Fig. 2. Transcriptional transitions during Dictyostelium development. Cells were starved on filters and samples collected at 2-hour intervals as indicated. (A) The dendrogram represents the dissimilarity between the RNA samples based on all values of gene expression for each time point. The two most dissimilar groups of samples are indicated as red and green clades, which correspond to the unicellular and the multicellular stages, respectively. (B) The color chart represents the pattern of expression for genes that are highly regulated during development. The order of 2021 genes from top to bottom was determined by the fit between their pattern of expression and the function (y=x/12–1). The chart and the dendrogram are derived from an average of four independent experiments from different strains and growth conditions. The positions of several previously characterized genes are indicated: A, cotA; B, cotB; C, cotC; D, cprD; P, pspA; V, vegetative ribosomal genes. The supplemental data (http://dev.biologists.org/supplemental/) contains a complete list of the genes. Each column represents a time point (hours) and each row represents an array target. The color scale represents the standardized log₂ of the ratio between the tested sample and the standard relative to the gene mean, where blue indicates a lower-than-average level of expression and yellow indicates a higher-than-average level of expression.