ARTICLE

CHROMOSOMAL BASIS OF DOSAGE COMPENSATION IN DROSOPHILA : III. Early Completion of Replication by the Polytene X-Chromosome in Male: Further Evidence and Its Implications

S. C. Lakhotia ¹ and A. S. Mukherjee ¹

¹ From the Cytogenetics Laboratory, Department of Zoology, University of Calcutta, Calcutta, India

Thymidine-³H labeling patterns on the X (section 1 A to 12 E of Bridges' map) and 2 R (section 56 F to 60 F of Bridges' map) segments in the salivary gland chromosomes of Drosophila melanogaster have been analyzed in male and female separately. The observed patterns fit, with a few exceptions, in a continuous to discontinuous labeling sequence. In nuclei with similar labeling patterns on the 2R segment in both sexes, the number of labeled sites on the X in male is always less than in female X's. The labeling frequency of the different sites on the male X is considerably lower than those on the female X's, while the sites on the 2R segment have very similar frequency in the two sexes. The rate of thymidine-³H incorporation (as judged by visual grain counting) is relatively higher in male X than in female X's. It is concluded that the model sequence of replication in polytene chromosomes follows a continuous to discontinuous labeling sequence, and that the single X in male completes its replication earlier than either the autosomes in male or the X's in female. This asynchronous and faster rate of replication by the polytene X-chromosome in male substantiates the hypothesis of hyperactivity of the single X in male as the chromosomal basis of dosage compensation in Drosophila.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

• Rudkin, G. T., Tartof, K. D. (1974). Repetitive DNA in Polytene Chromosomes of Drosophila melanogaster. Cold Spring Harb Symp Quant Biol 38: 397-403 [Abstract]  

Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents