Karyotypes and Ag-NORs of the mussels Mytilus californianus and M. trossulus from the Pacific Canadian coast

Abstract

[Abstract] The karyotypes and the nucleolus organizer regions (NORs) of “M. californianus” and “M. trossulus” from the Pacific coast are reported here for the first time. The karyotypes show seven metacentric and seven submetacentric chromosome pairs. In “M. californianus”, nucleolar organizer regions appear located in terminal position on the short arm of one metacentric chromosome pair and of one submetacentric. A third Ag-NOR is located near to the telomere region on the short arm of one submetacentric. In “M. trossulus”, Ag- NORs appear terminally located on the short arms of two metacentric chromosome pairs and on the short and long arms of one submetacentric. The comparison of the karyotypes and Ag-NORs among the species of mussels from the Pacific and European coasts shows remarkable differences.