question_answer

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

Answer:

After staining the agarose gel with ethidium bromide, no DNA bands were observed during electrophoresis, it could be due to the following reasons

(i) DNA sample that was loaded on the gel may have got contaminated with nuclease (exo or endo both) so that it got completely degraded.

(ii) Electrodes were put in such an orientation in the gel assembly that anode is towards the wells (where DNA sample is loaded). Since, DNA molecules are negatively charged they move towards anode and hence, move out of the gel instead of moving into the matrix of gel.

(iii) Ethidium bromide was not added at all or was not added in sufficient concentration and so, DNA was not visible.