Molecular Basis of Inheritance MCQ. Study MCQs on Molecular Basis of Inheritance: DNA structure, replication, transcription, translation, genetic code, and applications.
Molecular Basis of Inheritance MCQ – Mock Online Test
Question 1: Which of the following is a pyrimidine base found in DNA?
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Correct Answer: C. Thymine. Adenine and Guanine are purines, while Uracil is a pyrimidine found in RNA, not DNA.
Question 2: What type of bond links the nitrogenous base to the pentose sugar in a nucleotide?
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Correct Answer: C. N-glycosidic bond. Phosphodiester bonds link nucleotides together, hydrogen bonds connect base pairs, and peptide bonds join amino acids in proteins.
Question 3: What is the difference between the 5′ and 3′ ends of a DNA strand?
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Correct Answer: B. The 5′ end has a free phosphate group, while the 3′ end has a free hydroxyl group. This directionality is crucial for DNA replication and transcription.
Question 4: Which of the following is NOT a characteristic of DNA?
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Correct Answer: C. Contains uracil. Uracil is found in RNA; DNA contains thymine instead.
Question 5: What is the function of histone proteins in DNA packaging?
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Correct Answer: C. They help to coil and condense DNA into chromosomes. Histones are positively charged proteins that bind to negatively charged DNA, allowing it to be tightly packed.
Question 6: What is the name of the structure formed when DNA is wrapped around a histone octamer?
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Correct Answer: A. Nucleosome. Chromatin is a complex of DNA and proteins, including histones, that make up chromosomes. The nucleoid is the region where DNA is located in prokaryotes.
Question 7: What is the difference between euchromatin and heterochromatin?
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Correct Answer: B. Euchromatin is loosely packed and transcriptionally active, while heterochromatin is tightly packed and transcriptionally inactive.
Question 8: Which of the following is NOT true about the length of DNA?
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Correct Answer: C. A bacteriophage has more base pairs than E. coli. E. coli has a larger genome than a bacteriophage.
Question 9: How is DNA organized in prokaryotes?
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Correct Answer: A. In large loops held by proteins in a region called the nucleoid. Prokaryotes lack a defined nucleus.
Question 10: Which amino acids are histone proteins rich in?
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Correct Answer: A. Lysine and arginine. These amino acids have positively charged side chains that help histones bind to negatively charged DNA.
Question 11: Which of the following is NOT a criterion for a molecule to act as genetic material?
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Correct Answer: D. It should be composed of both DNA and RNA. Genetic material can be either DNA or RNA, but not necessarily both.
Question 12: Which of the following is NOT true regarding Griffith’s experiments with Streptococcus pneumoniae?
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Correct Answer: B. Mice infected with the heat-killed rough strain die from pneumonia. The rough strain is non-virulent, and heat-killing the virulent smooth strain makes it non-lethal unless mixed with live rough strain.
Question 13: What was the conclusion of Avery, MacLeod, and McCarty’s experiments?
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Correct Answer: C. DNA is the genetic material. Their experiments showed that DNA, not protein or RNA, was responsible for transformation in bacteria.
Question 14: Which radioactive isotopes did Hershey and Chase use in their experiments with bacteriophages?
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Correct Answer: B. ³²P and ³⁵S. ³²P labels DNA specifically (due to phosphate groups), while ³⁵S labels proteins (due to sulfur-containing amino acids).
Question 15: What is the key difference between DNA and RNA that makes DNA a better genetic material?
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Correct Answer: C. DNA is more chemically and structurally stable than RNA. The presence of deoxyribose sugar (lacking the 2′-OH group) makes DNA less reactive and less prone to degradation compared to RNA.
Question 16: Which of the following is NOT a reason why DNA is the predominant genetic material?
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Correct Answer: D. It can directly code for proteins. Genetic information in DNA is transcribed into RNA, which is then translated into proteins. RNA is more directly involved in protein synthesis.
