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Question 1. Which nitrogenous base pairs with adenine in DNA? A) Guanine B) Cytosine C) Thymine D) Uracil Answer: C Explanation: Adenine forms two hydrogen bonds with thymine in double‑stranded DNA. Question 2. The sugar component of a DNA nucleotide is: A) Ribose B) Deoxyribose C) Glucose D) Fructose Answer: B Explanation: DNA contains deoxyribose, lacking an OH group at the 2’ carbon. Question 3. Which statement best describes the antiparallel orientation of DNA strands? A) Both run 5’→3’ B) Both run 3’→5’ C) One runs 5’→3’, the other 3’→5’ D) Strands are parallel but offset Answer: C Explanation: DNA strands run in opposite directions, enabling complementary base pairing. Question 4. In the human genome, approximately how many protein‑coding genes are present? A) 5,000 B) 20,000 C) 50,000 D) 100, Answer: B Explanation: Current estimates place the number of protein‑coding genes near 20 k. Question 5. Which enzyme synthesizes mRNA during transcription? A) DNA polymerase B) RNA polymerase C) Reverse transcriptase D) Ligase Answer: B Explanation: RNA polymerase reads the DNA template and builds a complementary RNA strand. Question 6. The start codon for translation in eukaryotes is: A) UGA B) UAA C) AUG D) UAG Answer: C
Explanation: AUG codes for methionine and signals the ribosome to begin translation. Question 7. Which of the following processes occurs in the cytoplasm? A) Transcription B) DNA replication C) Translation D) RNA splicing Answer: C Explanation: Ribosomes translate mRNA into protein in the cytoplasm. Question 8. A frameshift mutation is most likely caused by: A) A single base substitution B) An insertion or deletion not divisible by three C) A silent mutation D) A synonymous substitution Answer: B Explanation: Adding or removing nucleotides shifts the reading frame unless the change is in multiples of three. Question 9. Which type of mutation is most likely to have no effect on the protein sequence? A) Missense B) Nonsense C) Silent D) Frameshift Answer: C Explanation: Silent mutations change a codon to another that codes for the same amino acid. Question 10. Mitochondrial DNA is inherited: A) Paternally B) Maternal only C) Both parents equally D) Randomly from either parent Answer: B Explanation: Mitochondria are transmitted through the oocyte, so mtDNA follows maternal inheritance. Question 11. An autosomal recessive disease manifests when: A) One allele is mutant B) Both alleles are mutant C) The mutant allele is on the X chromosome D) The allele is mitochondrial Answer: B Explanation: Two copies of the recessive allele are required for phenotypic expression.
Question 17. Which of the following is a non‑coding RNA that regulates gene expression post‑transcriptionally? A) tRNA B) rRNA C) miRNA D) mRNA Answer: C Explanation: MicroRNAs bind target mRNAs to inhibit translation or promote degradation. Question 18. The “central dogma” of molecular biology states: A) DNA → RNA → Protein B) Protein → RNA → DNA C) RNA → DNA → Protein D) DNA ↔ RNA ↔ Protein Answer: A Explanation: Genetic information flows from DNA to RNA to protein. Question 19. A heterozygous individual for an X‑linked recessive trait will: A) Express the trait if male B) Express the trait if female C) Never express the trait D) Express the trait only if homozygous Answer: B Explanation: Females have two X chromosomes; a single recessive allele can be masked, but carrier females may show mild symptoms. Question 20. Which of the following best describes a polygenic risk score (PRS)? A) Sum of rare pathogenic variants B) Weighted count of many common alleles C) Single SNP effect size D) Measure of epigenetic age Answer: B Explanation: PRS aggregates the small effects of many common variants to estimate disease risk. Question 21. The effect of a missense mutation is most often: A) No change B) Altered amino acid C) Premature stop codon D) Frame shift Answer: B Explanation: Missense mutations replace one amino acid with another, potentially affecting protein function.
