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

Question : A. mixture electrophoresed in an agarose gel. After stainin

1.	Question : A. mixture electrophoresed in an agarose gel. After staining of fragmented DNA was the gel with ethidium bromide, no DNA bands were observed. What could be the reason ?
Answer» Solution :The reasons 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 that is 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.