Question 17: What is the transforming principle?
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Correct Answer: C. The genetic material that is transferred between bacteria. Griffith discovered the phenomenon, and Avery, MacLeod, and McCarty identified it as DNA.
Question 18: Why did Hershey and Chase use a blender in their experiment?
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Correct Answer: B. To separate the viral coats from the bacteria. Agitation in a blender detached the phage particles (protein coats) attached to the outside of the bacteria, allowing separation by centrifugation.
Question 19: Which of the following is NOT a property of a good genetic material?
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Correct Answer: B. High rate of mutation. A good genetic material requires stability and the ability to undergo slow mutations (evolution) but not a high rate, which would compromise genetic integrity.
Question 20: Why is RNA less suitable as a genetic material compared to DNA?
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Correct Answer: D. It is more reactive and easily degradable. The presence of the 2′-OH group in ribose makes RNA chemically less stable and more susceptible to hydrolysis than DNA.
Question 21: Why is RNA considered the first genetic material?
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Correct Answer: B. It can act as both a carrier of genetic information and a catalytic enzyme. This dual role (genetic storage and catalysis, like ribozymes) supports the RNA world hypothesis.
Question 22: What is the main advantage of DNA evolving from RNA as genetic material?
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Correct Answer: B. DNA is more stable and less prone to mutations. The chemical stability of DNA (double helix, deoxyribose sugar) makes it a better repository for genetic information.
Question 23: Which of the following is NOT a characteristic of the RNA world hypothesis?
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Correct Answer: D. Proteins were the first catalysts. The RNA world hypothesis proposes that RNA molecules (ribozymes) were the primary catalysts before the evolution of protein enzymes.
Question 24: What evidence suggests that RNA was the first genetic material?
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Correct Answer: C. RNA can act as both a carrier of genetic information and a catalyst. The discovery of ribozymes and RNA’s central role in protein synthesis (mRNA, tRNA, rRNA) support this hypothesis.
Question 25: Why did DNA eventually replace RNA as the primary genetic material?
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Correct Answer: B. DNA is more stable and less prone to degradation. DNA’s double-helical structure and deoxyribose sugar provide greater chemical stability, making it better suited for long-term storage of genetic blueprints.
Question 26: What did Watson and Crick propose regarding DNA replication?
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Correct Answer: B. Semiconservative replication. They suggested that the DNA double helix unwinds, and each strand serves as a template for the synthesis of a new complementary strand.
Question 27: Which researchers provided experimental proof for semiconservative DNA replication?
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Correct Answer: D. Meselson and Stahl. Their experiments using heavy (¹⁵N) and light (¹⁴N) nitrogen isotopes traced the distribution of parental DNA strands during replication in E. coli.
Question 28: What is the function of DNA polymerase?
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Correct Answer: B. To synthesize a new DNA strand from a template strand. DNA polymerase catalyzes the addition of deoxyribonucleotides to the 3′ end of a growing DNA chain, using the template strand as a guide.
Question 29: What is the role of DNA ligase in DNA replication?
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Correct Answer: C. To join DNA fragments together. DNA ligase forms phosphodiester bonds to seal the nicks between Okazaki fragments on the lagging strand and during DNA repair.
Question 30: What is the replication fork?
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Correct Answer: C. The Y-shaped region where DNA is unwound and replicated. It forms as the double helix separates, allowing access for replication machinery.
Question 31: Why is DNA replication discontinuous on one strand?
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Correct Answer: D. All of the above. DNA polymerase synthesizes only 5′ to 3′. Since strands are antiparallel, one strand (lagging strand) must be synthesized backwards relative to fork movement, in short Okazaki fragments.
Question 32: What are Okazaki fragments?
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Correct Answer: B. Short DNA fragments synthesized on the lagging strand. These are later joined together by DNA ligase to form a continuous strand.
Question 33: What is the origin of replication?
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Correct Answer: A. The point where DNA replication begins. It is a specific DNA sequence recognized by initiator proteins to start replication.
