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

Recombinant DNA (or rDNA) is made by combining DNA from two or more sources. The yeast most commonly used for protein expression using recombinant DNA techniques in different organisms is

  1. Fleischmann's yeast

  2. Pichia stipitis

  3. Pichia pastoris

  4. Pichia methanolica

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

Pichia pastoris is a species of methylotrophic yeast. Pichia is widely used for protein expression using recombinant DNA techniques. Hence, it is used in biochemical and genetic research in academia and the biotechnical industry.

Multiple choice

Which of the following genes is expressed at a constant rate, without being subjected to regulation?

  1. Gratuitous inducer gene

  2. Repressor gene

  3. Constitutive gene

  4. Oncogene

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

Constitutive genes are expressed continuously at a constant rate without regulation - they're 'housekeeping' genes essential for basic cellular functions like metabolism, structure, and maintenance. Unlike regulated genes that respond to environmental signals, constitutive genes maintain baseline expression levels. Gratuitous inducer genes, repressor genes, and oncogenes are all subject to regulation.

Multiple choice

The step that initiates the process of 'Southern Blot Technique' is

  1. fragmentation of DNA by restriction of endonucleases

  2. electrophoresis of cut pieces on agarose gel

  3. isolation of DNA from suspected cell

  4. denaturation of DNA by treating it with NaOH

  5. transfer to a membrane

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Southern blot begins with DNA isolation from cells - you cannot fragment, separate, or transfer DNA that hasn't been extracted first. After isolation (C), the DNA is cut with restriction enzymes (A), separated by electrophoresis (B), denatured (D), and transferred to a membrane (E). Option C is logically first - you need the DNA material before any processing.

Multiple choice

Which of the following processes is carried out during the preparation of chimeric DNA?

  1. Specific gene is isolated and amplified.

  2. Plasmids are replicated independently from bacterial DNA.

  3. Restriction endonuclease and human DNA are incubated together for annealing.

  4. Gene of interest & plasmid are cut with two different restriction enzymes.

  5. Restriction enzymes help in joining two DNA molecules.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Creating chimeric DNA (recombinant DNA) begins with isolating and amplifying the specific gene of interest - you need sufficient copies of the target gene before combining it with a vector. Options B, D, and E describe other steps in recombinant DNA technology, while C incorrectly describes annealing without specifying the correct components.

Multiple choice

In the function of the lac operon in E. coli, the lac genes are transcribed in the presence of lactose because

  1. RNA polymerase binds to the operator

  2. the repressor binds to the promoter

  3. an isomer of lactose binds to the repressor

  4. CAP does not bind to the operator

  5. of the absence of cAMP
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When lactose is present, some of it is converted to allolactose, which binds to the lac repressor protein. This binding causes the repressor to change shape and release from the operator site, allowing RNA polymerase to transcribe the lac genes. CAP (catabolite activator protein) actually binds to the promoter, not the operator.

Multiple choice

When tryptophan is present in the environment of E. coli, the tryptophan binds to the

  1. trp operon

  2. trp promoter

  3. trp operator

  4. trp repressor

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

When tryptophan is abundant in the environment, it acts as a corepressor by binding to the trp repressor protein. This binding changes the repressor's conformation, allowing it to bind to the trp operator and block transcription of the tryptophan biosynthesis genes. This is negative feedback regulation.

Multiple choice

Which of the following vectors has the highest DNA insert capacity?

  1. Plasmids

  2. Phages

  3. Cosmids

  4. Yeast artificial chromosomes

  5. Bacterial artificial chromosomes
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Yeast artificial chromosomes (YACs) can accommodate the largest DNA inserts, ranging from hundreds of kilobases to over 2 megabases. This far exceeds the capacity of BACs (100-200 kb), cosmids (35-45 kb), phages (5-25 kb), or plasmids (typically <15 kb). YACs are essential for cloning large genomic fragments.

Multiple choice

Restriction enzymes that produce staggered cuts known as “sticky ends” are useful because

  1. sticky ends stick to almost anything

  2. sticky ends allow fragment ends to reanneal, which is usually desirable

  3. DNA fragments, cut with the same enzyme, can anneal to each other

  4. staggered cuts won't join with other DNA fragments regardless of how they were cut

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Sticky ends are complementary single-stranded overhangs created when restriction enzymes make staggered cuts. When DNA fragments are cut with the same enzyme, they produce identical sticky ends that can anneal through base pairing. This allows DNA ligase to join the fragments covalently, forming recombinant DNA molecules.

Multiple choice

Various retro viruses incorporates their genetic material into host chromosomes. Which of the following is used by viruses to insert their genetic material into the host genomes?

  1. Inverted repeat

  2. Direct repeats

  3. Long terminal repeats

  4. Tandem repeats

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

Long terminal repeats are identical sequences of DNA that repeat hundreds or thousands of times found at either end of retrotransposons or proviral DNA formed by reverse transcription of retroviral RNA. They are used by retro viruses to insert their genetic material into the host genomes.