scholarly journals Synaptic adjustment of inversion loops in Neurospora crassa.

Genetics ◽  
1990 ◽  
Vol 124 (3) ◽  
pp. 593-598
Author(s):  
M Bojko
Keyword(s):  
Neurospora Crassa ◽  
Electron Micrographs ◽  
Meiotic Prophase ◽  
Chromosome 1 ◽  
Inverted Region ◽  
Nonhomologous Synapsis

Abstract Heterozygotes for three long inversions on chromosome 1 were analyzed by serial reconstruction from electron micrographs. Measurements of loop lengths at different meiotic prophase substages revealed that the homologous synapsis of the inverted region was gradually replaced by nonhomologous synapsis as loops were eliminated during pachytene. This synaptic adjustment was apparently not affected by crossovers which occurred within the 150- and 160-cM long loops.

scholarly journals Evidence on the nature and complexity of the mechanism of chiasma maintenance in maize

1985 ◽  
Vol 45 (1) ◽  
pp. 37-49 ◽  
Author(s):  
Marjorie P. Maguire
Keyword(s):  
Linear Relationship ◽  
Sister Chromatid ◽  
Paracentric Inversion ◽  
Chromosome 1 ◽  
Crossing Over ◽  
Inverted Region ◽  
Maintenance Mechanism ◽  
Paracentric Inversions

SummaryInferences on the mechanism of chiasma maintenance can be drawn from study of the distribution and frequency of chiasma-like associations between bridges and fragments and between normal chromatids and fragments in meiotic material heterozygous for paracentric inversions. These bridges and fragments are the result of crossing over within the inverted region so that differing predictions for the associations are generated by the various models for chiasma maintenance mechanism. Results of such a study in material heterozygous for a large paracentric inversion in the long arm of chromosome 1 in maize are reported here. Findings are generally consistent with predictions of the ‘generalized sister chromatid cohesiveness model’, but are markedly at odds with the ‘binder only at specific crossover sites model’, and with the ‘late effective doubling of telomeres model’. Some of the results do not conform quantitatively to predictions of the ‘generalized sister chromatid cohesiveness model’ for a linear relationship between potential extent of sister chromatid cohesiveness and frequency of maintained association, suggesting additional complexity.

Ascus development in two temperature-sensitive Four-spore mutants of Neurospora crassa

1986 ◽  
Vol 28 (6) ◽  
pp. 982-990 ◽  
Author(s):  
Namboori B. Raju
Keyword(s):  
Neurospora Crassa ◽  
High Temperatures ◽  
Low Temperatures ◽  
Meiotic Prophase ◽  
Temperature Shift ◽  
Sensitive Period ◽  
Temperature Sensitive ◽  
Limited Temperature ◽  
Increasing Temperature ◽  
Two Temperature

Two nonallelic Four-spore mutants are known in which ascospore walls enclose the four immediate products of meiosis rather than the normal eight products of a postmeiotic mitosis. Expression depends on temperature. The Four-spore phenotype is expressed when the developing asci are subjected either to high temperatures (25–30 °C) for Fsp-1 or to low temperatures (15–20 °C) for Fsp-2. Heterozygous Fsp-1 × Fsp-1+ crosses make eight-spored asci at 15–20 °C but produce many four-spored asci at 25 °C and mostly four-spored asci at 30 °C. Homozygous Fsp-1 × Fsp-1 crosses respond similarly to increasing temperature but make 40–50% four-spored asci even at 20 °C. Heterozygous Fsp-2 × Fsp-2+ crosses produce almost exclusively four-spored asci at 15 °C but a mixture of four- and eight-spored asci at 20, 25, and 30 °C. Homozygous Fsp-2 × Fsp-2 crosses make all four-spored asci at 15 and 20 °C and a mixture of four- and eight-spored asci at 25 and 30 °C. When both Fsp-1 and Fsp-2 are present in a cross, either homozygous or heterozygous, no asci contain more than four ascospores at any temperature. Limited temperature-shift experiments with Fsp-1 and Fsp-2 show that the sensitive period for Four-spore expression is sometime after meiotic prophase, possibly at interphase II.Key words: Neurospora, temperature sensitive, Four-spore mutants, large ascospores.

Pericentric inversion in natural populations of Oligoryzomys nigripes (Rodentia: Sigmodontinae)

Genome ◽  
2001 ◽  
Vol 44 (5) ◽  
pp. 791-796 ◽  
Author(s):  
Cibele R Bonvicino ◽  
Paulo S D'Andrea ◽  
Pavel M Borodin
Keyword(s):  
Electron Microscopy ◽  
Pericentric Inversion ◽  
Natural Populations ◽  
Chromosome 3 ◽  
Crossing Over ◽  
Inverted Region ◽  
Meiotic Analysis ◽  
Hardy Weinberg Equilibrium ◽  
Heterozygous Carriers ◽  
Nonhomologous Synapsis

