gene expressional analysis - (Jan/05/2011 )

hi all

I am new to this expressional studies and I need a little clearance of my doubts from u all. I am supposed to perform the expressional analysis of target genes after RT-PCR by comparing with the band intensities of the internal control like the GAPDH primers. I am supposed to see the change in the expressional level for a certain gene at different stress levels by comparing with the housekeeping gene under same condition. I am confused as to how to measure the density analysis of the band intensities and plot a comparison graph. Is there any free software that can give the comparison between the band intensities of the target and the housekeeping gene?

Plz help me .

Thanks in advance

Try imageJ. You should do a semi-quantitive PCR (target or cycle "dilution").