Chromomeres and puffing in experimentally induced polytene chromosomes of Calliphora erythrocephala.

In the most advanced types of meroistic ovaries the synthesis of RNA for the growing oocyte in each follicle is taken over by nurse cells, i.e., sister cells of the definite egg cell. In calliphora, the highly polyploid nurse cells (NC) develop a polytene karyotype under conditions of strict brother-sister inbreeding and using a controlled selection technique. A comparison of the polytene NC-chromosomes with those from the pupal bristle forming cells reveals an unexpected discrepancy: while both chromosome complements exhibit a constant banding pattern it is not possible to homologize the two tissue specific patterns by identifying homologous band-sequences. Puffing in NC likewise turns out to be unusual in its extent as well as in that is remains constant during long periods of oogenesis. In a more detailed discussion an interpretation and evaluation of these findings will be attempted.