Chromosome identi®cation and assignment of DNA clones in the dog using a red fox and dog comparative map F. Yang 1 , B. S. Milne 1 , C. Schelling 2 , G. Dolf 3 , J. Schla Èpfer 3 , M. Switonski 4 , D. Ladon 4 , A. Pienkowska 4 , A. A. Bosma 5 , D. R. Sargan 1 & M. A. Ferguson-Smith 1 1 Centre for Veterinary Science, Department of Clinical Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge, CB3 0ES, UK; Tel: (44) 1223 766498; Fax: (44) 1223 337610; E-mail: fy@mole.bio.cam.ac.uk; 2 Federal School of Technology, Zurich, Switzerland CH-8092; 3 Institute of Animal Breeding, University of Berne, 3012 Berne, Switzerland; 4 Department of Genetics and Animal Breeding, Agricultural University ofPoznan, Wolynska 33, 60-637 Poznan, Poland; 5 Department of Cell Biology and Histology, Faculty of Veterinary Medicine, University of Utrecht, Utrecht, the Netherlands  Correspondence Received 16 September 1999; received in revised form and accepted for publication by A. Sumner 17 November 1999 Key words: comparative mapping, cosmid, DAPI-banded idiogram, domestic dog, FISH, red fox Abstract We have developed a novel method for identifying dog chromosomes and unambiguously mapping speci®c clones onto canine chromosomes. This method uses a previously established red fox/dog comparative chromo- some map to guide the FISH mapping of cloned canine DNA. Mixing metaphase preparations of the red fox and dog enabled a single hybridization to be performed on both species. We used this approach to map the chromosomal locations of twenty-six canine cosmids. Each cosmid contains highly polymorphic microsatellite markers currently used by the DogMap project to compile the canine linkage map. All but two cosmids were successfully assigned to subchromosomal regions on red fox and dog chromosomes. For eight cosmids previously mapped on dog chromosomes, we con®rmed and re®ned the canine chromosomal assignments of seven cosmids and corrected an erroneous assignment regarding cosmid CanBern1. These results demonstrate that the red fox and dog comparative chromosome map can greatly improve the accuracy and ef®ciency of chromosomal assignments of canine genetic markers by FISH. Introduction Physical mapping by ¯uorescence in-situ hybridiza- tion (FISH) plays an important role in the develop- ment of genetic and physical maps in mammals. The assignment of genetic markers to speci®c chromo- somes allows the linkage and syntenic groups con- taining these markers to be anchored to speci®c chromosomes ± the naturally occurring linkage groups. Although chromosomal assignment of genet- ic markers by FISH has been successful in most mammals mapped so far, it has been complicated in the dog genome project by the dif®culty of karyotyp- ing dog chromosomes. The domestic dog ( Canis familiaris) has a karyotype of 2n  78, with all autosomes being acrocentric (Selden et al. 1975). So far, only the ®rst 21 autosomes and the sex chromo- somes have been standardised internationally (Swi- tonski et al. 1996). It is suggested that cytogenetic identi®cation of at least the smallest 17 of the 38 pairs of autosomes will rely on traditional banding as well as indirect identi®cation with speci®c probes, Chromosome Research 8: 93±100, 2000. # 2000 Kluwer Academic Publishers. Printed in the Netherlands 93