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The Biological Bulletin, Vol 183, Issue 3 387-393, Copyright © 1992 by Marine Biological Laboratory

DEVELOPMENT AND REPRODUCTION

Genetic Consequences of Blocking Polar Body I with Cytochalasin B in Fertilized Eggs of the Pacific Oyster, Crassostrea gigas: II. Segregation of Chromosomes

X. Guo, W. K. Hershberger, K. Cooper and K. K. Chew
School of Fisheries, WH-10, University of Washington, Seattle, Washington 98195

The effect of blocking polar body I (PB1) with cytochalasin B (CB) on subsequent chromosome segregation was studied in fertilized eggs of the Pacific oyster, Crassostrea gigas. To block the release of PB1, fertilized eggs were treated with CB (1.0 {mu}g/ml) for 15 min beginning at 5 min post-fertilization at 25{deg}C. Chromosome segregation in both control and CB-treated eggs was analyzed with an acetic orcein stain. In untreated eggs, ten maternal tetrad chromosomes went through meiosis I and II, and released two polar bodies, reaching a haploid number of 10 chromatids. In CB-treated eggs, meiosis I proceeded normally and produced two groups of dyads, ten in each group. However, blocking PB1 dramatically changed chromosome segregation in meiosis II. In the majority of the treated eggs (68%), the two groups of dyads from meiosis I entered meiosis II through a "tripolar segregation", although two other types of segregation, namely "united bipolar" (7%) and "separated bipolar" (12%) were also observed. After anaphase II, chromatids at the peripheral pole were released as polar body II (PB2). The release of two sets of chromatids as PB2 through either a united bipolar or a separated bipolar segregation resulted in the formation of meiosis I triploids (14%). The release of one set of chromatids as PB2 from an unmixed tripolar or a separated bipolar segregation formed meiosis I tetraploids (20%). Aneuploids (56%) were produced, primarily when the two groups of dyads from meiosis I united or overlapped before entering the tripolar segregation.


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P. L. Hertzler
Twin Meiosis 2 Spindles Form After Suppression of Polar Body 1 Formation in Oocytes of the Marine Shrimp Sicyonia ingentis
Biol. Bull., April 1, 2002; 202(2): 100 - 103.
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Copyright © 1992 by the Marine Biological Laboratory.