scholarly journals Whole-chromosome fusions in the karyotype evolution of Sceloporus (Iguania, Reptilia) are more intense in sex chromosomes than autosomes

2020 ◽  
Author(s):  
Artem P. Lisachov ◽  
Katerina V. Tishakova ◽  
Svetlana A. Romanenko ◽  
Anna S. Molodtseva ◽  
Dmitry Yu. Prokopov ◽  
...  
Keyword(s):  
Sex Chromosomes ◽  
Complex Analysis ◽  
Sex Chromosome ◽  
Chromosome 11 ◽  
Evolutionary Forces ◽  
Chromosome Synapsis ◽  
Synaptonemal Complex Analysis ◽  
Chromosome Fusions ◽  
Chromosome Formation ◽  
Pseudoautosomal Regions

AbstractThere is a growing body of evidence that the common ancestor of vertebrates had a bimodal karyotype, i.e. consisting of large macrochromosomes and small microchromosomes. This type of karyotype organization is preserved in most reptiles. However, certain species independently experience microchromosome fusions. The evolutionary forces behind this are unclear. We investigated the karyotype of the green spiny lizard, Sceloporus malachiticus, an iguana species which has 2n=22, whereas the ancestral karyotype of iguanas had 2n=36. We obtained and sequenced flow-sorted chromosome-specific DNA samples and found that most of the microchromosome fusions in this species involved sex chromosomes. We found that certain ancestral squamate chromosomes, such as the homologue of the Anolis carolinensis chromosome 11, are repeatedly involved in sex chromosome formation in different species. To test the hypothesis that the karyotypic shift could be associated with changes in recombination patterns, and to study sex chromosome synapsis and recombination in meiosis, we performed synaptonemal complex analysis in this species and in S. variabilis, a related species with 2n=34. We found that in the species studied the recombination patterns correlate more with phylogeny than with the structure of the karyotype. The sex chromosomes had two distal pseudoautosomal regions and a medial differentiated region.

scholarly journals Whole-chromosome fusions in the karyotype evolution of Sceloporus (Iguania, Reptilia) are more frequent in sex chromosomes than autosomes

2021 ◽  
Vol 376 (1833) ◽  
pp. 20200099
Author(s):  
Artem P. Lisachov ◽  
Katerina V. Tishakova ◽  
Svetlana A. Romanenko ◽  
Anna S. Molodtseva ◽  
Dmitry Yu. Prokopov ◽  
...  
Keyword(s):  
Sex Chromosomes ◽  
Recombination Rate ◽  
Complex Analysis ◽  
Chromosome Evolution ◽  
Sex Chromosome ◽  
Comparative Genomic ◽  
Synaptonemal Complex Analysis ◽  
Chromosome Fusions ◽  
Chromosome Formation ◽  
Pseudoautosomal Regions

Whole-chromosome fusions play a major role in the karyotypic evolution of reptiles. It has been suggested that certain chromosomes tend to fuse with sex chromosomes more frequently than others. However, the comparative genomic synteny data are too scarce to draw strong conclusions. We obtained and sequenced chromosome-specific DNA pools of Sceloporus malachiticus , an iguanian species which has experienced many chromosome fusions. We found that four of seven lineage-specific fusions involved sex chromosomes, and that certain syntenic blocks which constitute the sex chromosomes, such as the homologues of the Anolis carolinensis chromosomes 11 and 16, are repeatedly involved in sex chromosome formation in different squamate species. To test the hypothesis that the karyotypic shift could be associated with changes in recombination patterns, we performed a synaptonemal complex analysis in this species and in Sceloporus variabilis (2 n = 34). It revealed that the sex chromosomes in S. malachiticus had two distal pseudoautosomal regions and a medial differentiated region. We found that multiple fusions little affected the recombination rate in S. malachiticus . Our data confirm more frequent involvement of certain chromosomes in sex chromosome formation, but do not reveal a connection between the gonosome–autosome fusions and the evolution of recombination rate. This article is part of the theme issue ‘Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)’.

scholarly journals Evolutionary Dynamics of Sex Chromosomes of Paleognathous Birds

2019 ◽  
Vol 11 (8) ◽  
pp. 2376-2390 ◽  
Author(s):  
Luohao Xu ◽  
Simon Yung Wa Sin ◽  
Phil Grayson ◽  
Scott V Edwards ◽  
Timothy B Sackton
Keyword(s):  
Sex Chromosomes ◽  
Evolutionary Dynamics ◽  
Chromosome Evolution ◽  
Sex Chromosome ◽  
Z Chromosome ◽  
Recombination Suppression ◽  
Evolutionary Forces ◽  
Genomic Level ◽  
Standard Models ◽  
Pseudoautosomal Regions

