Masters Theses

Date of Award

5-1994

Degree Type

Thesis

Degree Name

Master of Science

Major

Zoology

Major Professor

Bruce D. McKee

Committee Members

Mary Ann Handel, Ranjan Ganguly

Abstract

Homologous chromosome pairing is essential for the subsequent events in meiosis.. Pairing, in most organisms, leads to recombination, in which chiasmata are formed and hold the chromosomes together until segregation at Anaphase I. This is not so in Drosophila melanogaster males, where there is no recombination or chiasma formation, but there is pairing of the homologs. Therefore, it is important to locate where pairing occurs in order to understand how homologous chromosomes pair. It is known that in Drosophila the autosomes pair in the euchromatin and that the sex chromosomes pair in the heterochromatin. The pairing of the X and Y is mediated by ribosomal DNAs (rDNAS) which are located near the base of the short arm of the Y and in the centric heterochromatic region of the X. A single, complete copy of an rDNA repeat has been shown to stimulate pairing of the sex chromosomes when located on a heterochromatically deficient X chromosome. Also, insertions of the 5 half of the rDNA which includes all of the external transcribed spacer (ETS) region, part of 18s gene, and a part or all of the promoter region, have been shown to restore pairing. Three X-linked transformation stocks have been found, each transformed with the same transformation vector, which includes only 180bp of the promoter region and the entire intergenic spacer. These three transformed stocks have different X-Y pairing abilities.The present study was undertaken to ascertain the basis for the differences in their pairing abilities. In situ hybridization to polytene chromosomes in the salivary glands of the larvae in each of the stocks was done to locate the insertion site. Two of the stocks have an insertion site at the tip of the X and one stock has the insertion site at 14D of the X. Also, genomic Southern blot anaylsis and cloning of the rDNA fragment were done to determine the structure of the rDNA insert to understand why there is such a difference in the pairing ability of each of these stocks. Southern blot analysis revealed that there was a size difference among the three stocks. From cloning, it was shown that the difference lies within a repetitive region of the intergenic spacer.

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