Some of the DNA is packaged into a giant chromosome, and some is contained within small packages known as plasmids.

The mature larvae show giant chromosomes in the salivary glands called polytene chromosomes-"puffs" indicate regions of transcription and hence gene activity.

Giant chromosomes in the lampbrush form are useful model for studying chromosome organization, genome function and gene expression during meiotic prophase, since they allow the individual transcription units to be visualized.

In particular, Dr. Pavan introduced into biology the cytogenetical study of Rhynchosciara angelae, a fly which is noted for its giant chromosomes, thus facilitating the determination of the loci of genes.