Distribution of C-band heterochromatin in the ZW sex chromosomes of European and American eels (Anguillidae, Teleostomi).

The ZW sex chromosomes of the European eel, Anguilla anguilla, and the American eel, A. rostrata, were examined with C-band and fluorescent staining to demonstrate the C-band heterochromatin. The W as well as Z chromosomes in both species are C-band negative except for a small amount of C-band heterochromatin in the centromeric region, in contrast to the W or Y elements of most other vertebrates. No fluorescing W-associated body is evident either in interphase nuclei or in metaphase plates. The ZW chromosomes of the two species have substantially similar size, morphology, and patterns of C-band heterochromatin. Karyologic and evolutionary implications are discussed.