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You will find below a question bank containing 65 questions to help you to ascertain the effectiveness of your review. These are organized under general groupings that correspond to specific MCAT (Medical College Admissions Test) categories. In turn, you can consider this as a list of topics from MCAT that we are expecting students to bring to medical school in terms of proficiency. With a 65-question pool, you might be able to test yourself twice; for example, one test containing all the odd-numbered questions and a second test containing all the even-numbered questions. We would suggest that you do this under “testing conditions”: one hour for each test (approximately 2 minutes per question); no looking up the answers until you have completed each test. In a separate file, we have provided the Answer Key to the 65 questions. You should regard a score of 70% as minimum proficiency. 15 questions covering the following MCAT categories 1A Structure and function of proteins and their constituent amino acids Amino acids; protein structure; non-enzymatic protein function; enzyme structure and function; control of enzyme activity 2A Assemblies of molecules and groups of cells in eukaryotes Plasma membrane; membrane-bound organelles; cytoskeleton 5A Nature of aqueous solutions General chemistry (solubility; ions in solution; acid-base; titration) 5B Molecular interactions General chemistry (covalent bonds; H-bond; dipole interactions; van der Waals forces) 5D Structure and function of biologically relevant molecules Organic chemistry (functional groups: aldehydes and ketones; alcohols; carboxylic acids and derivatives such as anhydrides, esters, and amides; phenols and aromatic compounds); biochemistry (carbohydrates; amino acids and proteins; nucleic acids; lipids) 5E Thermodynamics and kinetics General chemistry (thermodynamics and kinetics); biochemistry (enzymes and bioenergetics) 1) The structural formula for a molecule is given below. How many peptide bonds does this molecule have?

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A) 0 B) 2 C) 3 D) 4 E) 5 2) The structural formula for a molecule is given below. Considering only the side chains of the amino acids in this molecule, which of the following can participate in a hydrogen bond with water?

A) amino acid #1 B) amino acid #3 C) amino acid #5 D) all E) none 3) The structural formula for a molecule is given below. Considering only the side chains of the amino acids in this molecule (for which a pKa table is provided), which of the following can become positively charged at pH 7.4?

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A) amino acid #1 B) amino acid #2 C) amino acid #3 D) amino acid #4 E) amino acid #5

4) The structural formula for a molecule is given below. The covalent bond directly linking atoms in residues 1 and 6 is:

A) a disulfide bond B) a hydrogen bond C) a hydrophobic bond D) a peptide bond E) a salt bridge

5) Normal mammalian cell membranes:

A) have inner and outer leaflets that are identical in composition B) are covalent assemblies of phospholipids C) contain proteins, called peripheral proteins, that span the bilayer D) contain triacylglycerols as their primary lipid component E) utilize cholesterol to help maintain their fluid-like properties

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6) Membrane lipids are amphipathic. By this, we mean:

A) They all contain head groups with a net charge B) They can interact with integral as well as peripheral membrane proteins C) They all contain polar head groups D) They all contain polar head groups as well as hydrophobic tails. E) They all contain head groups with a net charge and hydrophobic tail groups.

7) Which of the following best represents the relative sizes of the cytoskeletal structures of mammalian cells, from the largest in diameter to the smallest in diameter?

A) Microtubules > Intermediate Filaments > Microfilaments B) Intermediate Filaments > Microfilaments > Microtubules C) Microfilaments > Microtubules > Intermediate Filaments D) Intermediate Filaments > Microtubules > Microfilaments E) Microtubules > Microfilaments > Intermediate Filaments

8) Which series of compounds is listed in order from the most reduced state to the most oxidized state? A) an acid, a ketone, an alcohol, and an alkane B) an alkane, an alkene, an acid, and an aldehyde C) an acid, an alkane, an alcohol, and an aldehyde D) an alkane, an alcohol, an aldehyde, and an acid E) an alkene, an acid, an aldehyde, and an alcohol 9) For this question, use the graph below which shows the changes in free energy when a reactant is converted to a product in the presence and absence of an enzyme. Select the letter that best represents the free energy of activation of the enzyme-catalyzed forward reaction.

