The role of genetic balance in control of transcription rate in the X-chromosomes of Drosophila melanogaster

The intensity of transcription in the polytene X-chromosome of the salivary glands of Drosophila melanogaster has been determined as a function of the ratio of X-chromosomes to autosomes (X:A). Autoradiographic measurements revealed that the single X-chromosome in males (1X2A) incorporates twice as much label as each of the two X-chromosomes in females (2X2A) which confirms the earlier report of Mukherjee and Beermann (1965). The addition of the third autosome set in super-males (1X3A) does not result in an increase of RNA synthesis in the X-chromosomes as compared to normal males (1X2A). In superfemales (3X2A) carrying an extra X-chromosome the transcription in each of the X-chromosomes proceeds with the same rate as in diploid (2X2A) or triploid (3X3A) females. In intersexes (2X3A) the rate of transcription in each of X-chromosomes is intermediate between male and female levels. — The comparison of transcription rates in X-chromosomes with the levels of two enzymes coded for by sex-linked genes in males, females, super-females and intersexes (Faizullin and Gvozdev, 1972, 1973) revealed that the dosage compensation of the enzyme synthesis is effected at the level of transcription.