Gene expression during the HeLa cell cycle. Each gene corresponds to a row, and the time point (minutes) for each column is denoted. The magnitude of mRNA expression ratio for each gene is represented by different colours. Red indicates mRNA abundance; green indicates a dearth; and gray indicates absence of the data. On the top bar(s), S phase and the time of mitoses (the arrows) are indicated, which was estimated by flow cytometry and BrdU (bromodeoxyuridine) labeling previously.