Parent of origin expression status of X-linked loci on the wallaby and opossum X chromosome. The position of SNPs on the wallaby X chromosome was predicted using the physical map  and opossum sytenic blocks with 1:1 orthologous genes. SNPs in wallaby intergenic regions are labelled as X_Locus 1-17, with the name of the neighbouring gene in brackets. SNPs for which position could not be resolved in wallaby are shown in dotted lines. Read depth at each position is given in the ‘Coverage’ column. Yellow boxes identify SNPs within the same scaffold. Orange represents genes in the newest X stratum in marsupials, genes highlighted in green are in the oldest stratum, genes highlighted in black could not be assigned a stratum, and the stars (*) beside gene names denote predicted new or old genes (see Methods). Parent of origin expression of the opossum genes were obtained from . Bars represent the percentage of reads derived from the maternal (pink) or paternal (blue) allele. The dark blue stars are the predicted locations of RSX in each species.