Comparison of expression profiles of selected genes during meiotic development and progress in meiotic differentiation. (a) Experimentally monitored and (b) schematically represented timing of meiotic landmark events. (c, d) Clustered gene expression patterns where rows correspond to a gene and columns correspond to time points after transfer from YPA to sporulation medium. Genes were clustered according to similar temporal expression patterns as indicated in the boxes at the left of each heatmap. The transcript levels in the sporulating SK1 MAT a/α strain were compared to the sporulation-deficient SK1 MATα/α strain in YPA, and at 6 h and 10 h after transfer to sporulation medium. The significance levels of the observed differences between both strains were calculated in pairwise t-tests and are indicated next to panels that show expression levels. Genes with annotated meiotic functions are shown in C (GO terms: pre-meiotic DNA synthesis, reciprocal meiotic recombination, sporulation, ascus spore wall formation). Genes coding for enzymes in the central carbon metabolism are shown in d. Log2-scaled expression levels of each gene were scaled to have a mean of zero and a standard deviation of one. Each time point is colored according to signal strength ranging from low (blue), over medium (yellow), to high (red) expression. The expression data represent the average of two independent experiments. (Abbreviations: MI and MII denote the first and the second meiotic division, respectively; cfu = colony forming units; His+ = colonies that grow without histidine supplementation).