This function computes the relative expression profiles of all given phylostrata or divergence-strata within a given PhyloExpressionSet or DivergenceExpressionSet.
a standard PhyloExpressionSet or DivergenceExpressionSet object.
For each phylostratum or divergence-stratum the corresponding relative expression profile is being computed as follows:
f_js = ( e_js - e_j min ) / ( e_j max - e_j min )
where e_j min and e_j max denote the minimum/maximum mean expression level of phylostratum j over the developmental stages s. This linear transformation corresponds to a shift by e_j min and a subsequent shrinkage by e_j max - e_j min. As a result, the relative expression level f_js of developmental stage s with minimum e_js is 0, the relative expression level f_js of the developmental stage s with maximum e_js is 1, and the relative expression levels f_js of all other stages s range between 0 and 1, accordingly.
Domazet-Loso T and Tautz D. (2010). A phylogenetically based transcriptome age index mirrors ontogenetic divergence patterns. Nature (468): 815-818.
Quint M et al. (2012). A transcriptomic hourglass in plant embryogenesis. Nature (490): 98-101.
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