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The Meiotic Loss of Unpaired Chromosomes in Drosophila Melanogaster



The Meiotic Loss of Unpaired Chromosomes in Drosophila Melanogaster



Genetics 39(3): 365-377



Four different types of XY and XYY males of Drosophila melanogaster were tested for loss of their X and Y chromosomes. The types differed in the amount and distribution of heterochromatin carried on the X chromosome. The evidence indicates that loss of these chromosomes occurs only in those cases in which the homology between them is very much reduced, indicating that chromosome loss occurs predominantly when the chromosomes are unpaired. The frequencies of loss for those chromosomes which showed loss are as follows: (1) the Y chromosome in an XY male, 42%; (2) the X chromosome in an XY male, 0.3% (not significantly different from 0); (3) the X chromosome in an XYY male, 53%; (4) one of the Y chromosomes in an XYY male, 24%. Tests were also run to determine the frequency of loss of a Y chromosome and a Y chromosome fragment in XXY (and Y fragment) females. The frequency of loss in both of these cases was 25%. These frequencies, which represent the total loss of the chromosome, must be minimum estimates of the loss of the unpaired chromosome. The attached XY chromosome is lost with a frequency that varies from 11% to 24%. The application of this loss to previously published data on the tandem metacentric compound X chromosome is discussed in detail. The data are in accord with the idea that primary non- disjunction in the female results from occasional failure of the X chromosomes to pair, with the consequent loss of one or both of these resulting in the observed discrepancy between the recovery of primary exceptional males as compared with primary exceptional females. From the data taken as a whole, and particularly from evidence indicating that the attached X chromosome is not lost in the absence of a homolog, it is suggested that normal disjunction is dependent upon the pairing of heterochromatic regions and is independent of pairing at the centromere region.

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Accession: 025853167

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PMID: 17247490


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