The dog CEACAM1-related genes are arranged head to tail, like the KIR genes in the human KIR locus [38, 39] . Such an arrangement was found to facilitate unequal crossing over leading to gene expansion and generation of multigene families [40] . Furthermore, the KIR gene family is subject to birth-and-death evolution, domain shuffling and mutational changes [41] . Our analyses indicate that the CEA gene family evolved similarly. One characteristic for this kind of evolution is the presence of multiple pseudogenes, which also exist within the canine CEACAM1like gene locus (CEACAM26, CEACAM27).