Clustering result: Mixture of Gaussians. The similarity of overall patterns in the clustering result of the MoG is explained by the developmental stages investigated. The major phenomena are depletion of maternal mRNA (maternal genes) and start of the embryonic transcriptional machinery during embryogenesis at time point 3 hours (zigotically expressed genes). In the clusters with zigotically expressed genes, we observe two main periods of activation: 3–4 hours for cluster U1 to U5, and 7–8 h for clusters U8 to U11. In the clusters with maternal genes, we observe under-expression of genes at several time periods: 3–4 h in clusters U21 to U28; 4–5 h for clusters U17 to U20; 6–7 h for cluster U16; 7–8 h for clusters U12 and U13; and 9–10 h for cluster U15.