Question 34: In which phase of the cell cycle does DNA replication occur in eukaryotes?
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Correct Answer: B. S phase. The S phase (Synthesis phase) is dedicated to replicating the cell’s DNA before cell division.
Question 35: What is the result of a failure in cell division after DNA replication?
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Correct Answer: B. Polyploidy. If DNA replicates but the cell fails to divide (cytokinesis), the resulting cell will have multiple sets of chromosomes.
Question 36: What is the process of transcription?
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Correct Answer: B. The synthesis of RNA from a DNA template. Transcription is the process of copying genetic information from a DNA segment into an RNA molecule.
Question 37: Why is only one strand of DNA transcribed into RNA?
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Correct Answer: D. All of the above. Transcribing both strands would produce complementary RNAs, potentially forming double-stranded RNA, and would yield two different protein products from one gene if both were translated, which is generally not how genes function.
Question 38: What is a promoter?
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Correct Answer: A. A sequence of DNA that signals the start of a gene. The promoter is located upstream (towards the 5′ end) of the transcriptional start site and serves as the binding site for RNA polymerase.
Question 39: What is the difference between the template strand and the coding strand of DNA?
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Correct Answer: A. The template strand is transcribed into RNA, while the coding strand has the same sequence as the RNA (except for T instead of U). The RNA polymerase reads the template strand (also called antisense strand) to synthesize a complementary RNA molecule.
Question 40: What is a cistron?
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Correct Answer: A. A segment of DNA that codes for a polypeptide. It is essentially a gene, a functional unit that specifies the sequence of a single polypeptide chain.
Question 41: What is the difference between monocistronic and polycistronic genes?
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Correct Answer: A. Monocistronic genes code for a single polypeptide, while polycistronic genes code for multiple polypeptides. Monocistronic mRNAs are typical of eukaryotes, while polycistronic mRNAs (encoding multiple proteins from one transcript) are common in prokaryotes (e.g., operons).
Question 42: What are exons and introns?
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Correct Answer: A. Exons are coding sequences, while introns are non-coding sequences. In eukaryotic genes, introns are intervening sequences that are removed from the pre-mRNA during splicing, while exons are the sequences that are joined together to form the mature mRNA.
Question 43: What is the function of mRNA?
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Correct Answer: C. To carry genetic information from DNA to the ribosome. Messenger RNA (mRNA) contains the codons that specify the amino acid sequence for protein synthesis.
Question 44: What is the function of tRNA?
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Correct Answer: A. To carry amino acids to the ribosome. Transfer RNA (tRNA) acts as an adaptor molecule, matching specific amino acids to their corresponding codons on the mRNA during translation.
Question 45: What is the function of rRNA?
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Correct Answer: B. To catalyze protein synthesis. Ribosomal RNA (rRNA) is a major structural component of ribosomes and also possesses the catalytic activity (peptidyl transferase) responsible for peptide bond formation.
Question 46: Which enzyme catalyzes the process of transcription in bacteria?
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Correct Answer: B. RNA polymerase. Bacteria typically have a single type of RNA polymerase responsible for synthesizing mRNA, tRNA, and rRNA.
Question 47: What is the process of splicing?
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Correct Answer: B. The removal of introns and joining of exons in eukaryotic RNA. Splicing occurs in the nucleus and converts the primary transcript (pre-mRNA) into mature mRNA.
Question 48: What is the process of capping?
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Correct Answer: A. The addition of a methyl guanosine triphosphate to the 5′ end of eukaryotic RNA. The 5′ cap (a modified guanine nucleotide added in reverse linkage) protects the mRNA and is important for ribosome binding.
Question 49: What is the process of tailing?
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Correct Answer: B. The addition of a poly-A tail to the 3′ end of eukaryotic RNA. Polyadenylation (addition of a tail of adenine nucleotides) increases mRNA stability and aids in its export from the nucleus.