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10) This question refers to the chemical reaction shown below. Data for the key reaction parameters in the absence of any enzyme are also provided. If you were to add an enzyme to speed up the reaction, what type of enzyme would carry out this reaction? ΔG’= +0.6 kcal/mol EA = 25 kcal/mol V = 2.1 x 10-7 sec-1 Keq = 0.05 A) Epimerase B) Isomerase C) Dehydrogenase D) Kinase E) Hydrolase 11) This question refers to the chemical reaction shown below. Data for the key reaction parameters in the absence of any enzyme are also provided. Which of the following correctly notes the changes that would occur to these parameters in the presence of the appropriate enzyme? ΔG’= +0.6 kcal/mol EA = 25 kcal/mol V = 2.1 x 10-7 sec-1 Keq = 0.05

A) ΔG’ is lowered to a negative value in order to make the reaction thermodynamically favorable.

B) EA is lowered in order to make the transition state more easily reached. C) V is unchanged by the enzyme. D) Keq is increased in order to have more of the product at equilibrium

O

HC

CH OH

CH2OPO32-

CH2OH

CH2OPO32-

C O

1 2

O

HC

CH OH

CH2OPO32-

CH2OH

CH2OPO32-

C O

1 2

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12) Asparaginase is used to reduce the level of asparagine in the blood in one treatment for leukemia. Which isozyme of asparaginase would be most useful if the patient’s blood asparagine level is 0.2 mM? Km Vmax A) 0.1mM; 0.5 mM/hr B) 0.2mM; 0.1 mM/hr C) 0.2mM; 0.5 mM/hr D) 2.0mM; 0.1 mM/hr E) 0.1mM; 0.1 mM/hr 13) Oxygen Spartan Village Vail Ski Resort Pressure East Lansing, MI Vail, CO ambient pO2 159 mm Hg 95 mm Hg tracheal pO2 149 86 alveolar pO2 105 50 arterial pO2 100 45 Information on oxygen pressures are provided above for Michigan and Colorado. You leave East Lansing for a holiday skiing trip. Two days after arriving at Vail, the best prediction for [2,3-bisphosphoglycerate] and the P50 for hemoglobin binding to oxygen in your body is: The symbols, ↑, ↓, and ↔ represent increase, decrease, and remain the same, relative to Michigan. [2,3-bisphosphoglycerate] P50 (mmHg) A) ↑ ↑ B) ↑ ↓ C) ↔ ↔ D) ↓ ↓ E) ↓ ↑ 14) Several oxygen saturation curves are shown in the figure below. Assuming that curve 3 corresponds to data obtained from venous blood perfusing the skeletal muscle at rest, which of the curves would most closely reflect the corresponding data during exercise?

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A) Curve 1 B) Curve 2 C) Curve 3 D) Curve 4 15) The main reason for treating severe carbon monoxide poisoning by placing the affected individual in an oxygen tent is: A) The individual has difficulty breathing. B) Carbon monoxide poisons oxygen transport across the alveoli of the lung. C) Carbon monoxide is a competitive inhibitor of oxygen binding to hemoglobin. D) Carbon monoxide combines with oxygen to form carbon dioxide (CO + O2 —► CO2) and this production of non-toxic carbon dioxide reduces the concentration of the poison. E) In the presence of CO, the heme prosthetic group can form a "sandwich," resulting in the oxidation of iron (Fe+2 —► Fe+3). 30 questions covering the following MCAT categories 1D Principles of bioenergetics and fuel metabolism Bioenergetics principles; carbohydrate metabolism (glycolysis; GNG; PPP); TCA cycle and oxidative phosphorylation; fatty acid metabolism; protein metabolism; hormonal regulation and integration of metabolism 3A Structure and function of nervous and endocrine systems and their coordination Nerve cells and nervous system; Nernst equation; biosignaling (ion channels and G-protein coupled receptors); hormones and second messengers; steroid hormones 5D Structure and function of biologically relevant molecules Organic chemistry (functional groups: aldehydes and ketones; alcohols; carboxylic acids and derivatives such as anhydrides, esters, and amides; phenols and aromatic compounds); biochemistry (carbohydrates; amino acids and proteins; nucleic acids; lipids)

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16) ATP, acetyl-CoA and nicotinamide adenine dinucleotide (NAD) share many structural and functional properties. Which of the following statements is TRUE about ATP, acetyl-CoA and NAD?

A) They can all be described as B vitamins. B) They all contain a pyranose sugar. C) They all contain an adenine base. D) They can all act as a carrier of carbon chains. E) They all utilize a thiol group at the active site.

