title: The origin of human chromosome 1 and its homologs in placental mammals.
abstract: Developing ordered gene maps from multiple mammalian species coupled with chromosome-painting data provide a powerful resource for resolving the evolutionary history of chromosomes and whole genomes. In this work, we recapitulate the evolutionary history of human chromosome 1 and its homologs in placental mammals, putatively the largest physical unit in the ancestral placental genome. Precise definition of translocation exchange breakpoints in human, carnivore, cetartiodactyl, and rodent-ordered gene maps demonstrate that chromosome breakpoints, previously considered as equivalent, actually represent distinct chromosome positions and exchange events. Multidirectional chromosome painting, using probes from homologs to chromosome 1 in seven mammal species from six orders of placental mammals, confirm the gene-mapping results and indicate that the multiple human chromosome 1 homologs in these species are derived from independent fissions of a single ancestral chromosome. Chromosome painting using human chromosome 1 probes identifies a single human chromosome 1 homolog in phylogenetically distant taxa, the two-toed sloth, cetaceans, and higher primates. The diverse phylogenetic occurrence of a single Hsa1 synteny among the major clades of placental mammals suggests that human chromosome 1 represents an intact ancestral chromosome, which was variously fissioned in the majority of placental species. We find that the number of human chromosome 1 fissions in a specific lineage reflects its general rate of genomic evolution. Further, historic chromosome exchange appears to have been disproportionately clustered in two breakpoint hotspots on the long arm.
authors.affiliation: Laboratory of Genomic Diversity, National Cancer Institute, Frederick, Maryland 21702, USA. murphywi@mail.ncifcrf.gov
authors.forename: William J
authors.initials: WJ
authors.lastname: Murphy
authors.forename: Lutz
authors.initials: L
authors.lastname: Frönicke
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: O'Brien
authors.forename: Roscoe
authors.initials: R
authors.lastname: Stanyon
mesh_terms: D000818:Animals; D002415:Cats; D002417:Cattle; D002874:Chromosome Mapping / Q000379:methods / Q000706:statistics & numerical data; D002878:Chromosomes, Human, Pair 1 / Q000235:genetics*; D004285:Dogs; D019143:Evolution, Molecular; D014644:Genetic Variation / Q000235:genetics; D006801:Humans; D008322:Mammals / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D010920:Placenta; D051381:Rats; D012689:Sequence Homology, Nucleic Acid