Chromosomal abnormalities and syndromes MCQs With Answer

Introduction

Chromosomal abnormalities and syndromes MCQs With Answer is designed for M.Pharm students specializing in Advanced Pharmaceutical Biotechnology. This collection focuses on the genetic basis, cytogenetic mechanisms, diagnostic techniques, and clinical correlations of numerical and structural chromosomal disorders. Questions range from principles of nondisjunction, mosaicism, and imprinting to applied knowledge about Down, Turner, Klinefelter, DiGeorge, Cri-du-chat, and Fragile X syndromes. Diagnostic methods such as karyotyping, FISH, array-CGH and noninvasive prenatal testing are emphasized with clinical implications and recurrence risk considerations. The quiz aims to deepen conceptual understanding and prepare students for research, clinical interpretation, and therapeutics related to chromosomal pathologies.

Q1. What is the most common cytogenetic mechanism producing trisomy 21 (Down syndrome) in liveborn infants?

• An unbalanced Robertsonian translocation inherited from a parent
• Maternal meiotic nondisjunction resulting in an extra chromosome 21
• Paternal meiotic recombination errors
• Postzygotic mitotic error producing mosaicism

Correct Answer: Maternal meiotic nondisjunction resulting in an extra chromosome 21

Q2. Which cytogenetic technique has the highest resolution for detecting submicroscopic copy number variants across the genome?

• Conventional G-banded karyotype
• Fluorescence in situ hybridization (FISH) with locus-specific probes
• Array comparative genomic hybridization (array-CGH / chromosomal microarray)
• Electron microscopy

Correct Answer: Array comparative genomic hybridization (array-CGH / chromosomal microarray)

Q3. Which statement best describes a Robertsonian translocation?

• An inversion within the short arm of an acrocentric chromosome
• A centric fusion between two acrocentric chromosomes resulting in a single large chromosome
• A duplication of the long arm of a metacentric chromosome
• The formation of a ring chromosome from terminal deletions

Correct Answer: A centric fusion between two acrocentric chromosomes resulting in a single large chromosome

Q4. Which chromosomal syndrome is classically associated with short stature, streak gonads, and horseshoe kidney?

• Klinefelter syndrome (47,XXY)
• Turner syndrome (45,X)
• Prader-Willi syndrome (15q11-q13 deletion)
• Williams syndrome (7q11.23 deletion)

Correct Answer: Turner syndrome (45,X)

Q5. Which technique is most appropriate to detect a balanced translocation in a parent of a child with an unbalanced karyotype?

• High-resolution oligonucleotide array-CGH
• Metaphase G-banded karyotype analysis
• Quantitative PCR for copy number
• Southern blot for repeat expansions

Correct Answer: Metaphase G-banded karyotype analysis

Q6. Fragile X syndrome is caused by which of the following molecular lesions?

• Deletion of the FMR1 gene on chromosome 15
• CGG trinucleotide repeat expansion in the 5′ UTR of FMR1 on X chromosome
• Missense mutation in MECP2 gene
• Triplication of the MECP2 locus

Correct Answer: CGG trinucleotide repeat expansion in the 5′ UTR of FMR1 on X chromosome

Q7. Which syndrome is most commonly due to a microdeletion at 22q11.2 and presents with cardiac defects, cleft palate, and immune deficiency?

• Williams syndrome
• DiGeorge (22q11.2 deletion) syndrome
• Angelman syndrome
• Cri-du-chat syndrome

Correct Answer: DiGeorge (22q11.2 deletion) syndrome

Q8. Which prenatal screening method analyzes cell-free fetal DNA in maternal plasma to estimate risk of common trisomies?

• Chorionic villus sampling (CVS)
• Amniocentesis with fetal karyotype
• Noninvasive prenatal testing (NIPT) using cell-free DNA
• Ultrasound nuchal translucency alone

Correct Answer: Noninvasive prenatal testing (NIPT) using cell-free DNA

Q9. Uniparental disomy (UPD) can cause disease through which primary mechanism?

• Dosage increase because both copies are duplicated
• Loss of heterozygosity leading to expression of recessive mutations only when both parents contributed the same allele
• Aberrant imprinting causing loss or duplication of parent-of-origin-specific gene expression
• Formation of ring chromosomes

Correct Answer: Aberrant imprinting causing loss or duplication of parent-of-origin-specific gene expression

Q10. Which chromosomal abnormality is characterized by a high-pitched “cat-like” cry in infancy due to a deletion on the short arm of chromosome 5?

