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This study presents a whole-genome comparison of human and a representative of the Afrotherian clade, the African elephant, generated by reciprocal Zoo-FISH. An analysis of Afrotheria genomes is of special interest, because recent DNA sequence comparisons identify them as the oldest placental mammalian clade. Complete sets of whole-chromosome specific painting probes for the African elephant and human were constructed by degenerate oligonucleotide-primed PCR amplification of flow-sorted chromosomes. Comparative genome maps are presented based on their hybridization patterns. These maps show that the elephant has a moderately rearranged chromosome complement when compared to humans. The human paint probes identified 53 evolutionary conserved segments on the 27 autosomal elephant chromosomes and the X chromosome. Reciprocal experiments with elephant probes delineated 68 conserved segments in the human genome. The comparison with a recent aardvark and elephant Zoo-FISH study delineates new chromosomal traits which link the two Afrotherian species phylogenetically. In the absence of any morphological evidence the chromosome painting data offer the first non-DNA sequence support for an Afrotherian clade. The comparative human and elephant genome maps provide new insights into the karyotype organization of the proto-afrotherian, the ancestor of extant placental mammals, which most probably consisted of 2n=46 chromosomes.

The differences in chromosome number between Otolemur crassicaudatus (2n = 62) and Galago moholi (2n = 38) are dramatic. However, the total number of signals given by hybridizing human chromosome paints to galago metaphases is similar: 42 in O. crassicaudatus and 38 G. moholi. Many human chromosome homologs are found fragmented in each species, and numerous translocations have resulted in chromosomal syntenies or hybridization associations which differ from those found in humans. Only 7 human autosomes showed conserved synteny in O. crassicaudatus, and 9 in G. moholi. Both galago species have numerous associations or syntenies not found in humans: O. crassicaudatus has 11, and G. moholi has 21. The phylogenetic line leading to the last common ancestor of the two galago species accumulated 6 synapomorphic fissions and 5 synapomorphic fusions. Since the divergence of the two galago species, 10 Robertsonian translocations have further transformed the G. moholi karyotype, and 2 fissions have been incorporated into the O. crassicaudatus karyotype. Comparison with other primates, tree shrews, and other mammals shows that both galagos have karyotypes which are a mixture of derived and conserved chromosomes, and neither has a karyotype close to that of the proposed ancestor of all primates. Am J Phys Anthropol 117:319-326, 2002. Published 2002 Wiley-Liss, Inc.

Black rats are of outstanding interest in parasitology and infective disease analysis. We used chromosome paints from both the mouse ( Mus musculus) and the Norway rat ( Rattus norvegicus) to characterize the genome of two Black rat subspecies from Italy. Both subspecies have two large metacentrics (n. 1, 4) not present in the Norway rat (2n = 42). Rattus rattus rattus has a diploid number of 2n = 38, while Rattus rattus frugivorous has two small metacentric "supernumerary" or B chromosomes for a diploid number of 2n = 38 + 2B. The 21 mouse paints gave 38 signals on the R. r. rattus karyotype and 39 signals in the R. r. frugivorous karyotype. The two metacentrics, not present in R. norvegicus, were hybridized by mouse 16/1/17 and mouse 4/10/15. These chromosomes are homologous to: RRA1 = RNO 5/7, and RRA4 = RNO 9/11 and not "4/7" and "11/12" as previously reported. Furthermore, the synteny of Chr 13 of the R. r. frugivorous with R. norvegicus Chr 16 and mouse Chrs 8/14 is not complete, because there is a small pericentromeric insertion of RNO Chr 18 (mouse Chr 18). If we consider only the two metacentrics, RRA1 and RRA4, the principal differences between R. norvegicus and R. rattus, then we can propose the derived synteny of 124 genes in the black rat. A comparison of the Z index between rats and mice shows an acceleration of genomic evolution among genus, species, and subspecies. The chromosomal differences between R. r. rattus x R. r. frugivorous suggest that they may be classified as different species because hybrids would produce 50% unbalanced gametes.