Question 22. Which cellular organelle contains its own DNA? A) Nucleus B) Mitochondrion C) Golgi apparatus D) Endoplasmic reticulum Answer: B Explanation: Mitochondria possess circular DNA encoding some of their own proteins. Question 23. Which process removes introns from pre‑mRNA? A) Splicing B) Capping C) Polyadenylation D) Export Answer: A Explanation: The spliceosome excises introns, joining exons to produce mature mRNA. Question 24. In the context of pharmacogenomics, a “poor metabolizer” phenotype for CYP2D typically leads to: A) Faster drug clearance B) Lower drug efficacy C) Higher plasma drug levels D) No effect on drug response Answer: C Explanation: Reduced enzyme activity slows metabolism, increasing drug concentration and risk of toxicity. Question 25. Which of the following lifestyle factors is most strongly linked to DNA methylation changes in the IGF2 gene? A) High‑protein diet B) Chronic stress C) Regular exercise D) Vitamin C supplementation Answer: B Explanation: Psychosocial stress has been shown to alter methylation patterns at imprinted loci like IGF2. Question 26. The legal act that protects U.S. workers from genetic discrimination in health insurance is: A) ADA B) HIPAA C) GINA D) ACA Answer: C
Question 32. Which phase of the cell cycle is DNA replication completed? A) G1 B) S C) G2 D) M Answer: B Explanation: The S (synthesis) phase is when the genome is duplicated. Question 33. A “gain‑of‑function” mutation typically results in: A) Loss of protein activity B) No phenotypic change C) New or increased activity D) Protein truncation Answer: C Explanation: Gain‑of‑function alleles endow proteins with novel or heightened functions. Question 34. The term “haplotype” refers to: A) A single SNP B) A set of alleles inherited together C) The entire genome D) A mutated gene copy Answer: B Explanation: A haplotype is a group of linked variants transmitted as a block. Question 35. Which of the following best describes “informed consent” for genetic testing? A) Mandatory signing of a waiver B) Provision of test results only C) Explanation of risks, benefits, and alternatives D) No discussion needed if test is low‑risk Answer: C Explanation: Clients must understand potential outcomes before agreeing to testing. Question 36. Which of the following is a common epigenetic effect of chronic alcohol consumption? A) Global DNA hypomethylation B) Increased histone acetylation C) Telomere elongation D) Increased mitochondrial DNA copy number Answer: A Explanation: Alcohol can reduce methylation across the genome, altering gene expression.
Question 37. The “double‑helix” model of DNA was first proposed by: A) Watson and Crick B) Mendel C) Franklin D) Avery Answer: A Explanation: James Watson and Francis Crick described the complementary helical structure in 1953. Question 38. Which of the following best describes a “carrier” in autosomal recessive inheritance? A) Affected individual B) Unaffected individual with one mutant allele C) Unaffected individual with two normal alleles D) Affected male only Answer: B Explanation: Carriers possess one pathogenic allele but do not show the disease phenotype. Question 39. In eukaryotes, the 5’ cap added to nascent mRNA serves to: A) Facilitate nuclear export B) Promote degradation C) Inhibit translation D) Remove introns Answer: A Explanation: The 7‑methylguanosine cap protects mRNA and aids export to the cytoplasm. Question 40. Which of the following is a direct consequence of a nonsense mutation? A) Extended protein B) Truncated protein C) No change D) Frame shift Answer: B Explanation: A premature stop codon leads to early termination of translation. Question 41. Which genetic condition is most commonly associated with a mutation in the BRCA gene? A) Cystic fibrosis B) Breast and ovarian cancer C) Hemophilia D) Sickle cell disease Answer: B Explanation: BRCA1 pathogenic variants markedly increase risk for breast and ovarian cancers.
Question 47. Which of the following best describes “linkage disequilibrium”? A) Random assortment of alleles B) Non‑random association of alleles at different loci C) Complete independence of loci D) Equal recombination rates across genome Answer: B Explanation: LD occurs when specific allele combinations are inherited together more often than expected. Question 48. Which protein complex is responsible for unwinding DNA during transcription? A) DNA ligase B) Helicase C) Topoisomerase D) Polymerase Answer: B Explanation: RNA polymerase recruits helicase activity to separate strands for template reading. Question 49. The “reading frame” of a gene is determined by: A) The promoter region B) The start codon C) The splice sites D) The poly‑A tail Answer: B Explanation: Translation initiates at the start codon, establishing the triplet codon boundaries. Question 50. Which of the following is a common method to assess DNA methylation status genome‑wide? A) Western blot B) Bisulfite sequencing C) Southern blot D) ELISA Answer: B Explanation: Bisulfite conversion differentiates methylated from unmethylated cytosines for sequencing. Question 51. Which of the following is an example of a recessive X‑linked disorder? A) Hemophilia A B) Duchenne muscular dystrophy C) Fragile X syndrome D) Turner syndrome Answer: A Explanation: Hemophilia A is caused by recessive mutations on the X chromosome.
