scholarly journals Misdivision of Telocentrics and Isochromosomes in Wheat

2019 ◽  
Vol 157 (3) ◽  
pp. 179-188 ◽  
Author(s):  
David Kopecky ◽  
Adam J. Lukaszewski
Keyword(s):  
Chromosome Length ◽  
General Relationship ◽  
Chromosome Size ◽  
Meiotic Behavior ◽  
Sister Chromatids ◽  
Normal Transition ◽  
Spindle Apparatus

For normal transition through meiosis, chromosomes rely on pairing with their homologues. Chromosomes which fail to pair, univalents, behave irregularly and may undergo various types of breakage across their centromeres. Here, we analyzed the meiotic behavior of misdivision products themselves: isochromosomes and telocentrics in wheat. Both types of chromosomes behaved in the same fashion as standard 2-armed chromosomes. The 2 most frequent scenarios were separation of sister chromatids in anaphase I or monopolar/bipolar attachment of the univalent to the spindle apparatus with unseparated chromatids. Misdivision was rare, and its frequency appeared directly related to the size of the centromere. The previously deduced relationship between misdivision frequency and chromosome size was likely erroneous and can be explained by a general relationship between chromosome length and the size of its centromere. Pairing of identical arms in isochromosomes did not protect them from misdivision. It is not chiasmate pairing that protects from misdivision but mechanistic issues that arise through that pairing.

scholarly journals Nucleic acid content and Chromosome morphology in Chrysanthemum

1969 ◽  
Vol 13 (3) ◽  
pp. 241-250 ◽  
Author(s):  
G. J. Dowrick ◽  
A. S. El Bayoumi
Keyword(s):  
Nucleic Acid ◽  
Chromosome Number ◽  
Dna Content ◽  
Chromosome Numbers ◽  
Chromosome Length ◽  
Chromosome Morphology ◽  
Nucleic Acid Content ◽  
Chromosome Size ◽  
Dna Contents ◽  
The Relationship

1. The DNA contents of twenty-eight different species and forms of Chrysanthemum have been measured by photometry. It is shown that there are large differences in DNA content between some species with identical chromosome numbers.2. The DNA contents of natural polyploids are frequently not those expected when comparison is made with diploid forms of the same species. The DNA contents of induced polyploids are those expected.3. Chromosome length and volume are positively correlated with DNA content.4. The relationship between chromosome number, chromosome size, DNA content and gene number is considered, and it is suggested that the differences in DNA content may result from the presence of differing amounts of genetically inactive DNA in the chromosomes.

scholarly journals The intranuclear relationship between centromere volume and chromosome size in Festuca scariosa X drymeja

1981 ◽  
Vol 47 (1) ◽  
pp. 117-125
Author(s):  
G. Jenkins ◽  
M.D. Bennett
Keyword(s):  
Serial Section ◽  
Chromosome Length ◽  
Individual Chromosome ◽  
Chromosome Size ◽  
Preferential Pairing ◽  
Frequency Distributions ◽  
Positive Correlation ◽  
Serial Section Reconstruction

In the hybrid Festuca scarisoa X drymeja where pairing is incomplete at pachytene, there is preferential pairing between the longer chromosomes of the complement. EM serial-section reconstruction of nuclei at zygotene and pachytene reveals that there is equally pronounced preferential pairing between larger centromeres. This evidence suggests that the longer chromosomes have large centromeres and that centromere volume is correlated with chromosome length. Confirmation of this comes from the comparison of the frequency distributions of observed centromere volumes and those predicted on the basis of chromosome length. Although there is a positive correlation between centromere volume and chromosome length, it is not possible to identify the centromeres of each individual chromosome within the complement because (a) the differences between the lengths of each chromosome are small and (b) the estimates of relative centromere volumes vary significantly between cells.

scholarly journals The effects of chromosome fusions on genetic diversity and evolutionary turnover of functional loci consistently depends on chromosome size

