Gene-centromere mapping of 312 loci in pink salmon by half-tetrad analysis

We estimated recombination rates between 312 loci and their centromeres in gynogenetic diploid pink salmon (Oncorhynchus gorbuscha) that we produced by initiating development with irradiated sperm and blocking the maternal second meiotic division. Amplified fragment length polymorphisms (AFLPs) were significantly more centromeric than loci identified by three other techniques (allozymes, microsatellites, and PCR using primer sequences from interspersed nuclear elements). The near absence of AFLPs in distal regions could limit their utility in constructing linkage maps. A large proportion of loci had frequency of second division segregation (y) values approaching 1.0, indicating near complete crossover interference on many chromosome arms. As predicted from models of chromosomal evolution in salmonids based upon results with allozyme loci, all duplicated microsatellite loci that shared alleles (isoloci) had y values of nearly 1.0.Key words: meiosis, AFLP, microsatellites, isoloci, Oncorhynchus gorbuscha.

Sexual reproduction in the Peronosporomycetes (chromistan fungi)

An overview of sexual reproduction in the Peronosporomycetes leads to the recognition of constant features and variable traits. Variation in characters is accorded different weighting depending on its use for taxonomic identification or phylogenetic systematics. The phylogenetic significance of features of gametangial morphogenesis, such as vacuolation and the patterns of nuclear meioses and abortions, can be related to morphological characters such as the persistence of periplasm and oogonial and oospore wall deposition. The cellular reorganization occurring in the oogonium and oospores, particularly in relation to the possible functions of the dense body vesicle system and the glucan, phosphate, and lipid oospore reserves, may be critical for the internal morphology of the mature oospore and its function. Such differences are valuable for morphometric analysis, which lends itself to new identification procedures. The ecological implications of these differences in the production of oogonia and oospores are considered; sexual reproduction (its frequency or absence) may be crucial for successful life-history strategies in biodiversity. Key words: meiosis, karyogamy, syngamy, morphogenesis, morphometry, wall membranes.

Meiotic behavior of a tiny fragment chromosome that carries a transposed centromere

A supernumerary, tiny chromosome with a transposed centromere, in an apparently normal maize background, was observed through meiotic stages from pachytene through anaphase II. Departures from normal meiotic chromosome behavior were noted for this tiny chromosome. These included failure of the usual degree of condensation at pachytene, failure of synapsis, and most strikingly the ability of sister centromeres to interact with the spindle on schedule with the normal dyads at anaphase I, so that monads were commonly distributed to the poles for telophase I and then often lagged at anaphase II. Possible significance of the unusual behavior is discussed. Key words: meiosis, fragment, centromere.

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

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 Key words: meiosis, multivalents, orientation, workshop.

Persisting demibivalents: a unique meiotic behaviour in Cuscuta babylonica Choisy

Idiosyncratic chromosome behaviour during meiosis was found in pollen mother cells of Cuscuta babylonica Choisy, a thread-like holoparasitic herb. Its main features are among the following: (i) telomeric association between homologues through most stages of the process, which leads to persisting chromatid bivalents (= "demibivalents"); (ii) uncommon chromosome segregation in first and second anaphase; and (iii) prolonged intensified heterochromatinization. Although "regular" in its own way, this process leads to the formation of unviable products. Its further investigation might contribute to our understanding of the role of the spindle and chromosome movement in the ordinary process of meiosis. Key words: meiosis (abnormal), persisting demibivalents, Cuscuta babylonica.