The orientation of multivalents at meiotic metaphase I: a workshop report

Abstract

SYBENGA, J., and RICKARDS, G. K. 1987. The orientation of multivalents at meiotic metaphase I: a workshop report.Genome, 29: 6 12-620. During a workshop with 13 participants, several aspects of multivalent orientation at meiotic (pro)metaphase were discussed in an attempt to resolve some of the most prominent controversies with respect to terminology, interpretation of observations, and the validity of hypotheses and theories. For several terms and concepts, descriptive definitions were formulated that are recommended for general use. In the analysis of the behaviour of the multivalent in meiosis preprometaphase shape and position as important factors in final orientation were discussed, as well as the first contact between spindle and kinetochores and the role of reorientation. Specific characteristics of different multivalents and expected frequencies of different orientation types were considered. Finally, a few remarks on data collection and analytical procedures were made

Multivalents resulting from monobrachial homologies within a hybrid zone in Dichroplus pratensis (Acrididae): meiotic orientation and segregation

“…Further reorientation probably occurs at late MI, since almost invariably, abnormal second spermatocytes exist at frequencies lower than those of abnormal first metaphases. The discrepancy between MI orientation and AT segregation could be also due to the analysis of different cell populations (Sybenga & Rickards, 1987). In D. pratensis, however, it is evident that, despite the multivalent and male involved, abnormal second spermatocytes are almost invariably less than expected from non-alternate MI orientation, which also occurs in trivalents of this species .…”

“…(e) (f) 222 C. J. BIDAU this configuration has been variously termed V-orientation (Rickards, 1983), convergent (John & Lewis, 1963;, disjunctional (John, 1983) and alternate (Rickards, 1983;Sybenga & Rickards, 1987). For clarity, the more usual term 'alternate' will be used in this paper to describe chain multivalents disjunctionally oriented, and 'non-alternate' for all those orientations that do not ensure balanced segregation.…”

“…Orientation and segregation of multivalents have been the subjects of many experimental and theoretical investigations, although controversies still persist (John, 1987;Sybenga & Rickards, 1987). In addition, the role of monobrachial homologies in the establishment of postzygotic reproductive isolation and evolutionary divergence, is the subject of speculation, discussion and model-making (Capanna, 1982;Capanna et al, 1985;Baker & Bickham, 1986;Searle, 1986aSearle, , 1988Sites & Moritz, 1987;Bidau, 1988Bidau, , 1990Redi & Capanna, 1988).…”

Proximal chiasmata induce non-disjunctional orientation of Robertsonian trivalents in a grasshopper

“…Many works on plants and animals have been devoted to the study of factors that affect and modify the meiotic behaviour of structural rearrangements (Sybenga, 1975;Rickards, 1977;1983;Wise & Rickards, 1977;John, 1987;Sybenga & Rickards, 1987;Bidau & Mirol, 1988). Their potential ability to produce negative heterosis through imbalanced segregation is their principal quality relative to speciation (King, 1987).…”

“…In the case of translocation (Robertsonjan or reciprocal) heterozygotes such behaviour is ruled by factors such as inter-centromere distance, size of the involved chromosomes, the initial position of the configuration in the meiotic cell, the premeiotic disposition of chromosomes, the relative time of centromere activation, the number and position of chiasmata and the genetic background (Rickards, 1983;Narasinga Rao & Sybenga, 1984;Arundhati et al, 1986;John, 1987;Sybenga & Rickards, 1987). These factors, jointly with selective and stochastic processes, are responsible for the fate of a given chromosomal rearrangement in a natural population.…”