibrosis, Beta-thalassemia). * **High-Yield Pleiotropy Example:** **Phenylketonuria (PKU)** causes mental retardation, reduced hair pigmentation, and a "mousy" odor.

Q: Study the following pedigree. What is the inheritance pattern of the disease in the family?

X-linked recessive type. ***X-linked recessive type*** - **Affected males** appear across multiple generations connected through **unaffected carrier females**, which is characteristic of X-linked recessive inheritance. - There is **no male-to-male transmission** since fathers cannot pass their X chromosome to sons, and **daughters of affected males** are obligate carriers. *Autosomal recessive type* - Would require **both parents to be carriers** for affected offspring, typically showing affected individuals in a single generation (horizontal pattern). - **Consanguinity** is often present, and both **males and females** are equally affected, which doesn't match the pedigree pattern. *Autosomal dominant type* - Would show **vertical transmission** with affected individuals in every generation having at least one affected parent. - **Male-to-male transmission** would be possible, and approximately **50% of offspring** from affected parents would be affected. *X-Linked dominant type* - **All daughters** of affected males would be affected since they must inherit the father's X chromosome. - Affected females would have **more severely affected offspring** than the pattern typically shows, and there would be more affected females overall.

Q: Which of the following chromosomal abnormalities is NOT typically associated with Down Syndrome?

Translocation (11;14). ### Explanation Down Syndrome (Trisomy 21) is the most common chromosomal disorder causing intellectual disability. It results from an extra copy of genetic material on **Chromosome 21**. **Why Option C is Correct:** **Translocation (11;14)** involves chromosomes 11 and 14. This specific translocation is classically associated with **Mantle Cell Lymphoma**, not Down Syndrome. Since it does not involve chromosome 21, it cannot result in the phenotypic expression of Down Syndrome. **Analysis of Incorrect Options:** * **Option B (Trisomy 21):** This is the most common cause (95% of cases), usually due to **maternal meiotic non-disjunction**. * **Options A & D (Robertsonian Translocations):** Approximately 3–4% of Down Syndrome cases are due to translocations. In these cases, the long arm of chromosome 21 attaches to another acrocentric chromosome. The most common partner is **chromosome 14** [t(14;21)], followed by **chromosome 15** [t(15;21)] and chromosome 22. Unlike non-disjunction, translocation-related Down Syndrome can be inherited from a carrier parent, leading to a high recurrence risk in future pregnancies. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause:** Meiotic non-disjunction (correlated with advanced maternal age). * **Recurrence Risk:** If a parent is a carrier of a **21;21 translocation**, the risk of Down Syndrome in the offspring is **100%**. * **Screening:** Low AFP, low unconjugated estriol (uE3), and high hCG/Inhibin-A are seen in the second-trimester quadruple screen. * **Cardiac:** Endocardial cushion defects (ASD/VSD) are the most common congenital heart diseases. * **GI:** Duodenal atresia ("Double bubble" sign) and Hirschsprung disease.

Question 1

Which of the following is TRUE about Turner's syndrome?

Accepted Answer

Normal intelligence

Answer

Short stature

Answer

Streak gonads

Answer

Normal breast development

Question 2

All of the following statements about non-disjunction are true EXCEPT?

Accepted Answer

It cannot cause mosaicism.

Answer

It may result in aneuploidy.

Answer

It is the failure of chromosomes to separate normally during cell division.

Answer

It may occur in meiosis or mitosis.

Question 3

What is the term for a single gene defect that causes multiple, seemingly unrelated problems?

Accepted Answer

Pleiotropism

Answer

Pseudodominance

Answer

Penetrance

Answer

Anticipation

Question 4

Which method is used to detect the BCR-ABL fusion gene?

Accepted Answer

FISH

Answer

Flow cytometry

Answer

Karyotyping

Answer

RT-PCR

Question 5

Which of the following is NOT an advantage of nanotechnology in cancer diagnosis?

Accepted Answer

Nanocrystals exhibit a narrow difference between their excitation and emission peak spectra.

Answer

Nanocrystals exhibit bright, photostable fluorescence.

Answer

Nanocrystals have a narrow spectrum wavelength.

Answer

Peak spectrum wavelength is tunable.

Question 6

A 38-year-old woman shows evidence of early cataracts, hair loss, atrophy of skin, osteoporosis, and accelerated atherosclerosis. This patient has most likely inherited mutations in both alleles of a gene that encodes which of the following types of intracellular proteins?

Accepted Answer

Helicase

Answer

Deaminase

Answer

Oxidase

Answer

Polymerase

Question 7

Study the following pedigree. What is the inheritance pattern of the disease in the family?

Accepted Answer

X-linked recessive type

Answer

Autosomal recessive type

Answer

Autosomal dominant type

Answer

X-Linked dominant type

Question 8

Turner syndrome is characterized by which chromosomal abnormality?

Accepted Answer

45, XO

Answer

47, XXY

Answer

Trisomy 13

Answer

Trisomy 18

Question 9

Translocation between two acrocentric chromosomes occurs with breakpoints near the centromeres, resulting in very large and very small chromosomes. The smaller fragment is typically lost. What is this type of cytogenetic abnormality?

Accepted Answer

Robertsonian translocation

Answer

Deletion

Answer

Balanced translocation

Answer

Inversion

Question 10

Which of the following chromosomal abnormalities is NOT typically associated with Down Syndrome?

Accepted Answer

Translocation (11;14)

Answer

Translocation (14;21)

Answer

Trisomy 21

Answer

Translocation (15;21)

Molecular Pathology — MCQs

Molecular Pathology — MCQs

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