Figure 1

Chromosome structure of Drosophila melanogaster. The left and right arms of chromosomes 2 (2L, 2R) and 3 (3L, 3R), the small chromosome 4, and the sex chromosomes X and Y are shown (adapted from [12]). The numbers correspond to lengths in megabases. The euchromatic portions of the chromosome arms (white) correspond to the Release 3 euchromatic sequence described in Celniker et al. [47]. The lengths of the heterochromatic portions of the chromosome arms (green) are estimated from measurements of mitotic chromosomes [76]. The length of the heterochromatin on the X chromosome is polymorphic among strains and can comprise from one-third to one-half of the length of the mitotic chromosome. Our cytogenetic experiments show that Release 3 euchromatic sequence (white) extends into the centric heterochromatin by approximately 2.1 Mb (see Results).