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Gene expression comparison between different species(!) - (Jun/26/2005 )

Hi all experts,
I am a green grass to gene expression analysis. I work with qPCR to analyze gene expression. My work usually compares gene expression difference between treated and non-treated(control) groups, by calculating the ratio(Treated/non-treated). Before calculating this ratio, the values of both treated samples and controls are all normalized firstly to the house-keeping gene(HKG).
It sounds like an IQ question. Recently I get a challenging job. I have to compare the expression levels of a certain gene in different species(!). I have subjected all the samples to the HKG. It shows me the absolute expression level is different between my samples. Let's say, two samples(A and B ) have the same expression level of 100 copies of the HKG expression, C has a expression of 150 copies. I assume that this variation is due to the up-stream steps and all gene expressions are parallel to the HKG level. qPCR shows me A has 200 copies of gene-of-interest, B has 300 copies and C has also 300 copies. And A, B and C are different vertebrate sorts. Where I have to take consideration and caution of before I can say B has the highest expresson level, whereas A and C are the same?
Do I need to know the exact molecule number/ul of my samples?
Thanks a lot in advance.
_________________
Ribosoul

Knowledge makes life better

-Ribosoul-

Use the DeltadeltaCt method. this method gives you an expression level normalized by HKG expression. You can compare samples from different species with different HKG expression levels.

-Tomy-