2021 ◽  
Author(s):  
Francesco Cicconardi ◽  
James J Lewis ◽  
Simon Henry Martin ◽  
Robert D. Reed ◽  
Charles G Danko ◽  
...  
Keyword(s):  
Chromosomal Rearrangements ◽  
Gc Content ◽  
Population Level ◽  
Chromosome Length ◽  
Adaptive Divergence ◽  
Chromosome Size ◽  
Turnover Rates ◽  
Chromosome Fusion ◽  
Chromosome Fusions ◽  
Chromosome Level

Major changes in chromosome number and structure are linked to a series of evolutionary phenomena, including intrinsic barriers to gene flow or suppression of recombination due to chromosomal rearrangements. However, chromosome rearrangements can also affect the fundamental dynamics of molecular evolution within populations by changing relationships between linked loci and altering rates of recombination. Here, we build chromosome-level assembly Eueides isabella and, together with the chromosome-level assembly of Dryas iulia, examine the evolutionary consequences of multiple chromosome fusions in Heliconius butterflies. These assemblies pinpoint fusion points on 10 of the 21 autosomal chromosomes and reveal striking differences in the characteristics of fused and unfused chromosomes. The ten smallest autosomes in D. iulia and E. isabella, which have each fused to a longer chromosome in Heliconius, have higher repeat and GC content, and longer introns than predicted by their chromosome length. Following fusion, these characteristics change to become more in line with chromosome length. The fusions also led to reduced diversity, which likely reflects increased background selection and selection against introgression between diverging populations, following a reduction in per-base recombination rate. We further show that chromosome size and fusion impact turnover rates of functional loci at a macroevolutionary scale. Together these results provide further evidence that chromosome fusion in Heliconius likely had dramatic effects on population level processes shaping rates of neutral and adaptive divergence. These effects may have impacted patterns of diversification in Heliconius, a classic example of an adaptive radiation.

scholarly journals Morphology and Meiotic Behavior of Three Dendrobium Amphidiploids and Their Diploid Counterparts

HortScience ◽  
1993 ◽  
Vol 28 (9) ◽  
pp. 935-937 ◽  
Author(s):  
James McConnell ◽  
H. Kamemoto
Keyword(s):  
Small Chromosome ◽  
Chromosome Size ◽  
Meiotic Behavior ◽  
Preferential Pairing ◽  
Bivalent Formation ◽  
Metaphase I

Floral characteristics, meiotic behavior, and sporad formation were compared in three Dendrobium tetraploids (amphidiploids) and their diploid counterparts. Amphidiploid flowers were larger than those of diploids. Diploid meiotic behavior varied; mean configurations at Metaphase I ranged from 14.3 bivalents and 9.4 univalents to 18.9 bivalents and 0.2 univalents. In amphidiploids, nearly all cells had 38 bivalents. Sporad formation also varied; diploids had 36% to 70% tetrads and amphidiploids had 97% to 100% tetrads. Preferential pairing and small chromosome size may promote bivalent formation in amphidiploids.

scholarly journals Positive and Negative Roles of Homologous Recombination in the Maintenance of Genome Stability inSaccharomyces cerevisiae

Genetics ◽  
2003 ◽  
Vol 164 (1) ◽  
pp. 31-46 ◽  
Author(s):  
Jumpei Yoshida ◽  
Keiko Umezu ◽  
Hisaji Maki
Keyword(s):  
Homologous Recombination ◽  
Loss Of Heterozygosity ◽  
Genome Stability ◽  
Point Mutations ◽  
Chromosome Loss ◽  
Chromosome Size ◽  
Sister Chromatids ◽  
Chromosome Iii ◽  
Ura3 Marker

