The case of the dissapearing DNA - (Jan/12/2008 )

Hello everyone,
I had isolated this human genomic DNA from Blood in Dec 2006. It kept giving very nice PCR results when 2 microlitre was used in 50 microlitre PCr reaction, but now it takes 10 microltre to get a faint band on agarose gel. what is happenieng to it and how do i save it?

freeze thaw cycles affect quality of DNA preparation and i assume it makes breaks points in the molecule.
Also, considering the fact that a nuclear protein extract loose activity after long periods there is a possibility that some degradation occurs witihin -80° freezer.

Also did you check OD to see what it tells now ?

You probably simply have a very small concentration of DNA in your genomic prep. If you are only using it for PCR, that is fine. Don't worry about seeing it on the gel. I often dilute my genomic template 1:100 before using it for PCR anyway. It is likely enough DNA for a PCR template, just not enough to be visualized. You cannot check the integrity as easily at such a concentration, but if you are still getting PCR products, I wouldn't worry.