Question 50: Why can transcription and translation be coupled in bacteria?
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Correct Answer: D. All of the above. In prokaryotes (bacteria), there is no nuclear membrane separating transcription (DNA to RNA) and translation (RNA to protein). Translation can begin on the nascent mRNA molecule even before transcription is finished.
Question 51: How many nucleotides make up a codon?
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Correct Answer: C. 3. The genetic code is read in triplets of nucleotides, where each triplet (codon) specifies an amino acid or a stop signal.
Question 52: What is meant by the degeneracy of the genetic code?
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Correct Answer: B. Multiple codons can code for the same amino acid. There are 64 possible codons but only 20 common amino acids, so most amino acids are specified by more than one codon.
Question 53: Which of the following scientists was NOT involved in deciphering the genetic code?
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Correct Answer: D. Oswald Avery. Avery, MacLeod, and McCarty identified DNA as the transforming principle (genetic material). Gamow proposed the triplet nature, while Nirenberg and Khorana performed key experiments to determine codon assignments.
Question 54: What type of mutation causes sickle cell anemia?
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Correct Answer: A. A point mutation in the gene for beta globin chain. Specifically, a single nucleotide substitution (GAG to GTG) changes the codon for glutamic acid to a codon for valine at the sixth position.
Question 55: What is a frameshift mutation?
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Correct Answer: D. Both B and C. The insertion or deletion of a number of nucleotides not divisible by three shifts the triplet reading frame, altering all downstream codons and usually resulting in a nonfunctional protein.
Question 56: What is the function of tRNA?
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Correct Answer: C. To act as an adapter molecule between mRNA and amino acids. tRNA molecules read the mRNA codons via their anticodons and bring the corresponding amino acids to the ribosome.
Question 57: What is an anticodon?
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Correct Answer: B. A sequence of three nucleotides on tRNA that is complementary to a codon on mRNA. The anticodon loop of tRNA base-pairs with the mRNA codon during translation.
Question 58: Which of the following is NOT a feature of the genetic code?
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Correct Answer: C. It is ambiguous. The genetic code is unambiguous, meaning that a specific codon always codes for the same amino acid (with very few exceptions).
Question 59: What is the initiator codon?
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Correct Answer: D. AUG. AUG serves as the start codon, signaling the beginning of translation, and it also codes for the amino acid methionine (or formylmethionine in bacteria).
Question 60: What are the stop codons?
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Correct Answer: A. UAA, UAG, UGA. These three codons do not code for any amino acid and signal the termination of polypeptide synthesis.
Question 61: What is the process of translation?
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Correct Answer: C. The synthesis of protein from an RNA template. Translation decodes the nucleotide sequence of mRNA into the amino acid sequence of a polypeptide chain.
Question 62: What is the role of ribosomes in translation?
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Correct Answer: B. To catalyze protein synthesis. Ribosomes are the cellular machinery where mRNA is read, tRNAs deliver amino acids, and peptide bonds are formed.
Question 63: What is a translational unit in mRNA?
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Correct Answer: B. A sequence of mRNA that codes for a single polypeptide. It typically starts with a start codon (AUG), is followed by the codons specifying the polypeptide sequence, and ends with a stop codon (UAA, UAG, or UGA).
Question 64: What are UTRs?
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Correct Answer: A. Untranslated regions located at the 5′ and 3′ ends of mRNA. The 5′ UTR is upstream of the start codon, and the 3′ UTR is downstream of the stop codon. They contain regulatory elements.
Question 65: What is the correct order of events in translation?
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Correct Answer: D. Initiation, elongation, termination. Initiation involves ribosome assembly on mRNA, elongation is the stepwise addition of amino acids, and termination occurs when a stop codon is reached.
Question 66: At what levels can gene expression be regulated in eukaryotes?
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Correct Answer: D. All of the above. Eukaryotic gene expression is complex and can be controlled at multiple steps, including transcription initiation, RNA processing, mRNA transport, translation, and protein modification/stability.
