Complete Exam Q&A - Medical Biology Lecture

Topics: Eukaryotic Gene Expression | Pleiotropy | Complementary Genes | Polygenic Inheritance | Epistasis

SECTION 1 - EUKARYOTIC GENE EXPRESSION (Levels of Regulation)

• A) Post-translational level
• B) Translational level
• C) Transcriptional level ✅
• D) Post-transcriptional level

• A (Post-translational) - modifies already-made proteins; it's a fine-tuning step, not the primary control point.
• B (Translational) - controls how efficiently mRNA is read into protein, but this occurs after transcription is already complete.
• D (Post-transcriptional) - processes the RNA after it is made; important, but still downstream of the key decision to transcribe.

• A) RNA splicing
• B) Polyadenylation
• C) DNA methylation ✅
• D) mRNA stability control

• A, B, D - all listed in the slide as post-transcriptional mechanisms (processing RNA after it is made).

• A) Splicing and capping
• B) Phosphorylation, glycosylation, and protein degradation ✅
• C) mRNA transport out of the nucleus
• D) Ribosome binding and miRNAs

• A - post-transcriptional (RNA processing)
• C - post-transcriptional (mRNA transport)
• D - translational level (ribosome binding, miRNAs)

SECTION 2 - EPIGENETICS

• A) Regulation caused by mutations in the DNA sequence
• B) Regulation of gene expression without changes to the DNA sequence ✅
• C) Regulation involving changes in mRNA codons
• D) Regulation caused by changes in protein structure

• A - mutations are permanent changes to the DNA sequence, which is the opposite of epigenetics.
• C - mRNA codon changes would require a DNA sequence change.
• D - protein structure changes are post-translational, not epigenetic.

• A) Keeps regions inactive
• B) Permanently removes histones
• C) Unwinds DNA and promotes transcription ✅
• D) Methylates the TATA box

• A - that is the effect of histone methylation, not acetylation.
• B - histones are not permanently removed; they shift or are temporarily remodeled.
• D - the TATA box is a DNA sequence in the promoter; it is not methylated by acetylation.

• A) Activates transcription
• B) Unwinds chromatin
• C) Keeps regions inactive and prevents unwanted transcription ✅
• D) Phosphorylates RNA polymerase

• A and B - these describe the effects of acetylation, not methylation.
• D - RNA polymerase phosphorylation is a separate step in initiation complex activation.

• A) Sulfate, nitrate, and carbonyl groups
• B) Phosphate, methyl, and acetyl groups ✅
• C) Carboxyl, amino, and hydroxyl groups
• D) Lipid and sugar groups

• A, C, D - none of these are mentioned as epigenetic histone tags in the slide. These are real chemical groups but do not serve this specific histone-tagging role described here.

• A) Acetyl groups add more positive charge, attracting DNA more strongly
• B) Acetyl groups remove the histone from the nucleosome entirely
• C) Acetyl groups reduce the positive charge on histones, weakening attraction to negatively charged DNA ✅
• D) Acetyl groups cause DNA to become positively charged

• A - completely backwards; acetylation reduces, not increases, positive charge.
• B - histones are not removed; they remain as part of the nucleosome.
• D - DNA charge does not change; it is always negatively charged.

SECTION 3 - TRANSCRIPTION FACTORS AND PROMOTERS

• A) Proteins that act only in specific tissues
• B) Proteins that bind to the promoter sequence and are required for RNA polymerase II binding ✅
• C) Proteins that degrade mRNA after transcription
• D) Proteins that modify histones

• A - that describes transcription-associated factors (TAFs), which act in a time- or tissue-dependent manner.
• C - mRNA degradation is a post-transcriptional event.
• D - histone modification is an epigenetic mechanism, not the role of GTFs.

• A) A complex of ribosomes at the start codon
• B) The complex of transcription factors and RNA polymerase II assembled at the promoter ✅
• C) A complex of splicing proteins at the intron-exon junction
• D) A complex of proteins that degrade the mRNA

• A - ribosomes at the start codon describes the translation initiation complex, which is a different process.
• C - splicing is post-transcriptional.
• D - mRNA degradation happens after transcription.

