Comparative Cytogenetics

Abstract In the pre‐genomics era, the field of comparative cytogenetics was restricted to the comparison of banded chromosome preparations of the species being studied. Subsequent application of molecular biology tools to cytogenetics facilitated the development of molecular cytogenetics. In particular, fluorescence in situ hybridisation ( FISH ) improved our ability to compare genomes at the chromosomal and subchromosomal levels, leading to much more defined knowledge about the processes of gross chromosomal rearrangements that have occurred during evolution. In the past few years, as more whole genomes have been sequenced, the new wealth of genome information alongside enhanced technologies has advanced cytogenetic studies to a resolution far beyond that of the light microscope. This convergence of genome‐integrated resources with conventional cytogenetics catalysed the emergence of cytogenomics. Using a variety of analytical platforms, cytogenomics provides more detailed study of chromosome changes within and between species, with resolution of just a few kilobases. Within the broader field of comparative genomics, comparative cytogenetics has provided opportunities to understand more about our own genome architecture and function, in the context of the dynamic process of speciation and evolutionary change. In the biomedical arena, the field of One Medicine has embraced a comparative approach to expedite gene discovery using appropriate animal models of disease. This article briefly summarises some of the work that has resulted in a greater understanding of the comparative cytogenetics of mammals, especially in the context of their relationship to the human karyotype. Key Concepts Genomes of different species are organised into different chromosome numbers, sizes and morphologies (karyotypes). While karyotypes differ, cytogenetic approaches may be used to make direct comparisons. The emergence of high‐quality genome sequences for numerous species provides new tools to make higher resolution comparisons of the chromosome of such species. Breakpoints along chromosomes that occur in cancer cells may be similar to those associated with speciation. Chromosome changes in cancers may be shared between species, suggestive of an evolutionarily conserved pathogenetic mechanism.