southern blotting problem

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hi i am rao,working in plant transformation.i am faceing problem in southern blotting,restriction was good,DNA was transferred to nylom membrane nothing was able to see in the gel.after hybrdization followed by development, i am not getting any signals.i tried many times,nothing was comeing, only positive is giveing signal.what could be the problem?please give me some suggestions

thanq
rao

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