Genome maps 10. Comparative genomics. Mammalian radiations. Wall chart.

![Figure][1] Traces of evolutionary history appear in functional morphology and DNA sequences of living and extinct species. These remnants of the past can lead to insights into the relationships among extant groups of animals, the forces driving evolution, and the utility of animal models for studying human disease. We present below one evolutionary interpretation of the still-disputed hierarchy of surviving placental mammalian orders (excluding monotremes and marsupials), a synthesis of accumulated molecular and morphological inferences. The time scale is derived largely from molecular data; indicated fossil remains are much younger, raising controversies around the precise age of mammal ancestors. The tips of the phylogenetic tree depict genomes for 21 representative species from 11 orders, which are labeled on the vertical lines. These examples show genome-wide homology alignments assessed by comparative gene mapping or direct visualization of chromosome painting, in which fluorescently labeled, individual chromosomes are hybridized to chromosomes from distantly related species. Species were selected to maximize the number of orders represented and to illustrate patterns of genome conservation. The 24 human chromosomes are distinguished by 24 colors, and regions of human chromosome homology in other species are indicated by color and human chromosome number (for example, cat chromosome A1 contains gene stretches homologous to human chromosomes 5 and 13). Selected gene homologs in each species represent a subset of extensive comparative gene mapping data; thus genes listed may not reflect the extreme borders of the conserved segments. Gene orders have been determined in human, cat, pig, sheep, rat, mouse, and zebrafish; in other species the genes are listed in the order in which they appear in humans. The zebrafish map, including 25 linkage groups not yet assigned to the 25 chromosomes, is presented to illustrate the array of gene segments conserved for 450 million years. Further information and discussion of dissenting views of mammalian evolution can be found in this issue of Science and the associated web site at ![Figure][1] CREDITS Science Coordinators: Barbara R. Jasny and Pamela J. Hines Authors: Phylogenetic tree Stephen J. O'Brien, National Cancer Institute, Frederick, MD, USA; John F. Eisenberg, University of Florida, Gainesville, FL, USA; Michael Miyamoto, University of Florida, Gainesville, FL, USA; S. Blair Hedges, Pennsylvania State University, University Park, PA, USA; Sudhir Kumar, Arizona State University, Tempe, AZ, USA; Don E. Wilson, Smithsonian Institution, Washington, DC, USA. Genomic maps Stephen J. O'Brien, Marilyn Menotti-Raymond, William J. Murphy, William G. Nash, Leslie A. Lyons, Joan C. Menninger, Roscoe Stanyon, Johannes Wienberg, Neal G. Copeland, Nancy A. Jenkins, National Cancer Institute, Frederick, MD, USA; Joel Gellin, Martine Yerle, Institut National de la Recherche Agronomique, Castanet-Tolosan, France; Leif Andersson, Swedish University of Agricultural Sciences, Uppsala, Sweden; James Womack, Texas A & M University, College Station, TX, USA; Thomas Broad, AgResearch, Invermay, Mosgiel, New Zealand; John Postlethwait, University of Oregon, Eugene, OR, USA; Oleg Serov, Institute of Cytology and Genetics, Siberian Branch of the Academy of Sciences of Russia, Novosibirsk, Russia; Ernie Bailey, University of Kentucky, Lexington, KY, USA; Michael R. James, Wellcome Trust Centre for Human Genetics, Headington, UK; Takeshi K. Watanabe, Otsuka GEN Research Institute, Tokushima, Japan; Matthew J. Wakefield, Jennifer Marshall Graves, La Trobe University, Melbourne, Australia. Design and Art Direction: C. Faber Smith Graphics: Nathalie Cary Illustrations: Katharine Sutliff Production Assistance: Holly Bishop, Leslie Blizard, Inja Lin, Darcel Pugh Proofreading: Harry Jach [1]: pending:yes