Chromosomal basis of dosage compensation in Drosophila. V. Puffwise analysis of gene activity in the X-chromosome of male and female Drosophila hydei.

Abstract

A critical analysis of the puffing activity and transcribing activity patterns of different sites of the X-chromosome of the male and female larval salivary glands of Drosophila hydei has been presented. The results show that within the limitations of the resolving power of the technique and variability inherent in the general chromosomal conditions the puffing activities of the different sites of the X-chromosome are very much alike in the two sexes. Of the 15 puffing sites in the X-chromosome, most of the sites either show good concordance in the two sexes or resemble in their highest class value. Only 4 sites (4CD, 8A, 16C and 20B) show considerable discordance in the activity pattern between male and female. Incorporation of 3H-uridine in the X-chromosome also reveals that there is indeed a reasonable degree of superimposition of the number of silver grains in the X-chromosomal puffs of the two sexes. Whatever disparity that exists between the grain numbers in the two sexes can be explained on the basis of sister-class compensation. These results have been interpreted as evidence in support of the piece-meal mechanism of dosage compensation in Drosophila, operating through hyperactivation in the male.