MOLECULAR AND CYTOGENETICAL CHARACTERIZATION OF THE 10A1-2 BAND AND ADJOINING REGION IN THE DROSOPHILA-MELANOGASTER POLYTENE X-CHROMOSOME

Some 300 kb of DNA from the 9F12-10A7 X chromosome region (seven bands ) uncovered by Df(1)v(L3) were cloned and 31 break points of chromosom e rearrangements within the region were mapped. Positions of 12 genes found earlier in genetic saturation experiments, transcripts and P ele ment-induced mutations were located on the physical map using either c hromosome rearrangements or Southern blot hybridizations. Data on the position of the break points, genes and polytene chromosome bands allo w the following conclusions to be made. (1) The size of the bands in t he region varies between 4 kb (10A6 and 7) and 183-195 kb (10A1-2). Th e compaction ratio of DNA in bands varies from 8-36 (10A6 + 7) to 151- 161 (10A1-2). Therefore, fine and thick bands appear to have different kinds of DNP packaging. (2) The bands differ in genetic content. Fine bands contain from one to three genes. In contrast, the 10A1-2 band c ontains three genes and at least six transcribed DNA fragments. (3) Co mparison of genetic and physical maps shows that in this region 0.01 c entiMorgan corresponds to 3.3 kb of DNA.