Question

The cutting of DNA at specific locations became possible with the discovery of

• A. Ligases
• B. Restriction enzymes
• C. Probes
• D. Selectable markers

Answer 1

The correct option is B Restriction enzymes

Probes
A probe is a single-stranded sequence of DNA or RNA that is labeled with the radioactive substance and used to find its complementary sequence.

Selectable markers
Selectable marker is a gene in a vector that helps in the selection of transformants (host cells which have successfully taken up the foreign DNA) and non-transformants (cells which have not taken up the vector DNA).

For example, antibiotic resistance genes in the vector act as selectable markers because they confer antibiotic resistance to the transformants while the non-transformants remain susceptible to antibiotics
.
Ligases
Enzyme ligase is used to join two DNA fragments by the formation of phosphodiester bonds.

For example, Ligase enzyme joins the DNA of interest with the vector DNA, thus helping in the formation of recombinant DNA in genetic engineering.

Restriction enzymes
Restriction endonucleases are the enzymes which cleave the DNA by digesting phosphodiester bonds at the specific sequences within the DNA. Examples include EcoR I.

This helps in cutting the vector and the DNA of interest, so that the DNA of interest can be inserted into the vector. The two DNA molecules are then ligated to form rDNA in genetic engineering. Genetic engineering is made possible by the discovery of the restriction endonucleases in the purified form that can cut the DNA at a specific location.

Final answer
(D) Restriction enzymes