We analysed polymorphism for pericentric inversion in chromosome 3 of Oligoryzomys nigripes (Rodentia: Sigmodontinae) in several populations in Brazil and examined the meiotic behaviour of this chromosome in heterozygotes. We observed an orderly pairing of all chromosomes at pachytene in heterozygotes for the inverted chromosome 3. No indication of meiotic arrest and germ-cell death was found. Electron microscopy of synaptonemal complexes and conventional meiotic analysis indicated strictly nonhomologous synapsis and crossing-over suppression in the inverted region in the heterozygotes, which prevent the formation of unbalanced gametes. Thus, the pericentric inversion in chromosome 3 does not apparently result in any selective disadvantages in heterozygous carriers. In the majority of the populations studied, the frequencies of acrocentric homozygotes, metacentric homozygotes, and heterozygotes were in Hardy–Weinberg equilibrium. However, in some populations, we detected an excess of heterozygotes and a deficiency of acrocentric homozygotes.Key words: chromosome rearrangements, inversion, meiosis, Oligoryzomys nigripes.

scholarly journals The relationship of homologous synapsis and crossing over in a maize inversion.

Genetics ◽  
1994 ◽  
Vol 137 (1) ◽  
pp. 281-288 ◽  
Author(s):  
M P Maguire ◽  
R W Riess
Keyword(s):  
Electron Micrographs ◽  
Crossing Over ◽  
Inverted Region ◽  
Recombination Nodule ◽  
Recombination Nodules ◽  
Reciprocal Recombination ◽  
Relationship Of ◽  
The Relationship

Abstract Frequency of homologous synapsis at pachytene for a relatively short heterozygous inversion was compared to the frequency of crossover occurrence within the inversion and to the frequency of the presence of a recombination nodule within the homologously synapsed inverted region. Crossover frequencies were estimated from bridge-fragment frequencies at anaphase I and anaphase II. Recombination nodules (RNs) were observed in electron micrographs. Results show very similar frequencies of homologous synapsis and the occurrence of reciprocal recombination within the inverted region, consistent with the interpretation that establishment of homologous synapsis in this case is related to at least commitment to the form of resolution of crossover intermediates which gives rise to reciprocal recombination, not conversion only, events. An RN was generally found at pachytene in homologously synapsed inverted regions.

Thepam1Gene Is Required for Meiotic Bouquet Formation and Efficient Homologous Synapsis in Maize (Zea maysL.)

Genetics ◽  
2002 ◽  
Vol 162 (4) ◽  
pp. 1979-1993 ◽  
Author(s):  
Inna N Golubovskaya ◽  
Lisa C Harper ◽  
Wojciech P Pawlowski ◽  
Denise Schichnes ◽  
W Zacheus Cande
Keyword(s):  
Nuclear Envelope ◽  
Meiotic Prophase ◽  
Homologous Chromosome ◽  
Rare Event ◽  
Intermediate Stage ◽  
Wild Type ◽  
Prophase I ◽  
Chromosome Synapsis ◽  
Nonhomologous Synapsis ◽  
Maize Gene

AbstractThe clustering of telomeres on the nuclear envelope (NE) during meiotic prophase to form the bouquet arrangement of chromosomes may facilitate homologous chromosome synapsis. The pam1 (plural  abnormalities of  meiosis  1) gene is the first maize gene that appears to be required for telomere clustering, and homologous synapsis is impaired in pam1. Telomere clustering on the NE is arrested or delayed at an intermediate stage in pam1. Telomeres associate with the NE during the leptotene-zygotene transition but cluster slowly if at all as meiosis proceeds. Intermediate stages in telomere clustering including miniclusters are observed in pam1 but not in wild-type meiocytes. The tight bouquet normally seen at zygotene is a rare event. In contrast, the polarization of centromeres vs. telomeres in the nucleus at the leptotene-zygotene transition is the same in mutant and wild-type cells. Defects in homologous chromosome synapsis include incomplete synapsis, nonhomologous synapsis, and unresolved interlocks. However, the number of RAD51 foci on chromosomes in pam1 is similar to that of wild type. We suggest that the defects in homologous synapsis and the retardation of prophase I arise from the irregularity of telomere clustering and propose that pam1 is involved in the control of bouquet formation and downstream meiotic prophase I events.

Utilizing Dark Field Electron Microscopy to Produce Lantern Slides

1974 ◽  
Vol 32 ◽  
pp. 116-117
Author(s):  
J. N. Meador ◽  
C. N. Sun ◽  
H. J. White
Keyword(s):  
Electron Microscope ◽  
Electron Micrographs ◽  
Dark Field ◽  
Limiting Factor ◽  
Clinical Laboratories ◽  
Field Electron ◽  
Time Element ◽  
Field Electron Microscopy ◽  
Dark Field Electron ◽  
Dark Field Micrographs

The electron microscope is being utilized more and more in clinical laboratories for pathologic diagnosis. One of the major problems in the utilization of the electron microscope for diagnostic purposes is the time element involved. Recent experimentation with rapid embedding has shown that this long phase of the process can be greatly shortened. In rush cases the making of projection slides can be eliminated by taking dark field electron micrographs which show up as a positive ready for use. The major limiting factor for use of dark field micrographs is resolution. However, for conference purposes electron micrographs are usually taken at 2.500X to 8.000X. At these low magnifications the resolution obtained is quite acceptable.

