If you're making your own, depending on the mix you're using and the concentration of your extracted DNA it should look something like this:
Preparing a 20uL (TOTAL including DNA)
1. Buffer mix (if you're using a 10x dilute it 10 times etc...) ml
2. Forward primer 1uL
3.Reverse primer 1uL
4.Taq polymerase 0.5-1uL
5. Water
6. Template DNA 1mg (again the volume will depend on the DNA concentration that you have) X uL
Calculate these volumes up until ingredient 5, which is the DNA. So if you require 2uL of DNA solution to get 1ug of DNA ingredients 1 through 5 should have a total of (20-X)uL.
IF you need 20 reactions prepare 10% more master mix due to pipette inaccuracies and aliquot it in pcr reaction tubes. THEN add the amount of DNA necessary to add 1ug of DNA AND have a total volume of 20uL.
Run your PCR. In case you need a bigger or smaller reaction volume adjust accordingly the amount of water.
This is just a guideline and you might need to adjust it,
If you are making 20 ul reaction mixture, then add 4 ul of your master mix and then 1-1 ul of your forward and reverse primers (10 pmole/ul) and 1 ul of DNA. rest of the volume is d/w.
Hi Aalaa, with a 5x enzyme mix, for a 20 ul reaction you would add 4 ul of your mix, 1-2 ul of your forward and reverse primers (final concentration 250 - 300 nM final initially). I would strongly suggest to add a higher volume of DNA or cDNA than 1 ul as I find that there is too much error in technical replicates using this volume. So I would suggest to add about 4-5 ul of DNA. Then you can complete with water your master mix to get 20 ul.
The fact that you "dilute" your DNA won't matter in the end as you'll be adding less water to your master mix, so in the end, the amount of DNA will be the same. In other words, if you add 4 ul of DNA instead of 1 ul, dilute your original DNA 4x with water and then add 4 ul of this DNA to your PCR reaction. Hope this make sense for you.