• Cri-du-chat syndrome (5p-)
• Wolf-Hirschhorn syndrome (4p-)
• Smith-Magenis syndrome (17p11.2 deletion)
• Beckwith-Wiedemann syndrome (11p15 imprinting disturbance)

Correct Answer: Cri-du-chat syndrome (5p-)

Q11. Which of the following is a limitation of array-CGH compared with conventional karyotype?

• Array-CGH cannot detect small copy number variants below 1 kb
• Array-CGH cannot detect balanced rearrangements such as reciprocal translocations
• Array-CGH has lower sensitivity for submicroscopic deletions than FISH
• Array-CGH cannot detect aneuploidies

Correct Answer: Array-CGH cannot detect balanced rearrangements such as reciprocal translocations

Q12. Mosaic Turner syndrome differs from classic Turner syndrome primarily by which feature?

• Mosaic Turner results from paternal nondisjunction only
• Mosaic Turner shows the presence of two or more cell lines with different karyotypes, often with milder phenotype
• Mosaic Turner always results in spontaneous puberty and fertility
• Mosaic Turner is characterized by an extra X chromosome in all cells

Correct Answer: Mosaic Turner shows the presence of two or more cell lines with different karyotypes, often with milder phenotype

Q13. Which phenotypic features best distinguish Edwards syndrome (trisomy 18) from Patau syndrome (trisomy 13)?

• Polydactyly and holoprosencephaly are more typical of trisomy 18
• Omphalocele and neural tube defects are exclusive to trisomy 18
• Microphthalmia, polydactyly, and cleft lip/palate are more characteristic of trisomy 13
• Single palmar crease is diagnostic of trisomy 13

Correct Answer: Microphthalmia, polydactyly, and cleft lip/palate are more characteristic of trisomy 13

Q14. Which structural chromosome abnormality results when breaks in a chromosome produce loss of both terminal segments and fusion of the ends into a circular structure?

• Isochromosome formation
• Ring chromosome formation
• Pericentric inversion
• Robertsonian translocation

Correct Answer: Ring chromosome formation

Q15. A mother carries a balanced Robertsonian translocation between chromosomes 14 and 21 but is phenotypically normal. What risk is most relevant to genetic counseling for Down syndrome in future offspring?

• No increased risk because parents are phenotypically normal
• Increased risk of having a child with unbalanced segregation resulting in trisomy 21
• 100% risk of having a child with Turner syndrome
• Increased risk only for sex chromosome aneuploidy

Correct Answer: Increased risk of having a child with unbalanced segregation resulting in trisomy 21

Q16. Which clinical scenario is most suggestive of genomic imprinting as the disease mechanism?

• A disease manifesting equally whether the mutated allele is inherited from mother or father
• A disease where clinical outcome depends on whether a deletion is inherited from the mother or father (e.g., Prader-Willi vs Angelman)
• A disease caused exclusively by de novo point mutations in a mitochondrial gene
• A disease caused by somatic mosaicism limited to skin

Correct Answer: A disease where clinical outcome depends on whether a deletion is inherited from the mother or father (e.g., Prader-Willi vs Angelman)

Q17. Which laboratory method is most useful to confirm a suspected microdeletion syndrome when a specific small region is targeted and rapid results are needed?

• Whole-genome sequencing
• Targeted FISH using locus-specific probes
• High-resolution G-banded karyotype
• Sanger sequencing of candidate genes

Correct Answer: Targeted FISH using locus-specific probes

Q18. Which statement best explains why advanced maternal age increases risk of aneuploidy in offspring?

• Older oocytes have increased meiotic nondisjunction due to aging-related defects in meiotic spindle and cohesion proteins
• Sperm quality becomes the main determinant of aneuploidy with maternal age
• Advanced maternal age exclusively causes structural chromosome rearrangements
• Maternal age increases likelihood of paternal translocations

Correct Answer: Older oocytes have increased meiotic nondisjunction due to aging-related defects in meiotic spindle and cohesion proteins

Q19. Which description accurately defines mosaicism?

• Presence of a deletion in all somatic and germline cells
• Presence of two or more genetically distinct cell lines derived from a single zygote
• Inheritance of two identical chromosomes from one parent
• Transient chromosomal instability in cancer cells only

Correct Answer: Presence of two or more genetically distinct cell lines derived from a single zygote

Q20. Which of the following syndromes results from a contiguous gene deletion on chromosome 7q11.23 and is associated with unique cardiovascular findings and an overly friendly personality?

• Williams syndrome
• DiGeorge syndrome
• Angelman syndrome
• Beckwith-Wiedemann syndrome

Correct Answer: Williams syndrome

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