Hello:

I'm new in the forum. I hope someone could help me. I have a couple of samples of DNA aislated from a protozoan parasite 1 year ago. I did various PCR successfully. Now I have done some more PCR with the same DNA samples and same primers, all conditions are the same as in the past but, nothing work. I can't get good results. Someone has any idea what could be happening? My primers were diluted again for trying new PCR but nothig work. Help!!!!

Did you do the first batch of PCR that worked a year ago? Most likely your DNA has degraded since then. How did you keep the DNA? If it was at -20C then generally your DNA is only good for up to half a year at most. At -80 you'll have better chances, but you still have to be careful when thawing it.

Seconded. Depending on the type of PCR and the way of storage a year old DNA can yield lousy results. Of course, the remaining components should also be relatively fresh.