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Medientyp:
E-Artikel
Titel:
Crossing-Over, Fragmentation, and Formation of New Chromosomes in an Allium Species Hybrid
Beteiligte:
Emsweller, S. L.;
Jones, H. A.
Erschienen:
The University of Chicago Press, 1938
Erschienen in:Botanical Gazette
Sprache:
Englisch
ISSN:
0006-8071
Entstehung:
Anmerkungen:
Beschreibung:
<p>1. The hybrid between A. cepa and A. fistulosum is unusual because of the high frequency of complete pairing, fragmentation, and formation of chromatin bridges. 2. Fragments were found as early as late pachytene, increasing in frequency to first telophase, then dropping. Their origin is explained as a result of unusual crossing-over. The decrease in number is probably due to an actual loss. Their possible digestion in the cytoplasm by enzymes is suggested as an explanation for this. 3. Chromatin bridges were found at first and second anaphases and telophases. It is suggested that these bridges probably arise from unusual crossing-over, some in inverted sectors, but to a considerable extent because of positional effect of insertion regions or homologous sectors. The cytological evidence also points to some interpretation other than breakage as an explanation of their dissolution. From the behavior of these bridges it was inferred that some reach the microspores, depending on the chance orientation of their two insertion regions. In the microspore mitosis they will form an X configuration when the insertion regions of one chromatid are oriented to opposite poles. This was confirmed cytologically on a slide from Rhoeo discolor kindly lent us by Dr. Dermen of this Division. 4. The presence of morphologically new chromosomes was determined in the first division of hybrid microspores. These were undoubtedly formed by crossing-over between the two genoms.</p>