Cytogenetics applied to domestic animals is a useful biotechnology to be applied in the genetic improvement of livestock. Indeed, it can be used to select reproducers free chromosome abnormalities which are responsible for abnormal body conformation (aneuploidy), lower fertility (balanced chromosome abnormalities) or sterility (sex chromosome abnormalities). Cytogenetics may also be applied to assess environmental pollution by studying animals living in hazardous areas and using them as biological indicators (sentinels). Chromosomes also represent optimal biological structures to study the evolution among related (bovids) and unrelated (bovids humans) species, especially using comparative FISH-mapping which is one of the most powerful tools to establish the correct order of loci along chromosomes. These comparisons allow us to transfer useful information from richer genomes (human) to those of domestic animals. Moreover, the use of specific molecular markers and the FISH-tech nique on both mitotic and extended (fiber-FISH) chromosomes, has heralded a new era of cytogenetics, allowing swift extension of genetic physical maps, better anchoring of both linkage and RH-maps to specific chromosome regions, and use in a variety of applications (clinical cases, embryo a