Abstract Standard models of sex chromosome evolution propose that recombination suppression leads to the degeneration of the heterogametic chromosome, as is seen for the Y chromosome in mammals and the W chromosome in most birds. Unlike other birds, paleognaths (ratites and tinamous) possess large nondegenerate regions on their sex chromosomes (PARs or pseudoautosomal regions). It remains unclear why these large PARs are retained over >100 Myr, and how this retention impacts the evolution of sex chromosomes within this system. To address this puzzle, we analyzed Z chromosome evolution and gene expression across 12 paleognaths, several of whose genomes have recently been sequenced. We confirm at the genomic level that most paleognaths retain large PARs. As in other birds, we find that all paleognaths have incomplete dosage compensation on the regions of the Z chromosome homologous to degenerated portions of the W (differentiated regions), but we find no evidence for enrichments of male-biased genes in PARs. We find limited evidence for increased evolutionary rates (faster-Z) either across the chromosome or in differentiated regions for most paleognaths with large PARs, but do recover signals of faster-Z evolution in tinamou species with mostly degenerated W chromosomes, similar to the pattern seen in neognaths. Unexpectedly, in some species, PAR-linked genes evolve faster on average than genes on autosomes, suggested by diverse genomic features to be due to reduced efficacy of selection in paleognath PARs. Our analysis shows that paleognath Z chromosomes are atypical at the genomic level, but the evolutionary forces maintaining largely homomorphic sex chromosomes in these species remain elusive.

scholarly journals Evolutionary dynamics of sex chromosomes of paleognathous birds

2018 ◽  
Author(s):  
Luohao Xu ◽  
Simon Yung Wa Sin ◽  
Phil Grayson ◽  
Scott V. Edwards ◽  
Timothy B. Sackton
Keyword(s):  
Sex Chromosomes ◽  
Evolutionary Dynamics ◽  
Chromosome Evolution ◽  
Sex Chromosome ◽  
Z Chromosome ◽  
Recombination Suppression ◽  
Evolutionary Forces ◽  
Genomic Level ◽  
Standard Models ◽  
Pseudoautosomal Regions

AbstractStandard models of sex chromosome evolution propose that recombination suppression leads to the degeneration of the heterogametic chromosome, as is seen for the Y chromosome in mammals and the W chromosome in most birds. Unlike other birds, paleognaths (ratites and tinamous) possess large non-degenerate regions on their sex chromosomes (PARs or pseudoautosomal regions). It remains unclear why these large PARs are retained over more than 100 MY, and how this retention impacts the evolution of sex chromosomes within this system. To address this puzzle, we analysed Z chromosome evolution and gene expression across 12 paleognaths, several of whose genomes have recently been sequenced. We confirm at the genomic level that most paleognaths retain large PARs. As in other birds, we find that all paleognaths have incomplete dosage compensation on the regions of the Z chromosome homologous to degenerated portions of the W (differentiated regions or DRs), but we find no evidence for enrichments of male-biased genes in PARs. We find limited evidence for increased evolutionary rates (faster-Z) either across the chromosome or in DRs for most paleognaths with large PARs, but do recover signals of faster-Z evolution in tinamou species with mostly degenerated W chromosomes, similar to the pattern seen in neognaths. Unexpectedly, in some species PAR-linked genes evolve faster on average than genes on autosomes, suggested by diverse genomic features to be due to reduced efficacy of selection in paleognath PARs. Our analysis shows that paleognath Z chromosomes are atypical at the genomic level, but the evolutionary forces maintaining largely homomorphic sex chromosomes in these species remain elusive.

Synaptonemal complex analysis in spermatocytes of tilapia, Oreochromis niloticus (Pisces, Cichlidae)

Genome ◽  
1993 ◽  
Vol 36 (6) ◽  
pp. 1124-1128 ◽  
Author(s):  
Fausto Foresti ◽  
Claudio Oliveira ◽  
Pedro Manoel Galetti Junior ◽  
Lurdes Foresti de Almeida-Toledo
Keyword(s):  
Synaptonemal Complex ◽  
Sex Chromosomes ◽  
Oreochromis Niloticus ◽  
Complex Analysis ◽  
Sex Chromosome ◽  
Light And Electron Microscopy ◽  
Nucleolus Organizer ◽  
Nucleolus Organizer Regions ◽  
Synaptonemal Complex Analysis ◽  
Sex Chromosome System

Some adaptations of the synaptonemal complex (SC) whole-mounting technique first used in plants permitted its application to meiotic studies in tilapia, Oreochromis niloticus. Direct observation of the chromosome pairing process and bivalent structure during the meiotic prophase of this fish species by light and electron microscopy permitted the analysis of SCs in autosomes and the possible identification of sex chromosomes. The analysis of SCs in spermatocytes of O. niloticus revealed that all 22 bivalent chromosomes completely paired, except for the occurrence of a size heteromorphism in the terminal region of the largest bivalent associated with the presence of an incompletely paired segment during the synapsis process, which may be the cytological visualization of an XX/XY sex chromosome system in this species.Key words: fish cytogenetics, synaptonemal complex, fish meiosis, sex chromosomes, nucleolus organizer regions.

