Hi Nagalakshmi

I don't know what volume your 7-20ng are in but if it is per microliter it is fairly low as a yield from standard isolations. It may mean you have very clean DNA which always helps for PCR. WHy do you have 2 concentration ranges, and why do you say you have concentration and give the units for amounts? Are the templates plasmids, genomic DNA, cDNA? What do you want to do with the PCR product?

Anyway, you could start with 1-2 mul per 20 mul PCR for diagnostics PCR, maybe dilute a bit more in water if you fear that there are inhibitors in your prep.

Let us know how it goes.

I think we need more information to give a useful answer. For example, if your template is a plasmid, that means that every copy of the plasmid has one copy of your template. On the other hand, if your template is genomic DNA of a single gene, then there is only one (*n) copies of your gene per genome. As such, 10ng of plasmid is more than enough! On the other hand, 10 ng may be low if you are looking for a single gene in a large genome.

Optimal amounts of template DNA in the 50 µl reaction volume are in the 0.01-1 ng

That depend of the nature of your DNA,It's genomic DNA, from plasmid...??

The correct way to estimate the amount of template, is by the number of copies instead of weight. In theory a single copy of the mold is enough. But in practice, is used between 100 and 10,000 copies of the template. Therefore, the amount of template to be used depends on the molecular weight of the DNA. For example, for genomic DNA from eukaryotic cells are used between 0.025 to 0.25 ug .