Question 67: What is an operon?
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Correct Answer: B. A unit of gene expression found in prokaryotes. An operon is a cluster of genes under the control of a single promoter and operator, allowing coordinated regulation.
Question 68: What is the function of an operator in an operon?
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Correct Answer: C. To regulate the access of RNA polymerase to the promoter. The operator is a DNA sequence, typically located near or overlapping the promoter, where a repressor protein can bind to block transcription.
Question 69: What is the lac operon?
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Correct Answer: A. An operon that regulates lactose metabolism in E. coli. It includes genes encoding proteins needed to transport and break down lactose.
Question 70: What is the function of the lacZ gene in the lac operon?
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Correct Answer: A. To code for beta-galactosidase. This enzyme hydrolyzes lactose into glucose and galactose.
Question 71: What is the function of the lacY gene in the lac operon?
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Correct Answer: B. To code for permease. This membrane protein transports lactose into the bacterial cell.
Question 72: What is the function of the lacA gene in the lac operon?
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Correct Answer: C. To code for transacetylase. This enzyme acetylates galactosides, though its precise role in lactose metabolism is less critical than the other two enzymes.
Question 73: What is the role of lactose in the lac operon?
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Correct Answer: B. It acts as an inducer. Specifically, allolactose (an isomer of lactose) binds to the lac repressor protein, changing its shape so it can no longer bind to the operator, thus allowing transcription.
Question 74: How is the lac operon regulated?
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Correct Answer: C. By both positive and negative regulation. It is under negative control by the lac repressor (repressed unless lactose is present) and positive control by CAP-cAMP (activated when glucose is low).
Question 75: What happens to the lac operon when glucose is present?
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Correct Answer: B. It is repressed. High glucose levels lead to low cAMP levels. Without sufficient cAMP, the activator protein (CAP) cannot bind effectively, leading to low levels of lac operon transcription even if lactose is present (this is called catabolite repression).
Question 76: What was the main goal of the Human Genome Project?
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Correct Answer: D. All of the above. The HGP was an international effort to sequence the entire human genome, identify the genes, and make the data accessible for research.
Question 77: What is the estimated size of the human genome?
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Correct Answer: C. 3 billion base pairs. The haploid human genome consists of approximately 3.3 billion base pairs.
Question 78: What is the approximate number of genes in the human genome?
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Correct Answer: B. 30,000. Initial estimates were higher, but the HGP revealed fewer protein-coding genes than expected, currently estimated around 20,000-25,000, though the total including non-coding RNA genes is higher (~30,000 is a reasonable approximation given in many texts).
Question 79: What percentage of nucleotide bases are the same in all people?
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Correct Answer: D. 99.9%. Despite individual differences, the vast majority of the DNA sequence is identical between any two humans.
Question 80: What are ESTs?
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Correct Answer: A. Expressed Sequence Tags. ESTs are short subsequences of cDNA sequences, representing portions of transcribed genes (mRNA).
Question 81: What is sequence annotation?
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Correct Answer: B. Sequencing the whole set of the genome and later assigning different regions in the sequence with functions. Annotation involves identifying genes, regulatory elements, and other features within the raw DNA sequence data.
Question 82: Which of the following was NOT a commonly used host for cloning DNA fragments during the Human Genome Project?
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Correct Answer: C. Fruit fly & D. Nematode. Bacteria (E. coli) and Yeast (S. cerevisiae) were the primary hosts for cloning large DNA fragments into BACs and YACs, respectively, which were essential tools for sequencing.
Question 83: Who developed the method used for sequencing DNA fragments in the Human Genome Project?
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Correct Answer: C. Frederick Sanger. The dideoxy chain termination method, developed by Sanger, was the dominant sequencing technology used throughout the HGP.
Question 84: What are SNPs?
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Correct Answer: A. Single Nucleotide Polymorphisms. SNPs are the most common type of genetic variation among people, representing differences at a single nucleotide site in the DNA sequence.