• A) Shorter promoters allow more complex regulation
• B) Promoter length is identical for all genes
• C) Longer promoters provide more binding space for transcription factors, allowing more complex regulation ✅
• D) Promoter length determines the length of the mRNA

• A - backwards; longer, not shorter, promoters allow more complex regulation.
• B - the slide explicitly says promoter length is "gene-specific and can differ dramatically between genes."
• D - promoter length determines binding sites for regulatory proteins, not the length of the transcribed mRNA.

• A) A sequence coding for a structural protein
• B) A sequence of thymine and adenine repeats just upstream of the transcriptional start site where transcription factors bind ✅
• C) A sequence found only in prokaryotes
• D) The final exon of every eukaryotic gene

• A - the TATA box is a regulatory sequence, not a protein-coding region.
• C - the TATA box is a eukaryotic promoter element; prokaryotes have a Pribnow box (-10 region), not a TATA box.
• D - it is part of the promoter, upstream of where transcription starts, not a final exon.

• A) The mRNA is immediately degraded
• B) The promoter is methylated
• C) RNA polymerase binds upstream, gets phosphorylated, is released from part of the DNA, and transcription begins ✅
• D) The ribosome binds directly to the DNA

• A - mRNA degradation is a post-transcriptional event completely separate from initiation.
• B - promoter methylation is an epigenetic event that would actually silence the gene, not initiate transcription.
• D - ribosomes operate in the cytoplasm on mRNA during translation, not on DNA.

SECTION 4 - ENHANCERS AND COMBINATORIAL REGULATION

• A) Terminate transcription
• B) Code for repressor proteins
• C) Help initiate or augment transcription and can bind activator or repressor proteins ✅
• D) Remove introns from pre-mRNA

• A - termination is a separate process. Enhancers promote, not stop, transcription.
• B - enhancers are DNA sequences, not coding sequences for proteins.
• D - intron removal (splicing) is a post-transcriptional process in the nucleus.

• A) Immediately after the stop codon
• B) Inside the introns of the target gene
• C) Several thousand base pairs upstream of the target gene ✅
• D) In the 3' UTR of the mRNA

• A - upstream (before the gene), not after the stop codon.
• B - while some regulatory elements can be intronic, the slide specifically describes them as thousands of base pairs upstream.
• D - the 3' UTR is part of the mRNA (post-transcriptional), not where enhancers are located.

• A) Sequences that increase the activity of enhancers
• B) Sequences of DNA that prevent enhancers from looping to interact with the promoter ✅
• C) Sequences that code for insulating proteins in the cell membrane
• D) Sequences that protect DNA from methylation

• A - the opposite; insulators block, not increase, enhancer activity.
• C - insulators are gene regulatory elements, not sequences coding for membrane proteins.
• D - DNA methylation protection is not the function of insulators as described.

• A) Polygenic inheritance
• B) Post-translational regulation
• C) Combinatorial control of gene expression by a single transcription regulator ✅
• D) Epistasis

• A - polygenic inheritance is about multiple genes controlling one trait, not one regulator activating multiple genes.
• B - post-translational regulation involves protein modifications after synthesis.
• D - epistasis is about one gene's expression masking or modifying another gene's expression.

• A) It replaces all other transcription factors already bound
• B) It destroys inhibitory proteins
• C) It completes the required combination of regulators to strongly switch on a group of genes ✅
• D) It methylates the TATA box to silence genes

• A - it does not replace other factors; it adds to the existing assembly.
• B - no mention of destroying inhibitory proteins in this model.
• D - methylation of the TATA box would silence genes, not activate them.

SECTION 5 - POST-TRANSCRIPTIONAL REGULATION

• A) It permanently changes the DNA sequence
• B) It determines which mRNAs reach the ribosomes and how long they last, allowing one gene to produce many protein variants ✅
• C) It controls the speed of DNA replication
• D) It removes regulatory sequences from chromosomes

• A - post-transcriptional regulation does not alter the DNA sequence.
• C - DNA replication speed is controlled by replication machinery, not post-transcriptional regulation.
• D - regulatory sequences in chromosomes are a transcriptional/epigenetic concern.

SECTION 6 - PLEIOTROPY

• A) When multiple genes control one trait
• B) When one gene influences two or more different traits in the same organism ✅
• C) When a gene is expressed in only one tissue
• D) When two genes interact to produce a new phenotype

• A - multiple genes controlling one trait is polygenic inheritance.
• C - tissue-specific expression is actually the opposite of what makes pleiotropy happen; pleiotropic genes are expressed in multiple tissues.
• D - two genes producing a new phenotype together describes complementary gene interaction or epistasis.

