One of the rewards of having a Drosophila melanogaster whole-genome sequenc
e will be the potential to understand the molecular bases for structural fe
atures of chromosomes that have been a Long-standing puzzle. Analysis of 2.
6 megabases of sequence from the tip of the X chromosome of Drosophila iden
tifies 273 genes. Cloned DNAs from the characteristic bulbous structure at
the tip of the X chromosome in the region of the broad complex display an u
nusual pattern of in situ hybridization. Sequence analysis revealed that th
is region comprises 154 kilobases of DNA flanked by 1.2-kilobases of invert
ed repeats, each composed of a 350-base pair satellite related element. Thu
s, some aspects of chromosome structure appear to be revealed directly with
in the DNA sequence itself.