Identification of putative alien (PA), highly expressed (PHX) and moderately highly expressed (PX) genes. For each gene belonging to the HIP1less set (having to few HIP1 motifs for its size) we calculated the codon usage bias against two set of genes: a) the mean codon usage of all genes in the genome B(F|C); and b) the codon usage of ribosomal proteins B(F|RP) which are expected to be highly expressed. Genes with a codon usage suggesting a high (PX) and very high (PHX) level of expression are shown in blue and green respectively. Genes with a codon usage suggesting a xenolog origin (PA) are shown in red. The rest of the genes belonging to the HIP1less set that didn't meet the criteria to be included in PA, PX or PHX sets are shown in gray.