# How to calculate absolute fold change in expression by realtime PCR - Realtime PCR (Jan/24/2006 )

Hi

I am trying to calculate the absolute fold change for gene expression by realtime PCR. Usually I subtract ct value of reference sample from the target and normalise against the value of house keeping gene obtained the same way that is subtracting it from thet target values of that sample and value that comes after this is the relative value with respect to the control. Now how to convert this difference in ct values of target sample to fold change ,does any one know any formula. Considering that 10 fold change in expression is equivalent to 2-3cycles difference in amplification.

-farnish-

if your efficiency is close to 1, then 1 Ct value = 2-fold change, right?

-aimikins-

QUOTE (aimikins @ Jan 25 2006, 09:39 AM)

if your efficiency is close to 1, then 1 Ct value = 2-fold change, right?

Yes exactly . And to know exact absolute number of copy numbers in terms of fold change I need to clone and then do the PCR.

FN

-farnish-