Fig. 10.

Functional biased pattern of gene loss by coelimination of genes of the retinoic acid metabolic gene network (RA-MGN). The losses of the genes Rdh10, Rdh16, Bco1, Aldh1a, and Cyp26 occurred in a context of low mutational robustness with no compensatory rerouting for the synthesis of atRA by any alternative pathway, and likely in an scenario of regressive evolution in which the loss of RA-signaling and its nuclear receptor genes (e.g., RAR, PPAR) did not imply major phenotypic changes related to RA-target genes, such as Hox1 that show the same expression pattern in Oikopleura dioica and ascidians.