what solution helps the dna to come out of solution or to precipitate
Ethanol precipitation DNA is precipitated by first ensuring that the correct concentration of positive ions is present in solution (too much will result in a lot of salt co-precipitating with DNA, too little will result in incomplete DNA recovery) and then adding two to three volumes of at least 95% ethanol. Many protocols advise storing DNA at low temperature at this point, but there are also observation that it does not improve DNA recovery, and may even lower precipitation efficiency while using over-night incubation time.[2][3] In most cases, good efficiency is achieved at room temperature but when possible degradation is taken into account it is probably best to incubate DNA on wet ice. Optimal incubation time depends on the length and concentration of DNA. Smaller fragments and lower concentrations will require longer times to achieve acceptable recovery. For very small lengths and low concentrations over-night incubation is recommended. In such cases use of carriers like tRNA, glycogen or linear polyacrylamide can greatly improve recovery.