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The detection of mosaics and polyploids in a hereditary mosaic strain of the silk moth, Bombyx mori, using egg colour mutants

Published online by Cambridge University Press:  14 April 2009

Hiroyasu Ebinuma*
Affiliation:
Laboratory of Sericultural Science, Faculty of Agriculture, University of Tokyo, Bunkyo-ku, Tokyo, 113 Japan
Masahiko Kobayashi
Affiliation:
Laboratory of Sericultural Science, Faculty of Agriculture, University of Tokyo, Bunkyo-ku, Tokyo, 113 Japan
Jun Kobayashi
Affiliation:
Laboratory of Sericultural Science, Faculty of Agriculture, University of Tokyo, Bunkyo-ku, Tokyo, 113 Japan
Toru Shimada
Affiliation:
Laboratory of Sericultural Science, Faculty of Agriculture, University of Tokyo, Bunkyo-ku, Tokyo, 113 Japan
Narumi Yoshitake
Affiliation:
Laboratory of Sericultural Science, Faculty of Agriculture, University of Tokyo, Bunkyo-ku, Tokyo, 113 Japan
*
* Corresponding author.
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Summary

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To analyze abnormal fertilization in a hereditary mosaic strain (mo/mo) of Bombyx mori, the percentages of diploidy mosaic, polyploidy mosaic and polyploid eggs in a batch were estimated by using egg colour mutants (pe re). Among 48 890 eggs from crosses of pe + / + re, mo/mo females with pe re/pe re males, 9409 abnormal eggs were obtained; 4472 of them were diploidy mosaics (red-white eggs), 4038 were polyploids (black eggs) and 899 were polyploidy mosaics (566 black-white, 256 black-red and 77 black-white-red eggs). The total number of diploidy mosaic eggs was approximately equal to that of polyploid eggs. A significant correlation was detected between the diploidy mosaic and polyploid egg ratios within a batch. This suggests that diploidy mosaics are produced by double fertilization in which two genetically non-identical egg nuclei are fertilized in turn by a sperm, and polyploids are formed by the fertilization of a diploid, non-disjunctive egg nucleus gamete by a single sperm. Our results also indicated the presence of common factors modifying both mosaic and polyploid frequency. The concordance of the observed ratio of polyploidy mosaic eggs (1·84%) with the expected value (diploidy mosaic ratio × polyploidy ratio × 2 = 1·83%) suggests that the formation of mosaics occurs independently of the formation of polyploids in this abnormal fertilization process. We point out that it is necessary to modify Goldschmidt & Katsuki's general model to explain abnormal fertilization, and we propose several possible models.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1988

References

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