Out of these ancestral genes, probably only CEACAM1 ancestors gave rise to massive gene expansions in a orderspecific manner [3] . The CEACAM1-related genes form compact clusters next to CEACAM1 and near the CD79A gene. In rodents even a third locus (around the Hif3a gene) has been encroached by amplified CEACAM1related genes. With analysis of the CEA family in a third order (carnivores), the inversion event observed for the chromosomal region flanked by Cd79a and Lipe can now be decided to have happened in the rodent rather than in the primate lineage, since the order of genes in this locus is conserved between humans and dogs ( Figure 1 ).