Hi there,

Isopropanol precipitated DNA is not always visible (depending on the amount). So if the amount is actually low what you have to make sure of is to precipitate DNA long enough (if the amount of DNA is low go for longer incubation in the cold) and to spin the samples long enough to pellet DNA efficiently (at least 20 minutes, 10 000g, 4°C) , to spot the side of the tube where you expect the DNA pellet and discard the supernatant on the opposite side to avoid resuspension. Don't hesitate in spinning samples again when washing the pellets with 70% ethanol.

Thank u so much for your valuable  answer sir..i will try this..Hope for a good result..

Hey, additional to Dominique Liger, i store my samples overnight at 4°C in isopropanol and go on further with the protocol the next day. Maybe this could also be helpful. Good luck!