EMERGING PATTERNS OF COMPARATIVE GENOME ORGANIZATION IN SOME MAMMALIAN-SPECIES AS REVEALED BY ZOO-FISH

Although gene maps for a variety of evolutionarily diverged mammalian species have expanded rapidly during the past few years, until recentl y it has been difficult to precisely define chromosomal segments that are homologous between species. A solution to this problem has come Fr om the development of Zoo-FISH, also known as cross-species chromosome painting. The use of Zoo-FISH to identify regions of chromosomal homo logy has allowed the transfer of information from map-rich species suc h as human and mouse to a wide variety of other species. From a Zoo-FI SH analysis spanning four mammalian orders (Primates, Artiodactyla, Ca rnivora, and Perissodactyla), and involving eight species (human, pig, cattle, Indian muntjac, cat, American mink, harbor seal, and horse), three distinct classes of synteny conservation have been designated: ( 1) conservation of whole chromosome synteny, (2) conservation of large chromosomal blocks, and (3) conservation of neighboring segment combi nations. This analysis has also made it possible to identify a set of chromosome segments (based on human chromosome equivalents) that proba bly made up the karyotype of the common ancestor of the four orders. T his approach provides a basis for developing a picture of the ancestra l mammalian karyotype, but a full understanding will depend on studies encompassing more diverse combinations of mammalian orders.