Gene transfer in Drosophila melanogaster: cytological alterations in the salivary chromosomes of transformed stocks

Abstract

Cytological abnormalities are observed in salivary chromosomes of stocks of Drosophila melanogaster possessing DNA-induced, v ⁺ transformations mapping either at 1∓0.0 or 1∓33.0. In initial studies, the untransformed control stock and six transformed stocks were assigned code numbers prior to cytological examination. Salivary chromosome regions 1B9 · 10—1C2 · 3 and 10A1 · 2—10B1 · 2 were carefully examined in each of the coded stocks. (Band 1B11 is tentatively identified as the site of the suppressor-of-sable locus at 1∓0.0 and band 10A1 is the site of the vermilion locus at 1∓33.0.) When cytological studies were complete each of the stocks was identified. In every transformed stock examined, anomalies had been scored in association with the chromosome region corresponding to the map position of the DNA-induced alteration. In the control stock, anomalies were observed at neither position. — Approximately 10–15% of the nuclei in transformed stocks exhibit significant departure from normality in the pertinent chromosome region. The perturbations range from minor alterations of banding pattern to apparent pieces of extra chromatin in the most extreme cases. In stocks with v⁺ transformations mapping at 1∓33.0, apparent extra chromatin is observed with frequencies varying from 0.05 to 0.02. In these cases the abnormal structures are associated with salivary band 10A1 · 2, forming a band-like structure, frequently an almost perfect doublet (open or closed), often lying in an abnormal position, and with fine chromatin threads connecting to the chromosomal doublet. In stocks with v⁺ transformations mapping at 1∓0.0, apparent extra chromatin is observed with a frequency of about 0.001. These abnormal structures are frequently thread-like, lying to the side or off the tip of the chromosome, with compact regions which sometimes resemble chromomeres, and with fine threads connecting to the chromosomal 1B11 region.