FATE OF DOT CHROMOSOME GENES IN DROSOPHILA-WILLISTONI AND SCAPTODROSOPHILA-LEBANONENSIS DETERMINED BY IN-SITU HYBRIDIZATION

One modification of the primitive karyotype of the Drosophilidae is th e absence of dot chromosomes. The origin of this modification is diver se. In some cases, the fate of the dot chromosomes can be directly inf erred from cytogenetic analysis but in other cases a genetic or a comb ined molecular and cytogenetic analysis is needed, as occurs in Drosop hila willistoni and Scaptodrosophila lebanonensis. We determined the l ocation of four dot chromosome sequences in D. willistoni and S. leban onensis using in situ hybridization. Drosophila melanogaster and D. vi rilis, which possess dot chromosomes, were used as a control. The in s itu hybridization results show that dot chromosome genes of D. melanog aster and D. virilis are closely linked in chromosome 3 of D. willisto ni and in chromosome X of S. lebanonensis. These results suggest an au tosome-dot fusion in D. willistoni and an X-dot fusion in S. lebanonen sis, two different paths in the evolution of dot chromosomes.