Distribution of log2 gene expression difference wrt control agent for each treatment agent. For each treatment agent, the probability density of log-2 expression differences is estimated and plotted. In general, yeast cells produce distinct gene expression responses to individual agents. However, some evidence shows the similarity of expression profiles between NaCl and EtOH, the two cytotoxic compounds. Their log-2 expression differences have a similar range and their density plots have similar long left tails compared with those with long right tails, CIS and MMS.