• A) Height, bone growth, muscle development, and metabolism
• B) Skin strength, bone strength, and blood vessel walls
• C) Skin color, hair color, eye color, and UV protection ✅
• D) Insulin production, fat development, and kidney function

• A - these are effects of the growth hormone gene.
• B - these are effects of collagen genes.
• D - these relate to polygenic disorders involving metabolic genes, not melanin.

• A) Because the gene produces multiple entirely different proteins through different gene codes
• B) Because the protein it produces functions in different tissues or participates in several biological processes ✅
• C) Because mutations in it cause changes in all other genes simultaneously
• D) Because it is expressed on multiple chromosomes at the same time

• A - one gene produces one protein (or closely related variants), not multiple entirely different proteins with different functions coded separately.
• C - pleiotropy is about the reach of one protein's function, not about cascading mutations in other genes.
• D - genes are located at specific loci on specific chromosomes; they are not on multiple chromosomes simultaneously.

• A) Brain neurons and dopamine receptors
• B) Pancreatic beta cells and insulin storage
• C) Skin, bones, tendons, ligaments, and blood vessel walls ✅
• D) Eye photoreceptors and auditory hair cells

• A - neural and dopamine-related structures (relate to schizophrenia genetics, not collagen).
• B - pancreatic beta cells and insulin storage are associated with diabetes genes.
• D - photoreceptors and auditory cells are not the primary sites where collagen mutations manifest as disease.

SECTION 7 - POLYGENIC INHERITANCE

• A) One gene controlling multiple traits
• B) Two or more genes working together to control a single trait, each contributing a small additive effect ✅
• C) A single dominant gene that overrides all others
• D) Inheritance through mitochondrial DNA only

• A - one gene controlling multiple traits is pleiotropy.
• C - a single dominant gene overriding others is Mendelian dominance, not polygenic inheritance.
• D - mitochondrial inheritance is a completely separate concept involving maternal inheritance patterns.

• A) Distinct categories with no intermediate forms
• B) Either dominant or recessive with a 3:1 ratio
• C) Continuous variation (a wide range from one extreme to another) ✅
• D) Only two possible phenotypes

• A and D - discrete categories with no intermediates is the Mendelian pattern (e.g., wrinkled vs. smooth peas).
• B - the 3:1 ratio is Mendel's monohybrid ratio; polygenic traits do not follow simple Mendelian ratios.

• A) It produces insulin directly; variants destroy beta cells
• B) It regulates insulin production by pancreatic beta cells; variants increase the risk of reduced insulin production ✅
• C) It encodes angiotensin-converting enzyme; variants raise blood pressure
• D) It breaks down dopamine; variants cause insulin resistance

• A - TCF7L2 regulates insulin production, not produces insulin itself; it does not destroy beta cells directly.
• C - ACE (angiotensin-converting enzyme) is a hypertension gene, not a diabetes gene.
• D - COMT breaks down dopamine and is associated with schizophrenia, not insulin resistance.

• A) ACE; it narrows blood vessels
• B) AGT; it raises blood pressure
• C) NOS3; it relaxes blood vessels ✅
• D) AGTR1; it encodes the angiotensin II receptor

• A - ACE produces angiotensin-converting enzyme (a vasoconstrictor pathway gene), not nitric oxide.
• B - AGT produces angiotensinogen, a protein involved in narrowing blood vessels.
• D - AGTR1 encodes the receptor for angiotensin II. All three of these (ACE, AGT, AGTR1) are hypertension genes, but they do not produce nitric oxide.

• A) Controls calcium channels important for neuron function
• B) Supports brain development and nerve signaling
• C) Breaks down dopamine in the brain ✅
• D) Encodes the dopamine D2 receptor

• A - CACNA1C controls calcium channels.
• B - NRG1 supports brain development and nerve signaling.
• D - DRD2 encodes the dopamine D2 receptor. All are real schizophrenia-associated genes, but none of them breaks down dopamine - that specific function belongs to COMT.

