Currently, I am working on some microarray data analysis (ICGC database) and I need to calculate log ratio between gene expression of tumor tissue and normal tissue. I have somthing like this:
patient1 - normal tissue: gen1: -0.78, gen2: 0.487, gen3: 1.147 and so on
patient1 - tumor tissue: gen1: 1.87, gen2: 1.47, gen3: -0.147 and so on
Equation of log ratio is: LR = log2(P/Q), in my case P - tumor tissue, Q - normal tissue
LR(gen1) = log2(-0.78/1.87)
Any idea how to dealing with negative value in log? Or I am doing this on a wrong way?