AbstractIn previous studies of the loss of heterozygosity (LOH), we analyzed a hemizygous URA3 marker on chromosome III in S. cerevisiae and showed that homologous recombination is involved in processes that lead to LOH in multiple ways, including allelic recombination, chromosome size alterations, and chromosome loss. To investigate the role of homologous recombination more precisely, we examined LOH events in rad50Δ, rad51Δ, rad52Δ, rad50Δ rad52Δ, and rad51Δ rad52Δ mutants. As compared to Rad+ cells, the frequency of LOH was significantly increased in all mutants, and most events were chromosome loss. Other LOH events were differentially affected in each mutant: the frequencies of all types of recombination were decreased in rad52 mutants and enhanced in rad50 mutants. The rad51 mutation increased the frequency of ectopic but not allelic recombination. Both the rad52 and rad51 mutations increased the frequency of intragenic point mutations ∼25-fold, suggesting that alternative mutagenic pathways partially substitute for homologous recombination. Overall, these results indicate that all of the genes are required for chromosome maintenance and that they most likely function in homologous recombination between sister chromatids. In contrast, other recombination pathways can occur at a substantial level even in the absence of one of the genes and contribute to generating various chromosome rearrangements.

scholarly journals CENP-A and topoisomerase-II antagonistically affect chromosome length

2017 ◽  
Vol 216 (9) ◽  
pp. 2645-2655 ◽  
Author(s):  
A.-M. Ladouceur ◽  
Rajesh Ranjan ◽  
Lydia Smith ◽  
Tanner Fadero ◽  
Jennifer Heppert ◽  
...  
Keyword(s):  
Self Assembly ◽  
Topoisomerase Ii ◽  
Chromosome Length ◽  
Chromosome Size ◽  
Mitotic Chromosomes ◽  
Nuclear Trafficking ◽  
C Elegans ◽  
Protein Levels ◽  
Histone H3 Variant ◽  
Topo Ii

The size of mitotic chromosomes is coordinated with cell size in a manner dependent on nuclear trafficking. In this study, we conducted an RNA interference screen of the Caenorhabditis elegans nucleome in a strain carrying an exceptionally long chromosome and identified the centromere-specific histone H3 variant CENP-A and the DNA decatenizing enzyme topoisomerase-II (topo-II) as candidate modulators of chromosome size. In the holocentric organism C. elegans, CENP-A is positioned periodically along the entire length of chromosomes, and in mitosis, these genomic regions come together linearly to form the base of kinetochores. We show that CENP-A protein levels decreased through development coinciding with chromosome-size scaling. Partial loss of CENP-A protein resulted in shorter mitotic chromosomes, consistent with a role in setting chromosome length. Conversely, topo-II levels were unchanged through early development, and partial topo-II depletion led to longer chromosomes. Topo-II localized to the perimeter of mitotic chromosomes, excluded from the centromere regions, and depletion of topo-II did not change CENP-A levels. We propose that self-assembly of centromeric chromatin into an extended linear array promotes elongation of the chromosome, whereas topo-II promotes chromosome-length shortening.

scholarly journals Mammalian chromosome–telomere length dynamics

2018 ◽  
Vol 5 (7) ◽  
pp. 180492 ◽  
Author(s):  
Amy R. Klegarth ◽  
Dan T. A. Eisenberg
Keyword(s):  
Telomere Length ◽  
Significant Relationship ◽  
Chromosome Length ◽  
Individual Chromosome ◽  
Chromosome Size ◽  
Lag Effects ◽  
Phylogenetic Framework ◽  
Telomere Biology ◽  
Evolutionary Lag ◽  
Positive Correlations

Individual chromosome arms have specific individual telomere lengths (TLs). Past studies within species have shown strong positive correlations between individual chromosome length and TL at that chromosome. While the reasons for these associations are unclear, the strength and consistency of the associations across disparate taxa suggest that this is important to telomere biology and should be explored further. If TL is primarily determined by chromosome length, then chromosome length should be considered and controlled for in cross-species analyses of TL. Here, we employ a cross-species approach to explore whether the chromosome length–TL association observed intraspecifically is a determinant of mean TL across species. Data were compiled from two studies characterizing TL across a range of mammalian taxa and analysed in a phylogenetic framework. We found no significant relationship between TL and chromosome size across mammals or within mammalians orders. The pattern trends in the expected direction and we suggest may be masked by evolutionary lag effects.

