-20 or -80, DNA is stable molecule so won't go that bad. If you want to use multiple time then you can store with aliquet to avoid freez thaw.

As Dhirij recommended, DNA is more stable than RNA. So, You can Store it in -20 or -80 Refrigerator for long time.

you can re suspend the DNA pellet in TE buffer or Filter sterilize autoclaved milli Q.then store it on -20 degree..don't store it on -80 degree..i have experienced the shearing of DNA when stored in -80 degree, so its safe to store in -20 for long term storage..and make aliquot of your DNA sample so you don't need to freeze thaw it every time..

One thing to avoid: acidic solutions. That includes some extra-pure H2O. We have destroyed quite a number of PCR primers that way, after storing aqueous solutions for 1-2 years at -20°C. In TE buffer they keep much better.

Although DNA is quite stable but it can degrade in certain condition. so avoid those conditions

1. DNAse contamination : use autoclave miliq water for TE buffer.

2. frequently Freeze thaw: make the aliquot or store @ 4 degree C.

3.Avoid Water for storage: use TE buffer pH 7.4. (avoid high salt strength during pH maintenance of buffer.)

For very long time storage use -80 freezer.

The standard combination of TrisHCl (10mM pH8.0) and EDTA (1mM) works well. The basic conditions reduce rate of depurination while chelation discourages nuclease activity (most are dependent on divalent cations). We noticed a significant improvement in the stability of working multiplex PCR primer stocks prepared in TE (10:1, pH8) compared with dulicate primers reconstituted in molecular biology grade water by same vendor. For longterm stability, primers or DNAs may also be stored in the freezer as lyophilized pellets.

As a general rule isolated DNA can be stored at 4oC for several weeks, at -20oC for several months and at -80oC for several years.

• short-term storage (weeks) 4 degree centigrade in Tris-EDTA
• Medium-term storage (months) -80 degree centigrade in Tris-EDTA
• Long-term storage (years) -80 degree centigrade as a precipitate in ethanol
• Long-terms storage (decades) -164 degree centigrade or dried.

can DNA be stored in same deep freezer where plasma aliquots are being stored?