Integrated Comparative Genome Maps and Their Implications for Karyotype Evolution of Carnivores

Comparative chromosome maps record the history of karyotype changes that have occurred during speciation. The rates, types and directions of chromosomal rearrangements as well as phylogenetic relationships between species being compared can be inferred by comparative analysis of the distribution patterns of conserved segments in different phylogenetic lineages (Nadeau and Sankoff, 1998; Yang et al., 2000a). The successful identification of chromosomal homology between species is fundamental for comparative cytogenetic and genomic analysis. Cross-species chromosome painting, being accurate, efficient, and suitable for genome-wide comparison, has become the method of choice for comparative cytogenetics, particularly for comparing distantly related species or species with highly rearranged karyotypes (Scherthan et al., 1994; Yang et al., 1995; Wienberg and Stanyon, 1997; Ferguson-Smith et al., 1998). When combined with chromosome banding and gene mapping, comparative chromosome painting can provide the most accurate comparative chromosome maps for species being compared. Most recently we have been applying this approach to the study of chromosome evolution of carnivores, in particular, the species of the Canidae family, which have the most highly rearranged karyotypes relative to the other carnivores. A series of genome-wide comparative chromosome maps have been established (Yang et al., 1999, 2000a,b; Graphodatsky et al., 2000a,b, 2001; Sargan et al., 2000). The aim of this chapter is to provide an overview of these recent advances in our endeavour to decipher the karyotype evolution of carnivores by integrating the published results together with some of our latest unpublished results.