Pairwise correlation analyses and principal component analysis

log₂-transformed gene expression levels of 23,135 REG were used to compute the pairwise correlations between transcriptomes at different developmental time points using the R command cor(data, use = “pairwise.complete.obs”, method = “Pearson”). To further show the strong temporal relationship between our samples, we performed a PCA using the function princomp (Sigg and Buhmann 2008) in R with default parameters. The loadings corresponding to the PC2, PC3, and PC4 appeared to be periodical patterns.