Biology

DNA and Genetics

1,095 Questions

DNA and genetics questions explore molecular biology, DNA replication, and genetic engineering techniques. These topics are essential for various competitive exams requiring a strong foundation in life sciences. Practice these questions to understand complex biological processes thoroughly.

DNA replication mechanismsGenetic engineering techniquesGene editing toolsPolymerase chain reactionDNA sequencing methods

DNA and Genetics Questions

Multiple choice

Which of the following cannot be used as a vector?

  1. Bacteriophage

  2. Plasmid

  3. Bacterium

  4. YAC

  5. Retrovirus
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Bacteria are used as host cells, not as vectors. They are large in size and contain a single circular chromosome. However, it provides an ideal environment for cloning of rDNA irrespective of vectors which may be a bacteriophage, plasmid, YAC or BAC.

Multiple choice

Restriction enzymes cut at which of the following types of sites?

  1. Palindrome

  2. Ori

  3. Primer

  4. Promoter

  5. Okazaki fragments
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A palindrome is a region on a double stranded DNA where the 5' to 3' sequence on one strand matches the 5' to 3' on the complementary strand. Such sites are cleaving sites for specific restriction enzymes.

Multiple choice

In the Blue-White screening method, lacZ gene is inserted in the vector. It codes for the enzyme beta-galactosidase, which breaks a colourless substance X-gal to an insoluble blue product. The lacZ gene also contains restriction sites. In this screening method, what does a blue colony indicate?

  1. Colony of host cells having non-recombined vector

  2. Colony of host cells having recombined vector

  3. Colony of host cells producing the target gene product

  4. Colony of host cells not producing beta-galactosidase

  5. Colony of host cells containing a probe
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The lacZ gene containing restriction sites is used as a marker gene. The target DNA is inserted in between this gene. In a recombined vector, insertion inactivates lacZ gene, so the enzyme beta galactosidase will not be produced and hence, X-gal will not be converted to the blue insoluble product. So, a blue colony indicates that insertion has not taken place and hence, the enzyme beta galactosidase is produced. It indicates the presence of non-recombined vector.

Multiple choice

A researcher creates an artificial vector. It has an ori region containing the sequence GAATTC. It also has a lacZ marker gene containing the sequence HindIII enzyme. Apart from these, there are restriction sites for EcoRII, BamHI and TaqI away from the marker gene. Now, he wants to cut out a target gene, which has restriction sites for the following restriction endonucleases. Which restriction enzyme should he use?

  1. EcoRI

  2. BamHI

  3. HindIII

  4. TaqI

  5. EcoRII
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

It’s the most appropriate choice. Its restriction site is present inside a marker gene and hence, the researcher will be able to screen for recombinants later.

Multiple choice

E.coli bacteria are placed in a medium, which is inoculated with radioactive guanosine for 5 minutes. Then it was made to replicate in a normal medium. Which of the following is correct for the replication process of DNA?

  1. Each strand will be partly radioactive.

  2. Both the strands of DNA are radioactive.

  3. Only one strand will be radioactive.

  4. Radioactivity is seen only on the leading strand.

  5. None of the strands is radioactive.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Only one strand will be radioactive. Replication of DNA is semi-conservative in nature. Hence, a new strand is formed on the template DNA strand. The new strand while replicating use radioactive guanosine from the medium but the template strand would not have the radioactive G. Therefore after 5 minutes, only one strand, i.e. the newly produced strand will have the radioactive guanosine.

Multiple choice

With which of the following does the operator gene in an operon of a prokaryote (E. coli) combine?

  1. Repressor protein (to switch on gene action)

  2. Inducer gene (to switch off structural gene action)

  3. Inducer gene (to switch on structural gene action)

  4. Promoter gene (to start transcription of structural gene)

  5. Regulator or repressor protein (to switch off structural gene action)
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Regulator or repressor protein (to switch off structural gene action): In Lac operon as it is described by Jacob and Monad in E.coli, the operator gene combines with repressor tetramer produced on translation of mRNA transcripted from inducer or regulatory gene. It inhibits the RNA polymerase from running over the structural genes. This consequently switches off the functioning of the structural genes.

Multiple choice

Proof reading and DNA repair are the characteristic functions of DNA polymerase I in prokaryotic replication. Identify the enzyme having the same function in eukaryotes.

In eukaryotic replication,  5 different kinds of polymerases have been demonstrated. They perform different functions.

  1. DNA polymerase α

  2. DNA polymerase β and DNA polymerase γ

  3. DNA polymerase γ

  4. DNA polymerase δ, DNA polymerase β and DNA polymerase ε

  5. DNA polymerase ε
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

DNA polymerase β is involved in the repair of DNA, and proof reading is done by DNA polymerase δ. DNA polymerase ε is involved in DNA synthesis on the lagging strand and the proof reading function.

