Xenarthra, as the probable earliest offshoot of the placental tree, represents a key taxon for understanding mammalian phylogeny. To gain further insight into the chromosomal evolution and genome organization of the xenarthrans, we have established the first genome-wide comparative chromosome map between human and the 6-banded armadillo (Euphractussexcinctus, 2n = 58), a basal species on the Xenarthra branch, by reciprocal cross-species chromosome painting. In total, 22 human autosomal paints revealed 41 homologous segments in the euchromatic genome of E. sexcinctus. Our results provide further support for the notion that the 2 human homologous segmental associations, i.e. HSA 2/8 and 7a/10p, could constitute the synapomorphies that unite the xenarthrans. Moreover, we propose that the putative ancestral Xenarthra karyotype closely resemble the 2n = 54 karyotype of the E. sexcinctus, consisting of the equivalents of HSA1p, 1q, 2a, 2b, 2c/8c, 3/21, 4a, 4b/8b, 5, 6a, 6b, 7a/10p, 7b/16p, 8a, 9, 10q, 11, 12a/22a, 12b/22b, 13, 14/15, 16q/19q, 17, 18, 19p, 20, and X. In addition, we have analysed the C-banding patterns of E. sexcinctus, and cloned, FISHmapped and sequenced 7 novel repetitive DNA segments, providing further information on the complexity of genome architecture of E. sexcinctus.
