ABSTRACT
The molecular markers provide information on the karyotype evolution in the class of vertebrates and identify some chromosome regions as sites in which particular repeated DNA sequences accumulate. The physical distribution of the different types of molecular markers used in elasmobranch cytogenetics provide valuable information about genome organization and the evolutionary status of a given species. This chapter reviews the data collected using the molecular approach based on both physical chromosome mapping and genomic hybridization of some multicopy genes and repetitive sequences in Chondrichthyes. The studies on genome composition have revealed marked differences between cartilaginous fishes and teleosteans in the ratio of the amount of GC-rich DNA to the total increase in genome. Elasmobranch fishes are considered to be ancient vertebrates, having diverged from the stem lineage leading to crown vertebrates early in the diversification of craniates. The molecular techniques reveal specific linkage groups on definite chromosome pairs in the Elasmobranch genome.