scholarly journals DNA loops generate intracentromere tension in mitosis

2015 ◽  
Vol 210 (4) ◽  
pp. 553-564 ◽  
Author(s):  
Josh Lawrimore ◽  
Paula A. Vasquez ◽  
Michael R. Falvo ◽  
Russell M. Taylor ◽  
Leandra Vicci ◽  
...  
Keyword(s):  
Dna Looping ◽  
Biological Mechanism ◽  
Dna Loops ◽  
Checkpoint Kinase ◽  
Chromatin Loops ◽  
Microtubule Attachment ◽  
Sister Chromatids ◽  
Spindle Apparatus ◽  
Physical Consequences ◽  
Sister Centromere

The centromere is the DNA locus that dictates kinetochore formation and is visibly apparent as heterochromatin that bridges sister kinetochores in metaphase. Sister centromeres are compacted and held together by cohesin, condensin, and topoisomerase-mediated entanglements until all sister chromosomes bi-orient along the spindle apparatus. The establishment of tension between sister chromatids is essential for quenching a checkpoint kinase signal generated from kinetochores lacking microtubule attachment or tension. How the centromere chromatin spring is organized and functions as a tensiometer is largely unexplored. We have discovered that centromere chromatin loops generate an extensional/poleward force sufficient to release nucleosomes proximal to the spindle axis. This study describes how the physical consequences of DNA looping directly underlie the biological mechanism for sister centromere separation and the spring-like properties of the centromere in mitosis.

Birefringence and Ultrastructure of Isolated, Stabilized Spindles

1976 ◽  
Vol 34 ◽  
pp. 64-65
Author(s):  
James R. LaFountain ◽  
Robert L. Evans
Keyword(s):  
Fiber Birefringence ◽  
Spindle Apparatus

Previous investigations on the spindle apparatus in primary spermatocytes of the crane fly, Nephrotoma suturalis, with polarizing optics have shown that chromosomal fibers can be detected as positively birefringent bands extending from the chromosomes to the poles (1). Chromosomal fiber birefringence reaches a maximum at metaphase when five distinct fibers can be seen in each half spindle. An obvious question raised by these results was what is the ultrastructural basis of birefringence?Initial attempts to characterize the ultrastructure of crane-fly spindles showed that there were hundreds of microtubules (MTs) in these spindles, but there was no evidence that they were distributed in a pattern that corresponded to the pattern of birefringence (2,3).

Centromere assembly and non-random sister chromatid segregation in stem cells

2020 ◽  
Vol 64 (2) ◽  
pp. 223-232 ◽  
Author(s):  
Ben L. Carty ◽  
Elaine M. Dunleavy
Keyword(s):  
Stem Cells ◽  
Cell Division ◽  
Cell Fate ◽  
Sister Chromatid ◽  
Asymmetric Cell Division ◽  
Protein A ◽  
Germline Stem Cells ◽  
Sister Chromatids ◽  
Centromere Protein A ◽  
Oocyte Meiosis

Abstract Asymmetric cell division (ACD) produces daughter cells with separate distinct cell fates and is critical for the development and regulation of multicellular organisms. Epigenetic mechanisms are key players in cell fate determination. Centromeres, epigenetically specified loci defined by the presence of the histone H3-variant, centromere protein A (CENP-A), are essential for chromosome segregation at cell division. ACDs in stem cells and in oocyte meiosis have been proposed to be reliant on centromere integrity for the regulation of the non-random segregation of chromosomes. It has recently been shown that CENP-A is asymmetrically distributed between the centromeres of sister chromatids in male and female Drosophila germline stem cells (GSCs), with more CENP-A on sister chromatids to be segregated to the GSC. This imbalance in centromere strength correlates with the temporal and asymmetric assembly of the mitotic spindle and potentially orientates the cell to allow for biased sister chromatid retention in stem cells. In this essay, we discuss the recent evidence for asymmetric sister centromeres in stem cells. Thereafter, we discuss mechanistic avenues to establish this sister centromere asymmetry and how it ultimately might influence cell fate.

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