Simple DNA repeats and sex chromosome differentiation in Asellus aquaticus (Crustacea, Isopoda).

The crustacean isopod species Asellus aquaticus does not usually have recognizable sex chromosomes. We previously identified a Y chromosome marked by two heterochromatic bands in some males of a population from the Sarno river near Naples. In this work we used oligonucleotide probes to test the presence and possible sex-specific distribution of five simple repeat motifs in the genome of male and female individuals from the Sarno population. The five oligonucleotide probes were hybridized to enzyme-restricted genomic DNAs and the chromosome location of two probes was tested using fluorescence in situ hybridization. Our results show that only the (TCC) repetitive simple sequence has a sex-specific hybridization pattern and presents a significant accumulation on the Y chromosome in the region included between the two heterochromatic areas. Moreover the GGAAT sequence is not present in the genome of A. aquaticus in any detectable quantity.