17) The importance of pantothenic acid in metabolism cannot be overstated. Which of the following statements best describes pantothenic acid?

A) Its coenzyme derivative is nicotinamide adenine dinucleotide B) The active site of its coenzyme derivative is a thiol group C) The structure does not contain a nitrogenous base D) It is a carrier of hydrogen produced during the breakdown of sugars E) Deficiencies lead to a condition known as glossitis

18) Which statement best describes the structure labeled I?

A) It contains a pyranose sugar B) It is one of four bases used as direct precursors to DNA C) It contains a pyrimidine structure D) It is a nucleoside E) It contains adenine as a nitrogenous base

19) You have just eaten some chocolate covered sugar O’s for breakfast. Which of the following enzymes serves to protect your system from a dangerous spike in blood sugar after this meal? A) Fructokinase B) Glucokinase C) Hexokinase D) Galactokinase E) Phosphofructokinase 20) A medical student has been studying so intensively he has gone without food for 24 hours. The major source of fuel for his brain will now be from

A) glycogen breakdown in muscle B) ketone bodies from the liver C) gluconeogenesis in the liver D) β-oxidation of fatty acids E) amino acid degradation

H

O

HH

OHOH

H

CH2

N

NCC NC

C NHC H

NH2

OPO

O-OP

O

O-OP

O-O

O-

Structure I

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21) In a person with a deficiency of fructose 1,6-bisphosphatase, the predominant metabolic consequence is: A) failure to synthesize glucose from lactic acid B) failure to split fructose 1,6-bisphosphate into triose phosphates C) inability to degrade glycogen D) inability to fix CO2 into organic linkages E) lowered yield of ATP production per mole of glucose metabolized 22) Which of the following is NOT a fate of the molecule shown below? A) acetoacetyl CoA B) malonyl CoA C) citrate D) pyruvate 23) Which of the following enzymes catalyzes the reaction,

A) Acetyl CoA carboxylase B) Pyruvate carboxylase C) Pyruvate dehydrogenase D) Pyruvate kinase E) β-ketothiolase (3-ketothiolase)

24) Which of the molecules shown below can ultimately be synthesized from acetyl CoA?

A) Molecules 1 and 2 only B) Molecules 2 and 4 only C) Molecules 1, 2, and 3 only D) Molecules 1, 2, and 4 only E) Molecules 1, 2, 3, and 4

CH3 C

O

SCoA

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25) Which of the following best describes the primary function of the Pentose Phosphate Pathway?

A) To supply ATP to cells in anaerobic conditions B) To supply NADH for electron transport C) To provide precursors and reducing power for anabolic processes D) To oxidize NADPH so that glycolysis can continue

26) Vitamin deficiencies may affect many metabolic pathways due to the requirement of cofactors in enzymatic reactions. The Pentose Phosphate Pathway (PPP) can be run in one of four modes, depending on the specific purpose or product(s) needed (listed below). Which of these four modes of the PPP would NOT be affected by thiamine deficiency? Mode #1: NADPH + Ribose-5-P Mode #2: NADPH only Mode #3: NADPH + energy Mode #4: Ribose 5-P only

A) Mode 1 B) Mode 2 C) Mode 3 D) Mode 4 E) All modes

27) What three metabolites are common to glycolysis and the pentose phosphate pathway? A) glucose 6-phosphate, fructose 6-phosphate, and pyruvate B) glucose 6-phosphate, glyceraldehyde 3-phosphate, and pyruvate C) fructose 6-phosphate, glyceraldehyde 3-phosphate, and phosphoenolpyruvate D) fructose 1,6-bisphosphate, glyceraldehyde 3-phosphate, and 6-phosphoglucolactone E) glucose 6-phosphate, fructose 6-phosphate, and glyceraldehyde 3-phosphate 28) Which of the following correctly describes a functioning mitochondrion?

A) Will use oxygen at a constant rate regardless of ADP levels. B) Will have the same P/O ratio for NADH and FADH2

CH3 (CH2)14 C

O

O-

HO

O

C

CC

C

CH

CH2OH

H

OH

H

OH H

OH

H

OH

CH3

O

C CH2 C

O

O-

1

2

3

4

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C) When thermogenin (aka UCP1) is activated, ATP generation will decrease D) In the presence of oligomycin, the membrane potential will drop E) In the presence of 2,4 dinitrophenol oxygen consumption will decrease

29) At very high doses, the cholesterol lowering drug Lipitor would lead to an almost complete

loss of CoQ (also known as CoQ10 and ubiquinol). Given the relationship between the function of the electron transport chain and the utilization of reducing equivalents, what glycolytic enzyme would most directly be affected by mitochondrial dysfunction caused by the loss of CoQ?

