Meiosis in Saccharomyces cerevisiae proceeds principally in the same manner as in other Ascomycetes. Leptotene is characterized by unpaired lateral components and pachytene by the presence of extensive synaptonemal complexes. The synaptonemal complex has the same dimensions and is similar in structure to those described for other organisms. Chromosome counts can now be made by reconstructing the synaptonemal complexes. Diplotene nuclei consistently contain a single polycomplex. The behaviour, doubling and the fine structure of the spindle plaque provide additional markers for the different stages of meiosis.

EGELMITANI, M., OLSON, L.W. and EGEL, R. 1982. Meiosis in Aspergillus nidufans: Another example for lacking synaptonemal complexes in the absence of crossover interference. -Hereditas 97: 179-187. Lund, Sweden. ISSN 0018-0661. Received January 28, 1982 Immature cleistothecia of Aspergillus nidulans (mutant bi, dcl) were serial-sectioned and studied by electron microscopy. Synaptonemal complexes or other conspicuous signs of chromosomal pairing were not observed in this material. This deviation from most other eukaryotes may be of significance for explaining the likewise unusual absence of crossover interference in this organism, as well as in Schizosaccharomyces pombe. In addition, we report on division spindles and spore formation in A . nidulans. Literature cited ANDERSON, P. J . 1967. Purification and quantitation of glutaraldehyde and its effect on several enzyme activities in skeletal muscle. -J . Histochem. Cytochem. I S : 652-661 BARRET, J . M., HEIDIGER, P . M. and KENNEDY, S. W. 1976. Chelated bismuth as a stain in electron microscopy. -J . Histochem. Cytochem. 23: 780-783 York. p. 447-510 DALTON, A. J. 1955. A chrome-osmium fixative for electron microscopy. -Anat. Rec. 121: 281 EGEL, R. 1978. Synaptonemal complex and crossing-over: structural support or interference? -Heredity 41: 233-237 GALEY, F. R. and NILSSON, S. E. G. 1966. A new method for transferring sections from the liquid surface of the trough through staining solutions to the supporting film of a grid. -J . Ultrastruct. Res. 14: 405-410 HOLM, P. B . and RASMUSSEN, S. W. 1980. Chromosome pairing, recombination nodules and chiasma formation in diploid Bombyx males. -Carlsberg Res. Commun. 45: 483-548 HOLM, P. €3.. RASMUSSEN, S. W., ZICKLER, D., LU, B . C and SAGE, J. 1981. Chromosome pairing, recombination nodules and chiasma formation in the basidiomycete Coprinus cinereus. -Carlsberg R e s . Commun. 46: 305-346 JONES, G . H . 1967. The control of chiasma distribution in rye. -Chromosoma 22: 69-90 melanogaster. -Geneticu 55: 47-49 SIMCHEN, G., KASSIR, Y., HORESH-CABILLY, 0. and FRIEDMANN, A. 1981. Elevated recombination and pairing structures during meiotic arrest in yeast of the nuclear division mutant cdc5. -M u / . Gen. Genet. 184: 46-51 SNOW, R. 1979. Maximum likelihood estimation of linkage and interference from tetrad data. -Genetics 92: 231-245 SPURR, A. R . 1969. A low-viscosity resin embedding medium for electron microscopy, -J . Ultrastruct. R e s . 26: 31-43 , L. W. 1975. The synaptonemal complex and the spindle plaque during meiosis in yeast. -Chromosorna 50: 1-23 ZONNEVELD, B.J.M. 1974. a -1,3 glucan synthesis correlated with a -1,3 glucanase synthesis, conidiation and fructification in morphogenetic mutants of Aspergillus nidulans. -J . Gen. Microbiol. 81: 445-451 ZONNEVELD, 9. J . M. 1975. Sexual differentiation in Aspergillus nidulans 1. The requirement for manganese and its effect on a -1,3 glucan synthesis and degradation. -Arch. Microbiol. 105: 101-104

Meiotic prophase has been studied by both light and electron microscopy in diploid cell lines (h+/h‐) of Schizosaccharomyces pombe. One wild‐type and one mutant strain were used, the latter (mei4‐B2) being blocked after premeiotic DNA synthesis and after commitment to meiosis. Meiosis and sporulation were induced in liquid culture by a shift to a sporulation medium devoid of a nitrogen source. The time course was determined from light‐microscopic preparations; most cells passing through meiotic prophase between 5 and 8 h after the shift. In samples from that interval, ca. 20% of the nuclei were elongate in shape, containing strands of chromatin in rough alignement with the long axis of the nucleus. This stage was found to accumulate in the mutant. A bundle of microtubules, just outside of the spindle plaque, apparently stabilized the elongated shape of the nuclei. Linear electron‐dense structures were observed to populate these nuclei. They resembled unpaired lateral elements of synaptonemal complexes in other organisms. Yet, at no times did we observe a tripartite complex or any other sign of chromosomal pairing in our material.

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