Question 52. In the context of gene expression, the term “up‑regulation” means: A) Decreased transcription B) Increased transcription C) Gene deletion D) Gene silencing Answer: B Explanation: Up‑regulation refers to enhanced synthesis of mRNA or protein. Question 53. Which of the following best describes a “pharmacogenomic panel”? A) A list of all possible drugs B) A set of genetic markers predicting drug response C) A dosage chart for antibiotics D) A survey of patient adherence Answer: B Explanation: Panels test multiple variants (e.g., CYP genes) to guide medication choices. Question 54. The term “epistasis” refers to: A) Interaction between alleles at the same locus B) Interaction between genes at different loci C) Random mutation D) Gene duplication Answer: B Explanation: Epistasis occurs when one gene’s effect masks or modifies another’s. Question 55. Which of the following is a primary function of histone acetyltransferases (HATs)? A) Add methyl groups to DNA B) Remove acetyl groups from histones C) Add acetyl groups to histone tails D) Degrade histones Answer: C Explanation: HATs acetylate lysine residues, loosening chromatin and promoting transcription. Question 56. Which of the following is a characteristic of a “founder effect” in population genetics? A) High mutation rate B) Reduced genetic diversity due to a small initial group C) Random mating D) Large, stable population size Answer: B Explanation: When a new population originates from few individuals, allele frequencies may be skewed.
Answer: B Explanation: Telomeres consist of tandem repeats (TTAGGG) that protect chromosome ends. Question 63. Which of the following best describes the role of the “spliceosome”? A) Adds the 5’ cap B) Removes introns C) Polyadenylates mRNA D) Initiates translation Answer: B Explanation: The spliceosome catalyzes intron excision during pre‑mRNA processing. Question 64. In pharmacogenomics, a “CYP2C19*2” allele is associated with: A) Ultra‑rapid metabolism of clopidogrel B) Reduced metabolism of clopidogrel C) No effect on drug metabolism D) Increased metabolism of warfarin Answer: B Explanation: The *2 loss‑of‑function variant diminishes activation of clopidogrel. Question 65. Which of the following is a common epigenetic consequence of chronic high‑fat diet in rodents? A) Global DNA hypermethylation B) Histone deacetylation at metabolic genes C) Increased telomere length D) Mitochondrial DNA duplication Answer: B Explanation: High‑fat feeding often leads to histone deacetylation, repressing genes involved in lipid metabolism. Question 66. Which of the following best describes a “single‑nucleotide polymorphism (SNP)”? A) A DNA segment duplicated B) A single base change present in ≥1% of population C) A large chromosomal inversion D) An RNA editing event Answer: B Explanation: SNPs are common single‑base variations with a minor allele frequency of at least 1%.
Question 67. The “Hardy‑Weinberg equilibrium” assumes which of the following conditions? A) Small population size B) Non‑random mating C) No mutation, migration, selection D) Continuous selection pressure Answer: C Explanation: Equilibrium requires no external forces altering allele frequencies. Question 68. Which of the following best explains why “X‑inactivation” occurs in female mammals? A) To double gene dosage B) To silence the Y chromosome C) To equalize X‑linked gene expression between sexes D) To increase mutation rate Answer: C Explanation: Random inactivation of one X chromosome balances dosage with XY males. Question 69. In the context of health‑risk assessment, a “polygenic risk score” is calculated by: A) Counting the number of pathogenic mutations B) Summing weighted effect sizes of many SNPs C) Measuring telomere length D) Assessing DNA methylation age Answer: B Explanation: PRS aggregates small contributions from numerous common variants. Question 70. Which of the following is a hallmark of “genomic instability” in cancer cells? A) High fidelity DNA repair B) Chromosomal translocations C) Reduced mutation rate D) Stable karyotype Answer: B Explanation: Cancer genomes often display translocations, amplifications, and other structural changes. Question 71. Which of the following best describes the concept of “penetrance”? A) Frequency of a mutation in a population B) Proportion of carriers who express the phenotype C) Number of alleles at a locus D) Rate of gene transcription Answer: B Explanation: Penetrance quantifies how often a genotype manifests as a phenotype.
Question 77. Which of the following is a typical clinical indication for testing the CYP2D6 gene? A) Warfarin dosing B) Codeine metabolism C) Statin intolerance D) Metformin efficacy Answer: B Explanation: CYP2D6 converts codeine to morphine; variants affect analgesic response. Question 78. Which of the following best describes “gene‑environment interaction” (G×E)? A) Genes cause disease regardless of environment B) Environment solely determines phenotype C) The effect of a genotype varies with environmental exposure D) Genes and environment act independently Answer: C Explanation: G×E denotes that environmental factors modify the phenotypic impact of genetic variants. Question 79. In a double‑strand break repair, the “non‑homologous end joining” (NHEJ) pathway is characterized by: A) High fidelity B) Use of a homologous template C) Quick ligation with possible insertions/deletions D) No involvement of DNA ligase Answer: C Explanation: NHEJ rejoins ends rapidly but can introduce small indels. Question 80. Which of the following best explains why “heterozygous carriers” of a recessive disease are typically asymptomatic? A) Dominant negative effect B) One functional allele supplies sufficient protein C) Both alleles are silenced D) Epigenetic silencing of the mutant allele Answer: B Explanation: A single normal copy often produces enough functional product. Question 81. Which of the following best defines “pharmacodynamics”? A) Drug absorption B) Drug distribution C) Drug effect on the body D) Drug metabolism Answer: C Explanation: Pharmacodynamics studies the biochemical and physiological effects of drugs.
