Genetic Engineering

The origin of replication lets the vector copy itself in the host cell. It is an essential feature for gene cloning.

For cloning, plasmid copies must be made. Without replication, the number of gene copies will not increase.

Putting a human gene into bacteria to make a product is an application of recombinant DNA technology. Insulin production is a good example.

Restriction enzyme cuts DNA and DNA ligase joins it. This is a basic pair in genetic engineering.

Restriction enzyme cuts DNA, but ligase is required for joining. Remember both cutting and joining steps.

DNA fragments carry a negative electrical charge, so all of them move toward the positive electrode in an electric field. The porous gel matrix hinders larger fragments more strongly, whereas smaller fragments pass through its pores more easily and travel farther. Therefore, option B is incorrect because both small and large DNA fragments are charged. Exam tip: Under the same conditions, the DNA band that travels farther is generally the smaller fragment.

A good plasmid vector may have an origin of replication and selectable marker. That makes it useful in gene cloning.

In agricultural biotechnology, useful traits and safety testing are both important. Responsible use is an important exam point.

First the desired gene is selected, then joined with a vector and inserted into a host. This simple order helps in exams.

The target gene carries information for the desired trait. In exams, consider gene isolation as an early step.

The direct answer is A: joining DNA with a vector is done to deliver the DNA into a host cell. A vector is a carrier molecule, commonly a plasmid, that can enter or be maintained in a suitable host and often contains an origin of replication and selectable marker. Step by step: the desired gene is prepared; it is joined to the vector using compatible ends and DNA ligase; the recombinant vector is introduced into a host cell; the host can copy the vector and sometimes express the gene. Option A is correct because delivery and maintenance of foreign DNA are the central purposes of a vector. Option B is wrong because DNA is not changed into water. Option C is wrong because destroying DNA defeats the aim of genetic engineering. Option D is wrong because DNA does not become a stone; the vector is a functional biological carrier. Memory cue: vector means vehicle—it carries the gene to the host.

Bacteria divide quickly, so gene copies can increase fast. That is why they are common hosts in cloning.

The correct answer is A: DNA is identified on the basis of its base sequence. DNA is built from four bases—A, T, G, and C—and the order of these bases stores genetic information. A gene is recognised or selected by comparing its sequence with a known sequence, using complementary base pairing or other molecular detection methods. Thus, the sequence, not a superficial physical feature, provides the meaningful identity. Option A is correct because sequence determines the information and helps distinguish one gene or DNA region from another. Option B is wrong because cell colour is not the genetic code and cannot reliably identify a DNA sequence. Option C is wrong because the smell of water has no role in molecular DNA identification. Option D is wrong because soil hardness is unrelated to the bases in DNA. Memory cue: DNA information is written in the order of bases, like letters arranged into a message.

Restriction enzymes cut DNA at special recognition sites. That is why they are called molecular scissors.

DNA ligase forms bonds between DNA fragments and joins them. Remember it as the joining enzyme in gene cloning.

After foreign DNA is inserted, the plasmid is called a recombinant plasmid. It can be introduced into a host.

Controlled modification helps achieve the desired result. Uncontrolled changes can increase risks.

The correct answer is A: transformation. In genetic engineering, transformation means that a host cell takes up foreign or recombinant DNA from outside the cell. The introduced DNA may then remain in the cell, be copied, or express a gene if the necessary conditions are present. In laboratory work, cells may be made competent so that DNA can enter by a suitable method. Option A is correct because it names the process of introducing external DNA into a host cell. Option B, evaporation, is the change of a liquid into vapour and has no role in DNA uptake. Option C, sedimentation, is the settling of particles under gravity and does not describe genetic entry. Option D, contraction, means becoming smaller or tightening and is not the term for foreign-DNA uptake. Memory cue: transformation means a cell takes in new genetic information and may acquire a new trait.

Cells with an antibiotic resistance gene survive in such medium. This makes selection of correct cells easier.

Plasmids are small DNA molecules that can be used as vectors in cloning. That is why they are isolated.

Gel electrophoresis separates DNA fragments using an electric field. DNA moves toward the positive electrode due to its negative charge.

Visible bands in a gel show the positions of DNA fragments. They are interpreted based on size.

During denaturation, high temperature separates the two hydrogen-bonded DNA strands. In the subsequent annealing step, primers bind to the single-stranded DNA, and extension synthesizes the new DNA strand. Exam tip: remember the PCR sequence as denaturation, annealing, and extension.

During PCR extension, DNA polymerase adds nucleotides from the primer’s 3′ end to synthesize a new DNA strand complementary to the template. Strand separation occurs during denaturation, primer binding occurs during annealing, and cutting at specific sites is performed by restriction enzymes. Exam tip: The extension step is commonly carried out at about 72°C, suitable for Taq DNA polymerase.

DNA polymerase adds complementary nucleotides to a template strand to synthesise a new DNA strand. Therefore, it is essential in DNA replication and PCR. Cutting DNA into smaller fragments is performed by nuclease or restriction enzymes, not by DNA polymerase. Exam tip: remember that ‘polymerase’ builds a polymer by joining nucleotides.