Organization of the 29 SNC and 21 XNC genes including pseudogenes, indicated by Ψ. SNC genes are located on chromosome 8 and XNC genes are located on two different scaffolds encompassing a total of 0.8 Mbp (drawn to scale). Scaffold numbers for X. laevis are based on the Xenopus laevis Genome project http://xenopus.lab.nig.ac.jp, XenVis 2.0 assembly and chromosome number and gene location for X. tropicalis are based on the USSC genome bioinformatics Xenopus genomes hosted at NIMR (http://genomes.nimr.mrc.ac.uk, July, 2013 assembly. Expressed genes, as supported by EST identifications and/or RT-PCR, are indicated by * and arrows indicate transcriptional orientation. Flanking non-class Ib genes are shown as white boxes. Orthologous relationships defined by multiple sequence alignments and phylogenetic analysis between XNC and SNC genes are indicated by dashed lines.