Struktur-Differenzierungen im Y-Chromosom von Drosophila hydei und ihre Beziehungen zu Gen-Aktivitäten

Summary

During the growth stage of the primary spermatocytes of Drosophila hydei intranuclear structures can be seen, which are comparable to the loops of lampbrush chromosomes. These structures are formed by specific organizers. Sequence and loci of these organizers on the Y chromosome have been mapped by cytogenetic methods, using Y translocations and Y fragments. For the localization analysis the long arm of the Y chromosome is divided into ten equal segments which are designated 1–10 starting at the kinetochore. The organizer of the loop called “threads” is located in segment 10 or 9 at the distal tip of the long arm, the chromosome site which forms the “pseudonucleolus” is located in segment 9 or 8, the locus of the site for the “tubular ribbons” was determined in segment 2 or 3 and that for the “clubs” in segment 1. A new, fifth loop of the Y chromosome has been detected. It has been called “noose” and its organizer lies on the short arm of the Y chromosome. Large parts of the Y chromosome, including one segment which is more than one half of the long arm are not involved in loop-formation. If Y chromosome segments containing any one of the five loops are lacking, the males are always sterile. Furthermore, spermiogenesis is blocked at different stages depending upon which of the loops is absent. The possible role of the genetic information located within the loops is discussed.