• A) Genes have no role in polygenic traits
• B) The phenotype is determined solely by environment
• C) The final phenotype is the combined result of multiple gene effects plus environmental influences ✅
• D) Polygenic traits are immune to mutation

• A and B - neither genes alone nor environment alone determines the phenotype; it is their combination.
• D - polygenic traits are absolutely subject to mutation; in fact, variants in the contributing genes are what drive disease risk.

SECTION 8 - COMPLEMENTARY GENE INTERACTION

• A) Two genes that each independently produce the same trait
• B) Two different genes that must BOTH have at least one dominant allele to produce the dominant phenotype ✅
• C) One gene completely blocking the expression of another
• D) A gene that produces multiple traits simultaneously

• A - independently producing the same trait would not create the 9:7 ratio; both must contribute together.
• C - one gene blocking another describes epistasis (recessive epistasis specifically), not complementary interaction.
• D - one gene producing multiple traits is pleiotropy.

• A) Both enzymes are present, flowers are purple
• B) Enzyme 1 is missing (from gene C), the pathway stops, flowers are white ✅
• C) Enzyme 2 is missing (from gene P), flowers are red
• D) Both enzymes are missing, flowers are pink

• A - if cc, then gene C cannot produce Enzyme 1, so the pathway is broken.
• C - red flowers are not mentioned in this example; the only outcomes are purple (C_P_) or white (anything else).
• D - even one recessive homozygous gene is enough to stop the pathway; the result is white flowers, but the specific enzyme missing depends on which gene is cc or pp.

• A) 9:3:3:1
• B) 12:3:1
• C) 9:7 ✅
• D) 3:1

• A (9:3:3:1) - this is the standard dihybrid ratio when the two genes independently control separate traits with no interaction.
• B (12:3:1) - this is the ratio for dominant epistasis.
• D (3:1) - this is the monohybrid ratio for a single gene with complete dominance.

SECTION 9 - EPISTASIS

• A) When one gene produces two different proteins
• B) When the phenotypic expression of one gene depends on the presence or absence of variants in another gene ✅
• C) When two genes on the same chromosome are always inherited together
• D) When a gene is expressed only during embryonic development

• A - one gene producing two proteins relates to alternative splicing or post-translational processing, not epistasis.
• C - genes on the same chromosome being inherited together is called genetic linkage.
• D - stage-specific expression is temporal gene regulation, not epistasis.

• A) Dominant gene and recessive gene
• B) Epistatic gene (modifies/masks) and hypostatic gene (is affected) ✅
• C) Activator gene and suppressor gene
• D) Promoter gene and enhancer gene

• A - dominant/recessive describes allele relationships within one gene, not gene-gene interaction.
• C - activator and suppressor are informal terms used loosely but not the formal terminology for epistasis.
• D - promoters and enhancers are DNA sequences, not genes that mask each other.

• A) Only enzymes in metabolic pathways
• B) Only transcription factors
• C) Enzymes, transcription factors, cell signaling proteins, DNA repair mechanisms, immune response pathways, and protein-protein interactions ✅
• D) Only protein-protein interactions

• A, B, D - each picks only one category. The slide makes clear that epistasis operates through multiple molecular mechanisms simultaneously.

• A) The CFTR mutation is not the real cause of cystic fibrosis
• B) Different patients have different amounts of CFTR protein
• C) Modifier genes involved in inflammation, mucus clearance, and immune function alter disease progression through epistatic interactions ✅
• D) Environmental factors alone explain the difference

• A - CFTR mutations are definitively the primary cause; the point is about variation in severity, not cause.
• B - different CFTR protein amounts could contribute, but the slide specifically attributes the variation to modifier genes (epistasis), not CFTR expression levels.
• D - while environment plays a role, the slide specifically identifies genetic modifiers (epistasis) as the explanation in this context.

• A) Higher HbF worsens sickle cell disease by competing with normal hemoglobin
• B) HbF has no effect on sickle cell disease severity
• C) Variants that increase HbF production reduce the severity of sickle cell disease, illustrating epistatic interaction ✅
• D) HbF production is controlled by the same HBB gene mutation that causes sickle cell disease

• A - completely backwards; higher HbF is protective and beneficial in sickle cell disease.
• B - HbF has a well-documented and clinically significant effect on sickle cell severity.
• D - HbF is encoded by a separate fetal globin gene (HBG), not the HBB gene where the sickle mutation occurs.

