Question

A gene of interest (GOI), amplified using PCR, can be isolated using agarose gel electrophoresis by ____i____ and the DNA is extracted out. This process is known as ____ii____.

• A. i - cutting the gel of the desired band, ii - amplification of DNA
• B. i - scraping the gel of the desired band, ii - extraction of DNA
• C. i - cutting the portion of gel of the desired band, ii - elution of DNA
• D. i - extracting the DNA from the entire gel, ii - digestion of DNA with restriction enzymes

Answer 1

The correct option is C i - cutting the portion of gel of the desired band, ii - elution of DNA

Agarose gel electrophoresis is a technique that is used to separate the DNA molecules of varying sizes under the influence of an electric field. The DNA molecules migrate to different distances towards the positive terminal (anode) in the agarose gel matrix based on their sizes.

Comparing the position of the particular DNA fragment with the ladder (a solution of DNA of different lengths used as a reference to predict the size of unknown DNA molecules), the approximate molecular weight of the DNA molecule/ fragments can be determined. This will help in the identification of the gene of interest.


Let the theoretical expected base pairs in our gene of interest be around 300bp. On separating the mixture of DNA fragments, the band that corresponds to the band of the ladder with 300bp is our gene of interest.

The gene of interest is isolated from the agarose gel by elution. Small slice of gel containing the desired band (desired gene of interest) is excised from the entire gel block. The gel slice with the desired DNA fragment is then treated with solvents and buffers and filtered. This helps in the extraction of the purified DNA fragment containing the gene of interest. This process is known as the elution of DNA.