A) Phosphofructokinase 1 B) Glyceraldehyde 3-phosphate dehydrogenase C) Phosphoglycerate kinase D) Glucokinase E) Enolase

30) Which of the following compounds is permeable to the inner mitochondrial membrane and serves as a shuttle for reducing equivalents from the cytosol into the mitochondria? A) Succinate B) NADH C) Oxaloacetate D) Malate E) ADP 31) For oxaloacetate to be used in gluconeogenesis, it must first be transported across the inner mitochondrial membrane in the form of: A) oxaloacetate B) citrate C) malate D) aspartate E) glycerol 32) What are the products of beta-oxidation of a C15 fatty acid? A) 7 acetyl CoA, 6 (NADH + H+), 6 FADH2 B) 1 propionyl CoA, 6 acetyl CoA, 6 (NADH + H+), 6 FADH2 C) 2 propionyl CoA, 5 acetyl CoA, 4 (NADH + H+), 4 FADH2 D) 1 propionyl CoA, 7 acetyl CoA, 7 (NADH + H+), 7 FADH2 E) 1 propionyl CoA, 7 acetyl CoA, 8 (NADH + H+), 8 FADH2 33) Which of the following statements correctly describes fatty acid synthesis and β-oxidation of fatty acids?

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A) Fatty acid synthesis intermediates are covalently linked to coenzyme A (CoA), while β-oxidation intermediates are linked to an acyl carrier protein (ACP). B) Fatty acid synthesis occurs in the mitochondrial matrix and β-oxidation occurs in the cytosol of all cells. C) The carboxylation of acetyl CoA to malonyl CoA is the committed step in β-oxidation of fatty acids. D) The fatty acid chain is elongated by the sequential addition of 3 carbon units during fatty acid synthesis. E) NADPH is a cofactor used in fatty acid synthesis, while NAD+ and FAD are used in β-oxidation. 34) Put the following molecules (A, N, T, Y) in order, from the most oxidized to the most reduced.

A) molecule N, molecule T, molecule Y, molecule A B) molecule A, molecule N, molecule Y, molecule T C) molecule T, molecule N, molecule Y, molecule A D) molecule T, molecule Y, molecule N, molecule A E) molecule A, molecule Y, molecule N, molecule T

35) Which of the following are all POSITIVE regulators of fatty acid synthesis? A) ATP, citrate, glucagon

B) Insulin, citrate, ATP C) Palmitoyl CoA, AMP, insulin D) Glucagon, epinephrine, citrate E) Palmitoyl CoA, AMP, glucagon

36) What is the "activated" form of glucose used during the lengthening of a glycogen primer? A) ATP- glucose B) pyrophosphate C) CDP-glucose D) malonyl Co-A

C H 3 C C

H

H

C

O

S A C P

C H 3 C

O

C H 2 C

O

S A C P

C H 3 C H 2 C H 2 C

O

S A C P

C H 3 C H 2 C

O

S A C PC

O H

H

m o le c u le N

m o le c u le T

m o le c u le A

m o le c u le Y

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E) UDP-glucose 37) A long distance runner is several hours into a race. His metabolism is dominated by the influence of epinephrine and glucagon. Which of the following correctly describes metabolism occurring in the liver, muscle, and adipose tissue? A) Concentrations of cAMP are decreased in both the liver and muscle. B) Muscle tissue increases glucose uptake from the blood. C) HMG CoA reductase is active in the liver. D) Glycogen phosphorylase is phosphorylated and active in both liver and muscle. E) Triacylglycerol breakdown is inhibited in adipose tissue. 38) Ketone bodies can NOT be used for energy by A) skeletal muscle cells B) kidney cells C) brain cells D) red blood cells E) cardiac muscle cells 39) After five weeks of starvation, which of the following statements would correctly describe the changes in levels of circulating fuel compared to the well-fed state? A) lactate, pyruvate, and alanine are higher B) glucose is higher C) overall ATP equivalents of circulating fuel is lower D) fatty acids are higher E) ketone bodies are lower 40) An insulinoma is a type of pancreatic tumor that results in increased insulin production. Which of the following would most likely be seen in an untreated patient with an insulinoma? A) increased serum fatty acids B) polyuria (frequent urination) C) reduced liver glycogen stores D) ketosis E) hypoglycemia 41) When plasma glucose concentration increases above normal, beta cells of the pancreas respond