• A) Epistasis has no role in drug response
• B) Epistasis is only relevant to rare single-gene disorders
• C) Interactions among genes encoding drug-metabolizing enzymes, transport proteins, and drug targets help determine optimal drug selection and dosage ✅
• D) Precision medicine only uses environmental data, not genetic interactions

• A - entirely wrong; the slide explicitly identifies epistasis as a key factor in pharmacogenomics.
• B - epistasis is emphasized in the slide specifically for complex, multifactorial diseases, not just rare single-gene disorders.
• D - precision medicine integrates genetic interaction data (including epistasis) as a core component.

• A) Epistasis only matters after cancer has already developed
• B) Interactions among tumor suppressor genes, oncogenes, and DNA repair genes influence cancer initiation, progression, and treatment response ✅
• C) All cancer risk is determined by a single dominant oncogene
• D) Epistasis prevents DNA repair genes from functioning

• A - epistasis affects both initiation and progression, not just post-development behavior.
• C - cancer is a multifactorial, multigenic process; no single oncogene determines all cancer risk.
• D - the slide describes DNA repair genes as participants in epistatic networks, not as being prevented from functioning by epistasis.

• A) Epistasis is only relevant in agricultural genetics
• B) Epistasis explains why identical twins always have identical diseases
• C) Epistasis contributes to variable disease penetrance, differences in severity among patients with the same mutation, individual susceptibility, variability in drug response, and identification of genetic modifiers ✅
• D) Epistasis causes new mutations to arise in somatic cells

• A - the entire slide explicitly discusses epistasis in human medicine - cancer, sickle cell, cystic fibrosis, schizophrenia.
• B - identical twins can have different disease expression precisely because of epistatic and epigenetic variation.
• D - epistasis describes gene-gene interactions influencing expression, not a mechanism that creates new mutations.

SECTION 10 - HIGH-DIFFICULTY INTEGRATION QUESTIONS

• A) Polygenic inheritance
• B) Pleiotropy ✅
• C) Complementary gene interaction
• D) Epistasis

• A - polygenic = multiple genes → one trait (the reverse).
• C - complementary interaction requires two genes working together to produce ONE trait.
• D - epistasis involves one gene masking/modifying another gene's expression.

• A) Epistasis
• B) Polygenic inheritance
• C) Complementary gene interaction ✅
• D) Pleiotropy

• A - epistasis produces ratios like 12:3:1 or 9:3:4, not 9:7.
• B - polygenic inheritance produces continuous variation, not clean Mendelian ratios.
• D - pleiotropy is about one gene affecting many traits, not two genes required for one trait.

• A) Pleiotropy
• B) Complementary gene interaction
• C) Epistasis ✅
• D) Post-translational regulation

• A - pleiotropy is one gene affecting multiple traits, not two genes interacting to affect blood pressure severity.
• B - complementary gene interaction requires BOTH dominant alleles to produce the dominant phenotype; here both variants are harmful rather than one being required for a beneficial product.
• D - post-translational regulation is about protein modifications after synthesis, not gene-gene interaction at the population/phenotype level.

• A) Polygenic interaction
• B) Epigenetic regulation through loss of acetylation, leaving histones with high positive charge that tightly attracts the negatively charged DNA ✅
• C) Complementary gene interaction
• D) Epistasis through protein-protein interaction

• A - polygenic interaction is about multiple genes controlling one trait, not chromatin structure.
• C - complementary gene interaction is about two genes needing dominant alleles to produce a phenotype.
• D - while epistasis can involve DNA repair pathways, the mechanism asked about here is specifically chromatin compaction by unacetylated histones.

• A) A pleiotropic gene because it affects multiple pathways
• B) The hypostatic gene in an epistatic interaction
• C) The epistatic gene (modifier) that increases the penetrance of the BRCA1 mutation ✅
• D) A complementary gene required for tumor suppressor function

• A - while BRCA1 may be pleiotropic, the DNA repair gene in this question is acting as a modifier (epistatic), not as a pleiotropic gene.
• B - hypostatic is the gene that IS affected by the epistatic gene. Here BRCA1 is the hypostatic gene (its expression/effect is being modified); the DNA repair gene is the epistatic one.
• D - complementary gene interaction requires both dominant alleles for a phenotype. Here we are talking about increasing penetrance of a disease allele, which is epistasis.

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