Gene clustering in the endometrium: Gene expression profiling across the menstrual cycle. The Heatmap represents relative gene expression levels in the endometrial samples across the menstrual cycle. Each horizontal line represents a single gene, and each column represents a single sample. Samples cluster by cycle phase (bar at bottom of the Heatmap: proliferative (red), early-secretory (light blue), mid-secretory (olive), late secretory (purple) and ambiguous samples (dark blue). Relative expression of each gene is color-coded: high (red) or low (blue), as indicated in the color legend on the left side of the figure. Hierarchical clustering reveals sample clustering into cycle phases and unique molecular profiles. Adapted from , with permission.