by secreting insulin into the blood stream. In the liver, insulin activates insulin receptors on cell membranes of hepatocytes. This causes an increase in the production of glucokinase (an enzyme in the glycolysis reaction sequence). Which of the following (A – E) correctly identifies the endocrine "first messenger" in this signaling pathway?

A) glucose B) pancreatic beta-cells

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C) insulin D) insulin receptors E) glucokinase

42) A healthy 14-year old boy is brought to the clinic for a routine check-up. History and

physical exam indicate that his sexual development is normal for his age. These pubertal changes are most likely due to the binding of androgen to its receptor. This hormone receptor complex will exert its final effect in the:

A) Endoplasmic reticulum B) Golgi C) Mitochondria D) Nucleus E) Plasma membrane

43) Which of the following is TRUE for cyclic AMP?

A) is increased by activation of Gi protein B) inhibits C-kinase (PKC) C) is increased by activation of Gs protein D) is transformed into phosphodiesterase E) is increased by activation of Gq protein

44) Endogenous protein degradation in the body

A) is catalyzed entirely by the ubiquitin-dependent pathway. B) results in production of free amino acids which are stored in a large amino acid pool that is available for synthesis. C) accomplishes the changes in metabolism necessary to deal with changes in nutrient intake. D) occurs at about the same rate for every enzyme or protein in the body. E) is always an energy-independent process.

45) Digestion and absorption of proteins:

A) requires amylases. B) is more effective if the protein has a high content of essential amino acids C) occurs by hydrolysis of peptide bonds by proteases that are stored as zymogens D) occurs only by removal of amino acids from the ends of chains (N-terminal or C-terminal) E) does not occur in the stomach.

20 questions covering the following MCAT categories 1B Transmission of genetic information from gene to protein Nucleic acids structure and function; DNA replication; repair of DNA; genetic code; transcription; translation; eukaryotic chromosome organization; control of gene expression in prokaryotes; control of gene expression in eukaryotes; Recombinant DNA technology

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1C Transmission of genetic information from generation to generation Mendelian concepts (gene; locus; alleles; homozygote versus heterozygote; dominant versus recessive); meiosis and other processes affecting genetic variability; analytic methods (e.g. Hardy-Weinberg)

46) Which of the above structures labeled A-E would be found in a eukaryotic mRNA? 47) The structure shown below is a segment of a nucleotide. This segment depicts the codon for which of the following amino acids?

A) Isoleucine (Ile) B) Leucine (Leu) C) Methionine (Met) D) Phenylalanine (Ala) E) Valine (Val)

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48) The diagram below schematically illustrates a eukaryotic transcription bubble, in which RNA polymerase is transcribing a single-stranded RNA on the basis of the sequence of nucleotides on the template strand of the double-stranded DNA. Which letter (A - E) marks the 5'-end of the template strand?

49) A 5-year-old girl presents with basal and squamous cell carcinomas, predominantly on the face, head, and neck. Clinical tests confirm the suspected diagnosis of xeroderma pigmentosum (XP). Cells from individuals with XP have elevated mutation rates due to a deficiency in the ability to correct UV-induced damage. Which segment of DNA is most likely to be mutated in this patient? A) GCATATGC B) ATTCGCAT C) GTACGTAC D) GCGCGCGC E) ATATATAT 50) Mutations causing xeroderma pigmentosum (XP) reside in any of several proteins required for A) mismatch repair. B) nucleotide excision repair. C) base excision repair. D) recombination repair. 51) Each year, more than 100 people worldwide die after eating poisonous mushrooms. The death cap mushroom, Amanita, produces a toxin which strongly binds to and inhibits RNA polymerase II, thereby blocking: A) proofreading during transcription B) recognition of the TATA box promoter element C) production of tRNA D) production of mRNA E) recognition of the polyadenylation signal

