Clustering of gene expression. A. The log2 of FPKM for each gene was used for hierarchical analysis of the heat map at each of the six selected developmental stages (CO, GC, MS1, MS2, MS3 and MS4). The heat map illustrates that 10,158 expressed genes were classified into 132 gene-expression clusters generated by clustering. The colors correspond to the log2 of FPKM values, ranging from bright blue to red. B. Log2 average gene-expression levels of the top 18 clusters identified. The number of genes in each cluster is bracketed.