Today i was confused with a very simple problem !! How to determine up and down regulated genes from log2 values. I would like to clear this problem:
Suppose 2 gene expression values A,B (treatment):
Foldchange is B/A => FC=1.5 or greater is Up regulated , and if the values were B=10,A=15 we'll have FC=0.66 it means all values less than 0.66 will be down regulated.
For log2-foldchange, its formula is
which then all values greater than 0.5849 were be up regulated and all values less than -0.5849 (or FC =0.666) were be down regulated genes, protein or etc.
For calculating Fold change from log2 just do , Power(2, log2_Value), Power(2, 0.5849)=1.5