Multiple choice

Match the following: Column A Column B P. PCNA i. Single strand binding protein Q. RPA ii. Prevent continuous DNA loss at the end of Chromosome R. Telomeres iii. Fragmented DNA produced on the lagging strand S. Okazaki fragments iv. Leading strand synthesis

  1. P - ii, Q - i, R - iii, S - iv

  2. P - iii, Q - i, R - iv, S - ii

  3. P - iv, Q - i, R - ii, S - iii

  4. P - ii, Q - iv, R - iii, S - i

  5. P - iii, Q - iv, R - i, S - ii
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Proliferating cell nuclear antigen (PCNA) along with DNA polymerase δ helps in leading strand synthesis. Replication protein A (RPA) is a single strand binding protein. Telomeres are the special structures that prevent continuous DNA loss at the end of chromosome. The fragmented DNA produced during the lagging strand synthesis is Okazaki fragment.

Multiple choice

If a sudden mutation occurs to the gene responsible for coding DNA polymerase α in a unicellular organism, which function will be stopped in that cell?

In eukaryotic replication,  5 different kinds of polymerases have been demonstrated. They perform different functions.

  1. Initiation of leading strand synthesis

  2. Initiation of replication in both leading and lagging strands

  3. Mitochondrial replication

  4. DNA proof reading in lagging strand

  5. Lagging strand synthesis
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Initiation of replication in both leading and lagging strands. As DNA polymerase α is responsible for synthesis of RNA primer on both the strands, initiation of replication is stopped in both leading and lagging strands. RNA primer provides free –OH at the 3’ end for the attachment of deoxyribonucleotides on both the strands and if it is unable to form, then replication will be stopped.

Multiple choice

Match the following: Column A Column B P. Repressor protein i. Fine structure of gene of R II locus in T4 phage Q. Puromycin ii. Produced from inducer R. eEF1βγ iii. Premature termination of polypeptide S. Benzer iv. Eukaryotic translation

  1. P - ii, Q - iv, R - i, S - iii

  2. P - iv, Q - ii, R - i, S - iii

  3. P - iv, Q - iii, R - ii, S - i

  4. P - iii, Q - iv, R - ii, S - i

  5. P - ii, Q - iii, R - iv, S - i
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

In operon system, repressor protein is produced from inducer gene. Puromycin produced from Streptomyces alboniger responsible for premature termination of polypeptide.  eEF1βγ is the elongation factor in eukaryotic translation. Seymour Benzer discovered fine structure of gene of R II locus in T4 phage.

Multiple choice

Transduction method of genetic recombination in Salmonella typhimurium was first demonstrated by

  1. Zinder and Lederberg

  2. Griffith

  3. Lederberg and Tautum

  4. A. V. Leeuwenhoek

  5. R. Koch
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Transduction method of genetic recombination in bacteria, e.g. Salmonella typhimurium was first demonstrated by Zinder and Lederberg in 1952. It is the transfer of genes (small double stranded piece of DNA) from one bacterial cell to another via virus (bacteriophage).

Multiple choice

Meselson and Stahl proved that DNA replication is semiconservative. E.coli bacteria was grown in N15-NH4Cl medium, then washed and incubated with N14 compounds for 3 generations. Then CsCl density gradient centrifugation of isolated DNA showed semiconservative DNA replication. What is the pattern of band formation, if formed in the following way: N14, N14/15, N15?

  1. Thin band at N14, thick band at N15

  2. Thin bands at N15 and N14/15

  3. Thick band at N14 and thin band at N15

  4. Thick band at N14/15 and thin band at N15

  5. Thick band at N14
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Since, the Bacteria has been transferred from N15 to N14 medium, the source of nitrogen for synthesis of DNA will be non radioactive. Now, the bacteria was grown in N15 medium after which it was grown for several generations in N14 medium. So, after centrifugation thick band will be formed in N14 zone and a thin band will be formed in the N15 zone as initially the DNA contained N15 nitrogen.

Multiple choice

Deletion of the leader sequence of trp operon of E.coli causes _________.

There is a leader sequence in gene controlling synthesis of tryptophan.

  1. increased transcription of trp operon

  2. decreased transcription of trp operon

  3. decreased transcription of trp operon in presence of tryptophan

  4. no effect on transcription

  5. transcription to occur constitutively
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Attenuator produces terminator loop in presence of high tryptophan and anti terminator loop in presence of low tryptophan. The attenuator sequence is present within the leader sequence of the operon. In absence of leader sequence, there will be no attenuation. So, no attenuator loop will be formed and transcription of operon will increase.