Question 85: What is the significance of repetitive sequences in the human genome?
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Correct Answer: C. They provide information about chromosome structure, dynamics, and evolution. While some repetitive elements can influence gene expression, their primary known roles relate to chromosome structure (e.g., centromeres, telomeres) and genome evolution. They do not code for proteins.
Question 86: Which human chromosome has the most genes?
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Correct Answer: A. Chromosome 1. Being the largest chromosome, Chromosome 1 contains the highest number of genes.
Question 87: Which human chromosome has the fewest genes?
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Correct Answer: D. Chromosome Y. The Y chromosome is significantly smaller than the X chromosome and contains the fewest genes, mostly related to male sex determination and fertility.
Question 88: What is one of the applications of SNPs?
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Correct Answer: A. Identifying disease-associated sequences. SNPs located near disease genes can serve as genetic markers in genome-wide association studies (GWAS) to help find genes linked to diseases or traits.
Question 89: What is bioinformatics?
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Correct Answer: B. The use of high-speed computational devices for data storage and retrieval, and analysis of biological data. Bioinformatics applies tools from computer science and statistics to manage and analyze large biological datasets, like genomic sequences.
Question 90: What is a potential application of the Human Genome Project in biological research?
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Correct Answer: D. All of the above. The HGP laid the foundation for large-scale biological studies, enabling research across genomics, transcriptomics, proteomics, and systems biology.
Question 91: What is DNA fingerprinting?
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Correct Answer: B. A technique to identify variations in individuals of a population at the DNA level. It compares specific, highly variable regions of DNA (like repetitive sequences) between individuals.
Question 92: What type of DNA sequences is used in DNA fingerprinting?
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Correct Answer: C. Repetitive DNA. DNA fingerprinting primarily relies on polymorphisms (variations) found within repetitive DNA regions, such as microsatellites (STRs) and minisatellites (VNTRs), which are mostly non-coding.
Question 93: What is satellite DNA?
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Correct Answer: A. DNA that forms a minor peak during density gradient centrifugation. Satellite DNA consists of highly repetitive sequences and often has a different base composition from the bulk genomic DNA, causing it to separate as distinct bands (‘satellites’) during centrifugation.
Question 94: What is polymorphism?
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Correct Answer: A. The presence of two or more alleles of a gene or DNA sequence in a population. DNA polymorphism refers to variations in DNA sequences among individuals, which form the basis for DNA fingerprinting.
Question 95: Which of the following is NOT a step involved in DNA fingerprinting?
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Correct Answer: C. Sequencing the entire DNA. DNA fingerprinting analyzes specific variable regions, not the entire genome sequence.
Question 96: What are VNTRs?
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Correct Answer: B. Variable Number Tandem Repeats. VNTRs are regions in the genome where a short sequence of nucleotides is organized as a tandem repeat, and the number of repeats varies among individuals.
Question 97: What technique can be used to increase the sensitivity of DNA fingerprinting?
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Correct Answer: A. Polymerase Chain Reaction (PCR). PCR allows amplification of the specific DNA regions (like STRs) used for fingerprinting, enabling analysis from very small samples.
Question 98: Which of the following is NOT an application of DNA fingerprinting?
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Correct Answer: C. Determining the sequence of a gene. DNA fingerprinting compares the lengths or patterns of variable regions, it doesn’t determine the exact base-by-base sequence of a specific gene.
Question 99: Who developed the technique of DNA fingerprinting?
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Correct Answer: C. Alec Jeffreys. Sir Alec Jeffreys developed the first DNA profiling techniques using VNTRs in 1984.
Question 100: What is the basis of DNA fingerprinting?
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Correct Answer: A. The presence of repetitive sequences in DNA showing high degree of polymorphism. Variations (polymorphisms) in the number of repeats within these sequences (like VNTRs and STRs) create unique patterns for individuals.