Light Optical Diffraction Studies of Macromolecular Ultrastructure

1970 ◽  
Vol 28 ◽  
pp. 258-259
Author(s):  
Glen B. Haydon
Keyword(s):  
High Resolution ◽  
Diffraction Analysis ◽  
Diffraction Pattern ◽  
Electron Micrographs ◽  
Optical Diffraction ◽  
Electron Micrograph ◽  
Its Analysis ◽  
Resolution Electron ◽  
Diffraction Patterns

Analysis of light optical diffraction patterns produced by electron micrographs can easily lead to much nonsense. Such diffraction patterns are referred to as optical transforms and are compared with transforms produced by a variety of mathematical manipulations. In the use of light optical diffraction patterns to study periodicities in macromolecular ultrastructures, a number of potential pitfalls have been rediscovered. The limitations apply to the formation of the electron micrograph as well as its analysis.(1) The high resolution electron micrograph is itself a complex diffraction pattern resulting from the specimen, its stain, and its supporting substrate. Cowley and Moodie (Proc. Phys. Soc. B, LXX 497, 1957) demonstrated changing image patterns with changes in focus. Similar defocus images have been subjected to further light optical diffraction analysis.

On an Application of the Metallurgical Stage to Chromosome Morphology

1967 ◽  
Vol 25 ◽  
pp. 28-29
Author(s):  
Godfrey C. Hoskins
Keyword(s):  
Human Chromosome ◽  
Electron Micrographs ◽  
Chromosome Morphology ◽  
Electron Optics ◽  
Electron Micrograph ◽  
Photographic Evidence ◽  
Sophisticated Equipment ◽  
Periodic Arrangement

The first serious electron microscooic studies of chromosomes accompanied by pictures were by I. Elvers in 1941 and 1943. His prodigious study, from the manufacture of micronets to the development of procedures for interpreting electron micrographs has gone all but unnoticed. The application of todays sophisticated equipment confirms many of the findings he gleaned from interpretation of images distorted by the electron optics of that time. In his figure 18 he notes periodic arrangement of pepsin sensitive “prickles” now called secondary fibers. In his figure 66 precise regularity of arrangement of these fibers can be seen. In his figure 22 he reproduces Siegbahn's first stereoscopic electron micrograph of chromosomes.The two stereoscopic pairs of electron micrographs of a human chromosome presented here were taken with a metallurgical stage on a Phillips EM200. These views are interpreted as providing photographic evidence that primary fibers (1°F) about 1,200Å thick are surrounded by secondary fibers (2°F) arranged in regular intervals of about 2,800Å in this metanhase human chromosome. At the telomere the primary fibers bend back on themselves and entwine through the center of each of each chromatid. The secondary fibers are seen to continue to surround primary fibers at telomeres. Thus at telomeres, secondary fibers present a surface not unlike that of the side of the chromosome, and no more susceptible to the addition of broken elements from other chromosomes.

Criteria and Methods for Reliable Three-Dimensional Image Reconstruction

1974 ◽  
Vol 32 ◽  
pp. 330-331
Author(s):  
R. A. Crowther
Keyword(s):  
Image Reconstruction ◽  
Finite Number ◽  
Density Distribution ◽  
Electron Micrographs ◽  
Mathematical Problem ◽  
Three Dimensional ◽  
Ideal Case ◽  
Dimensional Image ◽  
General Object ◽  
The Ideal

The reconstruction of a three-dimensional image of a specimen from a set of electron micrographs reduces, under certain assumptions about the imaging process in the microscope, to the mathematical problem of reconstructing a density distribution from a set of its plane projections.In the absence of noise we can formulate a purely geometrical criterion, which, for a general object, fixes the resolution attainable from a given finite number of views in terms of the size of the object. For simplicity we take the ideal case of projections collected by a series of m equally spaced tilts about a single axis.

Some Structural Features of Metaphase Chromosomes of Mice and Men

1967 ◽  
Vol 25 ◽  
pp. 190-191
Author(s):  
Godfrey C. Hoskins ◽  
Betty B. Hoskins
Keyword(s):  
Electron Microscopy ◽  
Electron Micrographs ◽  
Structural Features ◽  
Metaphase Chromosomes ◽  
The Future ◽  
Of Mice And Men ◽  
Mouse Cells ◽  
Human And Mouse

Metaphase chromosomes from human and mouse cells in vitro are isolated by micrurgy, fixed, and placed on grids for electron microscopy. Interpretations of electron micrographs by current methods indicate the following structural features.Chromosomal spindle fibrils about 200Å thick form fascicles about 600Å thick, wrapped by dense spiraling fibrils (DSF) less than 100Å thick as they near the kinomere. Such a fascicle joins the future daughter kinomere of each metaphase chromatid with those of adjacent non-homologous chromatids to either side. Thus, four fascicles (SF, 1-4) attach to each metaphase kinomere (K). It is thought that fascicles extend from the kinomere poleward, fray out to let chromosomal fibrils act as traction fibrils against polar fibrils, then regroup to join the adjacent kinomere.

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