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52) The most likely consequence of a mutation present at the location indicated by the arrow in the above mRNA schematic would be: A) An amino acid change in the encoded protein B) None; this region of mRNA has no function C) Abberant splicing of the mRNA D) Ubiquitinylation and subsequent degradation E) Altered response to regulatory factors 53) Bacterial mRNAs contain: A) Only one open reading frame B) Formyl-methionine C) 7-methyl-guanosine D) Sequence specific ribosomal binding sites E) The modified base, pseudouracil 54) A 4 yr old female presents with an insatiable appetite and morbid obesity. Genetic analysis shows that the patient’s gene for the appetite control hormone, leptin, contains a mutation in its promoter region that decreases TFII-D binding. What is the most likely effect of this mutation? A) Capping of the leptin mRNA will be defective. B) Splicing of the leptin mRNA will be defective. C) Initiation of leptin transcription will be defective. D) Termination of leptin transcription will be defective. E) Secretion of the leptin peptide will be defective. 55) The BRCA1 gene, which influences susceptibility to breast and ovarian cancer, is very large, spanning roughly 100,000 base pairs of DNA. However, the mRNA from this gene is only 7,800 bases long. This difference is best explained by: A) the gene encodes a polycistronic mRNA B) the size of the mRNA is reduced by site-specific recombination C) unneeded regions of the RNA at the 5'- and 3'-ends are removed by endonucleases D) the primary transcript is spliced to remove many large introns E) only a small region of the gene is transcribed. 56) Which of the following will be used during the translation of the BRCA1 gene product (protein) in human breast cells?

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A) polycistronic mRNA B) N-formylmethionine tRNA C) a tRNA with a 5'-UUA anticodon D) 16S ribosomal RNA E) 5'-cap nucleotide on the mRNA 57) The following terms refer to human nuclear material. Arrange them in order of increasing size and structural complexity: A) nucleoside, nucleotide, chromatin, nucleosome, genome, chromosome B) nucleotide, nucleoside, chromatin, nucleosome, chromosome, genome C) nucleoside, nucleosome, nucleotide, chromosome, chromatin, genome D) nucleoside, nucleotide, nucleosome, chromatin, chromosome, genome E) chromosome, genome, chromatin, nucleosome, nucleotide, nucleoside 58) Regarding the stages of mitosis and meiosis at which the centromeres split, which of the following is TRUE? Mitosis Meiosis A) prophase metaphase I B) telophase anaphase I C) anaphase anaphase I D) anaphase anaphase II E) metaphase telophase II 59) Which of the following karyotypes is an example of euploidy? A) 47,XXX B) 45,X C) 68,XXX,-21 D) 92,XXXX E) 48,XX,+21,+22 60) Which of the following represents a BALANCED chromosomal rearrangement?

A) A ring chromosome B) An isochromosome C) A chromosome with a deletion D) A chromosome with a duplication E) A chromosome with an inversion

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61) An example of a typical normal male karyogram is shown above. The chromosome number is indicated below each homologous pair and the location of the centromere is indicated by the dotted line. Which of the following is an acrocentric chromosome?

A) chromosome 20 B) chromosome 3 C) chromosome 17 D) chromosome 13 E) X chromosome

62) A man with craniofrontonasal dysplasia, an X-linked dominant condition, wants to know his chance of having an affected daughter. The BEST response is: A) 0% B) 25%

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C) 50% D) 100% 63) What is the most likely mode of inheritance depicted in the pedigree below?

A. Autosomal dominant B. Autosomal recessive C. Mitochondrial (maternal) D. X-linked dominant E. X-linked recessive

64) You are an internist seeing an adult patient for the first time. She has two sisters and two brothers. She and all of her siblings have the combination of lactic acidosis, stroke-like episodes, and various neurologic disorders. Her sisters both have several children of both sexes with the same condition, whereas her brothers’ children are all unaffected. The MOST likely mode of inheritance for this condition is: A) autosomal dominant B) X-linked dominant C) X-linked recessive D) mitochondrial E) Y-linked 65) A woman whose two siblings had Bloom syndrome (manifestations include growth deficiency and immunodeficiency) an autosomal recessive condition, wants to know her chance of having a similarly affected child. The general population carrier frequency is approximately 1/100. She is not related to her spouse. The BEST estimate of risk is: A) 1/300 B) 1/400 C) 1/600 D) 1/800