Question 82. The “CpG island” concept refers to: A) Regions rich in CG dinucleotides often unmethylated B) Protein‑coding exons C) Mitochondrial DNA repeats D) Telomeric sequences Answer: A Explanation: CpG islands are GC‑rich promoter regions commonly unmethylated in active genes. Question 83. Which of the following best describes “somatic mosaicism”? A) Uniform genotype across all cells B) Different genotypes in distinct cell populations C) Germline mutation only D) Mitochondrial inheritance only Answer: B Explanation: Somatic mosaicism arises when a mutation occurs after fertilization, creating genetically distinct cell lines. Question 84. Which of the following best explains the “founder mutation” concept in BRCA testing? A) A mutation that arises de novo in every individual B) A mutation inherited from a common ancestor prevalent in a specific population C) A mutation that only occurs in males D) A mutation that is always lethal Answer: B Explanation: Founder mutations are shared among individuals descended from a common ancestor, e.g., BRCA1 185delAG in Ashkenazi Jews. Question 85. Which of the following best characterizes “epigenetic drift” during aging? A) Increased DNA sequence mutations B) Progressive changes in DNA methylation patterns C) Stable gene expression across lifespan D) Constant telomere length Answer: B Explanation: Age‑related methylation alterations reflect epigenetic drift.
Explanation: Exon shuffling recombines coding segments, fostering novel domain architectures. Question 91. Which of the following best defines “gene‑therapy” in clinical practice? A) Use of antibiotics to alter gene expression B) Introduction of functional DNA or RNA to correct a genetic defect C) Surgical removal of mutant cells D) Dietary supplementation to change genotype Answer: B Explanation: Gene therapy delivers nucleic acids to compensate for defective genes. Question 92. Which of the following best describes a “dominant‑negative” mutation? A) A loss‑of‑function allele that interferes with the normal protein B) A gain‑of‑function allele that has no effect C) A silent mutation D) A mutation that only occurs in mitochondria Answer: A Explanation: The mutant protein antagonizes the activity of the wild‑type protein. Question 93. Which of the following best explains why “genetic counseling” is essential before predictive testing for Huntington disease? A) The test is inexpensive B) Results have no psychological impact C) The disease is autosomal recessive D) The result predicts a serious, untreatable neurodegenerative condition Answer: D Explanation: Counseling prepares individuals for the emotional and familial implications of a positive result. Question 94. Which of the following best describes “copy‑number variation” (CNV) detection using array CGH? A) Sequencing of entire genome B) Measuring fluorescence intensity differences C) PCR amplification of single loci D) Southern blot of repetitive elements Answer: B Explanation: Array comparative genomic hybridization compares sample and reference DNA fluorescence to identify gains or losses.
Question 95. Which of the following best defines “transcription factor”? A) Enzyme that replicates DNA B) Protein that binds specific DNA sequences to regulate transcription C) RNA molecule that splices introns D) Lipid that stabilizes membranes Answer: B Explanation: Transcription factors modulate gene expression by interacting with promoter/enhancer regions. Question 96. Which of the following best describes “RNA editing” in humans? A) Replacement of uracil with thymine B) Conversion of adenosine to inosine in transcripts C) Removal of introns D) Addition of poly‑A tail Answer: B Explanation: ADAR enzymes deaminate adenosine to inosine, altering codon identity. Question 97. Which of the following best explains why “heterozygous advantage” can maintain a deleterious allele in a population? A) The allele never mutates B) Carriers have increased fitness under certain conditions C) The allele is always lethal D) Random drift eliminates the allele Answer: B Explanation: Example: Sickle‑cell trait confers malaria resistance, preserving the allele. Question 98. Which of the following best describes “exome sequencing”? A) Sequencing only mitochondrial DNA B) Sequencing all coding regions of the genome C) Sequencing the entire genome D) Sequencing only non‑coding RNAs Answer: B Explanation: The exome comprises all protein‑coding exons, targeted for disease‑gene discovery. Question 99. Which of the following best characterizes “DNA barcoding” in species identification? A) Use of whole‑genome sequencing B) Sequencing a short, standardized gene region C) Measuring telomere length D) Analyzing methylation patterns Answer: B
