The advent of technologies for the study of gene activity and gene function at a genome level, combined with knowledge of the entire complement of genes within an organism, has now open the door to the study of cellular phenotype in their full complexity - how activities of one pathway affect another and how small perturbations in one pathway are amplified to generate phenotype. This talk is about cloning the protein-coding sequences of the whole human genome and exploration of the functions of proteins involved in cell cycle at systems level.