Name: Genetic Engineering in Health
Uploaded: 2019-07-19
Duration: 5 min 10 s
Description: Genetic Engineering holds the key to the door of wide possibilities. Watch this video to learn how genes are being edited and stitched and how they impact humanity and life!

Question

A mixture of fragmented DNA was electrophoresed in an agarose gel. After staining the gel with ethidium bromide, no DNA bands were observed. What could be the reason?

Accepted Answer

The gel electrophoresis is a technique to separate the DNA segments based on their size and charge. This procedure involves different steps. Any error in one of these steps may lead to the absence of the appearance of DNA bands after autoradiography. These steps are as follows:

(i) The DNA fragments obtained after cutting with the endonuclease enzymes are placed in the agar gel. During this step, if exonuclease enzymes are added these will cut the DNA from the terminal ends and ultimately destroying it.

(ii) In the next step, the electric field is applied so that the negatively charged DNA fragments (the charge is due to the phosphate group) move to the positively charged electrode. If these electrodes are placed in opposite orientation in the gel assembly, the DNA will not be collected in the wells created in agarose gel.

(iii) Since the DNA segments are not visible in the white light, a compound called ethidium bromide is used to stain the DNA segments which on exposure to UV light is seen as orange-red bands. If a proper quantity of stain is not added it may result in non-staining of DNA and these will not be seen. If UV light is not used, the DNA fragments will not be visible.

A mixture of fragmented DNA was electrophoresed in an agarose gel. After staining the gel with ethidium bromide, no DNA bands were observed. What could be the reason?

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