A mixture of fragmented DNA was electrophoresed in agarose gel. After

1.	A mixture of fragmented DNA was electrophoresed in agarose gel. After staining the gel with ethidium bromide, no DNA bands were observed. What could be the reason?
Answer» The reasons that could be possible are as follows: i. DNA sample that was loaded on the gel may have got contaminated with nuclease (exo- or endo- or both) and completely degraded. ii. Electrodes were put in opposite orientation in the gel assembly, *i.e.,* anode 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. iv. After staining with Ethidium bromide it was not observed under UV

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

Answer»

The reasons that could be possible are as follows:

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

ii. Electrodes were put in opposite orientation in the gel assembly, i.e., anode 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.

iv. After staining with Ethidium bromide it was not observed under UV

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