Some consequences of spermatogonial exchange in long inversions of the X chromosome of Drosophila melanogaster.

by Lindsley, Dan L.

Abstract (Summary)
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Among the progeny of males carrying the inverted I chromosome, [...], individuals are found which have lost the terminal euchromatic segment of the inversion. This has been interpreted in the past (Sidorov 1940, 1941) as the result of exchange between the distal heterochromatin of the inversion and the short arm of the Y chromosome, and, indeed, the reciprocal recombinant type may be recovered, i. e. a Y with its short arm replaced by the terminal euchromatin of [...]. The fact that such derivatives occur in clusters and represent recombination which has occurred in males indicate that the events in question are mitotic rather than meiotic in origin. An analysis of 44 such recombinant X chromosomes recovered from 273,721 offspring of males carrying the distal heterochromatin of [...] reveals that previous notions represent an oversimplification of the actual case. When the chromosome carries large heterochromatic segments at its base, the distal heterochromatin many tend to pair with its own base in preference to pairing with the Y. Such pairing may occur in either direction, i.e., eucentrically or dyscentrically, as may pairing between the X and Y. Reversal of ordinary pairing relationships may result in the formation of dicentric bridges, and the evidence indicates that such bridges break at anaphase. It has been possible to demonstrate exchange between the distal heterochromatin of [...] and all other sex linked heterochromatic blocks except [...], and indications are that this event may not occur. No evidence has been found favoring any sort of fusion circle subsequent to bridge breakage, but the experimental arrangement favored detection of only a chromatid and not a chromosome type of cycle.
Bibliographical Information:

Advisor:Alfred Henry Sturtevant

School:California Institute of Technology

School Location:USA - California

Source Type:Master's Thesis



Date of Publication:01/01/1952

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