Fig. 6.

In vertebrates, erk2 genes are larger than erk1 genes. Genomes from vertebrates were screened for the presence of the full length sequences of erk genes, and then the size from ATG to stop codon was calculated in kilobases. In teleosts and mammals, animals for which both erk1 and erk2 genes sequences are available were preferred, only one pair of mammalian erks is not from the same animal. Full erk1 gene sequence of coelacanth (L. chalumnae) is not available. For teleosts, the erk genes of T. fubripes and T. nigroviridis were not taken into account due to their known extreme genome compactness that would skew the size distribution (smallests vertebrate genomes) their erk1 gene size being 5 and 3.9 kb respectively and their erk2 gene size being 9.7 and 10 kb respectively). For teleosts and mammals, the average sizes of the genes are written on the upper left side of the graphical bars, and the p-value that evaluates the statistical significance of the difference between erk1 and erk2 gene sizes is indicated. For reptiles, the fold difference between the sizes of erk1 genes and erk2 genes is indicated on top of the bars with an arrow. Silhouettes are from http://phylopic.org/