HETEROCHROMATIN CHARACTERIZATION AND DISTRIBUTION IN THE CHROMOSOMES OF 2 POPULATIONS OF IDOTEA-BALTICA-BASTERI AUDOUIN, 1826 (ISOPODA, VALVIFERA)

Two Mediterranean populations of Idotea baltica basteri from Messina a nd Naples showed a set of chromosomes composed by 58 all-biarmed chrom osomes. The heterochromatin was located in the pericentromeric region of the chromosomes, and its composition appeared heterogeneous. In fac t, not all the homologs showed heterochromatin resistant to digestion with three restriction enzymes (Alu I, Hae III and Sau 3A). Moreover, the two populations showed polymorphism in a band of G + C-rich telome ric heterochromatin, which was present only in the population from Mes sina. It is hypothesized that chromosomal polymorphism might reflect t he geographical isolation of the two populations. It is also suggested that a process of diversification is taking place.