(a) Comparisons of Fiber lengths of the three cotton species (left), and growth rate analysis for G. hirsutum and G. arboreum (right). Error bars, mean ± s.d. (b–d) qRT-PCR analysis of primary and secondary cell wall biosynthesis genes using the At- (indicated by blue lines) or A-originated (red lines) copy as the template. UER, UDP-4-keto-6-deoxy-D-glucose 3,5-epimerase 4-reductase; UGP, UDP-D-glucose pyrophosphorylase; UGD, UDP-D-glucose dehydrogenase. See Supplementary Table 19 for gene-specific primers. Error bars, mean ± s.d. (e) The evolution of regulatory mechanisms for fiber-specific and highly expressed genes from the At subgenome.