With the determination and annotation of the human genome, it has become very clear that a significant fraction of the human genome (about 40% of the 58% of known genes determined by Venter et. al. and published in Science, 291, 1335, 2001) is devoted directly or indirectly to signal transduction processes. These include signal molecules, receptors, kinases, regulators, protooncogenes and ion channels. The chart below shows the relative distribution of over 26,000 genes of known function (with 42% still of unknown function.
Figure: Distribution of Molecular Functions of 26,383 Genes