However, differences in the number of univalents
outside the equatorial plate in Metaphase I were found between Don Rene and FA-L2 (Fig.
Each homologue chromosome is oriented parallel to the achromatic spindle, thus the telomeric regions are active in meiosis I, while the X chromosome is observed as univalent
Hybrids between species with widely divergent chromosome counts typically exhibit a greater proportion of univalents
, trivalents and other irregular meiotic chromosome associations than hybrids between species with similar numbers of chromosomes (Faulkner, 1973; Schmid, 1982; Cayouette & Morisset, 1985; Whitkus, 1988; Cayouette and Catling 1992; Luceno, 1994).
There was, however, a general trend toward an increased number of univalents
per cell as aneuploid numbers increased.
Apart from the tedium of this method, the best and most simple proof of alloploidy is the occurence of 3n univalents
in crosses with different diploids with known genomic constitution: "Auf diesen Wegen kann der Genomanalytiker innerhalb einer Allopolyploidie aufweisenden Gattung oder, wenn wir die Gattungsgrenzen des Systematikers uberschreiten, innerhalb einer alloploide Beziehungen aufweisenden Artsgruppe ihren 'Genomschatz' feststellen" (Kihara, 1930: 267).
Trivalents were clearly the predominant form of synapsed chromosomes in eggs from triploid Pacific oysters, although incomplete synapsis was frequent with a mixture of tri-, bi-, and univalents
Another 18% of the metaphase I cells contained two univalents
and 13 bivalents (Fig.
Support for that inevitable conclusion was provided in one 2 n = 14 M Tradescantia commelinoides individual with abnormally low chiasma frequency which frequently formed one and rarely two ring univalents
typical of internal pairing of chromosomes of that type.
At metaphase I, univalents
were less common in the hybrids than in the parents.
Both Frio and PI 409704 are pentaploids with 45 chromosomes that associate essentially as 18 bivalents and 9 univalents
during metaphase I of meiosis.
The translocation event most likely originated from simultaneous misdivision of univalents
and subsequent joining of the wheat chromosome 4B short arm with the homoeologous Lophopyrum chromosome arm.
1] plants carrying 25 bivalents and two univalents