Electron microscopic band-interband pattern of polytene chromosomes in Drosophila nasuta albomicans. 2. Salivary gland chromosome 2L.

The band-interband pattern (division 28-52) of salivary gland chromosome 2L in Drosophila nasuta albomicans was studied by light (LM) and electron microscopy (EM) using squash preparations and surface-spread polytene (SSP) chromosome preparations, respectively. LM and EM maps were complied. Based on the digitized EM patterns of five homologous SSP chromosomes a computerized EM chromosome map was plotted. The EM pattern analysis showed a total number of 479 chromosome bands with an almost 83% increase compared with the LM analysis of squash preparations. By extrapolation of the data from 39% of the polytene genome analysed so far in D. n. albomicans, a total number of 2,926 chromosome bands was calculated. This is almost the same number of bands as was calculated earlier for Drosophila hydei using the same SSP chromosome preparation technique. The data in the literature concerning variations in the number of chromosome bands in different Drosophila species, the various chromosome preparation techniques adopted, and the different criteria used for the EM pattern analyses, are discussed.