Over 200 mutants that affect sexual development have been isolated and analysed in Neurospora crassa. Mutational, recombinational, molecular analyses on the mating type region show genes A a specify both function vegetative (heterokaryon) incompatibility function. The two functions are inseparable by recombination but separable mutational event, as am33. An unlinked tol mutation suppresses associated with without affecting their Mating (except am33), well male- female-sterile mutants,...

A gene unpaired during the meiotic homolog pairing stage in Neurospora generates a sequence-specific signal that silences expression of all copies gene. This process is called Meiotic Silencing by Unpaired DNA (MSUD). Previously, we have shown SAD-1, an RNA-directed RNA polymerase (RdRP), required for MSUD. We isolated second involved this process, sad-2 . Mutated Sad-2 RIP alleles, like those Sad-1 , are dominant and suppress Crosses homozygous blocked at prophase. SAD-2 colocalizes with...

Abstract Meiosis and ascospore development in the four‐spored pseudohomothallic ascomycetes Neurospora tetrasperma, Gelasinospora Podospora anserina, P. fefraspora have been reexamined, highlighting differences that reflect independent origins of condition different genera. In these species, as heterothallic eight‐spored N. crassa, fusion haploid nuclei is followed directly by meiosis a postmeiotic mitosis. These divisions take place within single unpartitioned giant cell, ascus, which...

The close synchrony of meiotic events within the basidiocarp Coprinus lagopus permits time sequence study division stages. It takes about 16 h from beginning karyogamy to completion meiosis (zygotene tetrad formation). Nuclear fusion and chromosome pairing occupy 4 h, pachytene 5 diplotene all other stages including second appear be very transitory together less than 3 h. centrosome divides at late diplotene. entire 1 hour different overlap a great deal. four sterigmata are formed after...

The term Barren is applied to perithecia (sexual fruiting bodies) that produce no or few ascospores. Perithecial number usually not reduced in barren crosses. condition may result from recessive dominant mutations, partial chromosome duplications, and occasionally balanced rearrangements. It characteristic of some but all the types genes increase radiation sensitivity deletion segmental duplication. Barrenness provides a convenient signal for these genotypes, where meiosis ascus development...

Each ascospore of Neurospora tetrasperma normally contains haploid nuclei both mating types, A and a, produces a self-fertile culture. majority cultures from single conidia are also self-fertile, because most multinucleate contain types. It has long been known that some single-mating type, self-sterile produced, either exceptional homokaryotic ascospores or the minority homokaryotic. The homokaryotic, crossfertile with strains opposite can be fertilized by compatible heterokaryotic cultures....

ABSTRACT Wild-collected isolates of Neurospora crassa Shear and Dodge were systematically examined for recessive mutations affecting the sexual phase life cycle, which is essentially diploid. Seventy-four 99 wild-collected from 26 populations in United States, India Pakistan carried one or more that reduced fertility significantly when homozygous; spore morphology also detected. Limited complementation tests indicate most 106 recovered are unique.—The diplophase (= phase) uncovered by...

Meiotic nuclear behavior and chromosome numbers have been examined, using a propionic–iron–hematoxylin staining method, in Neurospora crassa five homothallic species, N. africana, dodgei, galapagosensis, lineolata tcrricola. Ascus development, haploid (n = 7), morphology all species resemble the heterothallic crassa. The following observations not reported previously for any although some described other fungi. Most apply to except where otherwise indicated. (1) Chromosomes elongate...

ABSTRACT Crosses heterozygous and homozygous for Sk–1, Sk–2 Sk–3 were examined by light microscopy. All three Spore killers behave similarly. In heterozygoua killer x sensitive crosses, meiosis ascospore development are normal until after the second postmeiotic mitosis when four of eight ascospores in each ascus stop developing degenerate. The surviving carry killer. Death sensitives thus occurs only alleles, SkK SkS, have segregated into separate ascospores. Homozygous crosses do not show...

Abstract Neurospora crassa and related heterothallic ascomycetes produce eight homokaryotic self-sterile ascospores per ascus. In contrast, asci of N. tetrasperma contain four self-fertile each with nuclei both mating types (matA mata). The result from first-division segregation type nuclear spindle overlap at the second meiotic division a subsequent mitotic division. Recently, Merino et al. presented population-genetic evidence that crossing over is suppressed on mating-type chromosome...

The DNA-specific fluorochrome acriflavin has been used to stain meiotic chromosomes in Neurospora. method is simple and highly reliable. Acriflavin-stained nuclei show good contrast excellent resolution for detailed chromosome analysis. nucleolus organizer region can be seen as an attenuated strand embedded within the unstained ghost. Since spindles spindle pole bodies do not fluoresce at all, useful determining numbers during condensed division stages ascus.

Spore killers (Sk), studied most extensively in Neurospora, are also known Podospora, Gibberella and Cochliobolus. no doubt present natural populations of other fungi. Criteria outlined here for recognizing their presence distinguishing them from causes ascospore death. Killing occurs when one parent carries the killer element (SkK) sensitive counterpart (Sks). When heterozygous, every ascus contains four normal-sized, viable ascospores that tiny, undeveloped, inviable. expressed...

Abstract In Neurospora crassa, pairing of homologous DNA segments is monitored during meiotic prophase I. Any genes not paired with a homolog, as well any homologs that gene, are silenced the sexual phase by mechanism known silencing unpaired (MSUD). Two required for MSUD have been described previously: sad-1 (suppressor ascus dominance), encoding an RNA-directed RNA polymerase, and sad-2, protein controls perinuclear localization SAD-1. Inactivation either or sad-2 suppresses MSUD. We now...

ABSTRACT Meiotic synchrony in the genus Coprinus has permitted sequential study of spindle pole body (SPB) behaviour through meiotic process. The SPBs are monoglobular young basidia immediately after last premeiotic mitosis. From 10 to 15 h before karyogamy until pachytene, bodies not found. They become conspicuous diplotene and persist completion meiosis. During diplotene, metaphase, anaphase telophase stages but at late they duplicate diglobular with an isthmus connecting 2 globular...

Abstract It was shown previously that when a chromosomal Spore killer factor is heterozygous in Neurospora species with eight-spored asci, the four sensitive ascospores each ascus die and survivors are all killers. Sk-2K Sk-3K nonrecombining haplotypes segregate centromere of linkage group III. No killing occurs either one these killers homozygous, but to by other crosses x Sk-3K. In present study, were transferred recurrent backcrosses from crassa into tetrasperma, pseudohomothallic which...

ABSTRACT In translocation OY321 of Neurospora crassa, the nucleolus organizer is divided into two segments, a proximal portion located interstitially in one interchange chromosome, and distal now terminally on another linkage group I. crosses Translocation x Translocation, exceptional progeny are recovered nonselectively which chromosome sequence has apparently reverted to Normal. Genetic, cytological, molecular evidence indicates that reversion result meiotic crossing over between...