Anguilliformes cytogenetics: karyotype characterization and identification of interstitial telomeres and chromosomal polimorphism in Ophisurus serpens (Ophichthidae)

The family Ophichthidae comprises 52 genera and about 290 species of snake eels and worm eels. Among the nine species cytogenetically studied, the 2n is comprised between 38 and 50; the karyotype structure is highly variable between an all acrocentric- and an all biarmed-chromosomes karyotype. Differentiated sex chromosomes, a ZZ/ZWand a multiple XXXX/XXXY system, have been described in two species. In this work, we deepened the karyotype characterization of O. serpens by replication banding that allowed to identify and characterize the chromosomal pairs; furthermore in this species it has been possible to obtain G-bands, hardly achievable in fishes. Heterochromatic C- and endonuclease-bandings allowed to localize and characterize the constitutive heterochromatin in all centromeres, in some paracentromeric regions and in the short arm of pair 19. With all the banding techniques used, this pair showed an interindividual polimorphism in the short arm length between homologous chromosomes, possibly sex related. By FISH, we localized the 45 S and 5 S ribosomal gene families on the short arm of pair 9 and on the short arm of pair 19 respectively; furthermore we localized the telomeric sequences on all telomeres and in some intrachromosomal sites, including the pericentromeric region of pair 19. The presence of repetitive sequences as telomeric sequences and 5S rDNA, could be correlated to the polymorphism observed in the short arm of pair 19.