I guess because since it is a cloned gene, you know its exact size and concentration and therefore can use this for the assumption of the expression of your gene of interest.

And since it is cloned you can produce big amounts of it

Dear Simon Flueckiger thank you very much.

Sure, one of the reasons for cloning is multipling an gene/DNA fragment. But in Quantitative PCR as the biological samples increase in number, statndard could be increase as well. Right? I mean we can use the segment as a DNA template (without cloning). So, what is a scintific reason behind that we need to insert a gene of intrest (DNA segment) into a certain plasmid then transfer into E.coli bacteria? It is the my real question!

I absolutely agree. The reason for using a standard is that you know the concentration for a distinct signal (intensity). Titration of this standard allows to chreate a standard curve (which is most often not linear). This - in turn - enable to compare a signal for a sample of unknown concentration to estimate its conc.!

Andreas Eisenreich

Thanks Dear colleague!

Yes, you are totally right. Let me put it in another way. May I just use DNA template (not plasmid) as a standard or to draw a standard curve? if not, please clarify it why?

Also, could you please introduce a source (specially a book) in this regard why we use it, if it is essentially required?? I need to learn that in details.