A modified Welch F statistic was used for ANOVA. For each gene, regressed error estimates were substituted for observed error estimates. The substitution is justified by the lack of consistency among the most and least variable genes at each time point. Regressed error estimates were abundance-dependent pooled error estimates that represented a median error estimate from a window of genes of similar abundance to the gene of interest. A randomization test was used to compute the probability Pg of the observed F statistic for gene g under the null hypothesis that developmental time had no effect on expression. P-values were not corrected for multiple testing.
Strictly maternal class (SM): genes that are the subset of maternal genes that are not also classified as embryonic.