This is a photo of a set of Drosophila salivary gland polytene chromosomes. The five major chromosome arms (X, 2L, 2R, 3L, and 3R) are labeled in red at their telomeres, as is the small chromosome 4. The arms extend out from the chromocenter, which contains the centromeres and the condensed pericentric heterochromatin in which they are embedded. This photo was ripped off from Tom Kaufman at Indiana University, then digitally altered to make it even prettier.
Many of the genes we currently study are indicated. Click on them to learn more.