Synaptonemal Complex Analysis of Sex Chromosomes in Two Species of Sceloporus

Copeia ◽  
1990 ◽  
Vol 1990 (4) ◽  
pp. 1122 ◽  
Author(s):  
Kent M. Reed ◽  
Philip D. Sudman ◽  
Jack W. Sites ◽  
Ira F. Greenbaum
Keyword(s):  
Synaptonemal Complex ◽  
Sex Chromosomes ◽  
Complex Analysis ◽  
Synaptonemal Complex Analysis

scholarly journals Chromosome fusions shape an ancient UV sex chromosome system

2020 ◽  
Author(s):  
Sarah B. Carey ◽  
Jerry Jenkins ◽  
Adam C. Payton ◽  
Shenqiang Shu ◽  
John T. Lovell ◽  
...  
Keyword(s):  
Gene Regulatory Networks ◽  
Sex Chromosomes ◽  
Regulatory Networks ◽  
Sex Chromosome ◽  
Structural Complexity ◽  
Sex Chromosome System ◽  
Chromosome Fusions ◽  
Gene Regulatory ◽  
Suppressed Recombination ◽  
Reference Genomes

AbstractSex chromosomes occur in diverse organisms, but their structural complexity has often prevented evolutionary analyses. Here we use two chromosome-scale reference genomes of the moss Ceratodon purpureus to trace the evolution of the sex chromosomes in bryophytes. Comparative analyses show the moss genome comprises seven remarkably stable ancestral chromosomal elements. An exception is the sex chromosomes, which share thousands of broadly-expressed genes but lack any synteny. We show the sex chromosomes evolved over 300 million years ago and expanded via at least two distinct chromosomal fusions. These results link suppressed recombination between the sex chromosomes with rapid structural change and the evolution of distinct transposable element compositions, and suggest haploid gene expression promotes the evolution of independent female and male gene-regulatory networks.One Sentence SummaryMoss sex chromosomes retain thousands of broadly-expressed genes despite millions of years of suppressed recombination.

scholarly journals Genetic diversity on the human X chromosome does not support a strict pseudoautosomal boundary

2015 ◽  
Author(s):  
Daniel J Cotter ◽  
Sarah M Brotman ◽  
Melissa A Wilson Sayres
Keyword(s):  
Genetic Diversity ◽  
X Chromosome ◽  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Gradual Reduction ◽  
Noncoding Regions ◽  
Pseudoautosomal Regions ◽  
Linked Selection ◽  
Human Specific ◽  
Pseudoautosomal Boundary

Unlike the autosomes, recombination between the X chromosome and Y chromosome often thought to be constrained to two small pseudoautosomal regions (PARs) at the tips of each sex chromosome. The PAR1 spans the first 2.7 Mb of the proximal arm of the human sex chromosomes, while the much smaller PAR2 encompasses the distal 320 kb of the long arm of each sex chromosome. In addition to the PAR1 and PAR2, there is a human-specific X-transposed region that was duplicated from the X to the Y. The X-transposed region is often not excluded from X-specific analyses, unlike the PARs, because it is not thought to routinely recombine. Genetic diversity is expected to be higher in recombining regions than in non-recombining regions because recombination reduces the effect of linked selection. In this study, we investigate patterns of genetic diversity in noncoding regions across the entire X chromosome of a global sample of 26 unrelated genetic females. We observe that genetic diversity in the PAR1 is significantly greater than the non-recombining regions (nonPARs). However, rather than an abrupt drop in diversity at the pseudoautosomal boundary, there is a gradual reduction in diversity from the recombining through the non-recombining region, suggesting that recombination between the human sex chromosomes spans across the currently defined pseudoautosomal boundary. In contrast, diversity in the PAR2 is not significantly elevated compared to the nonPAR, suggesting that recombination is not obligatory in the PAR2. Finally, diversity in the X-transposed region is higher than the surrounding nonPAR regions, providing evidence that recombination may occur with some frequency between the X and Y in the XTR.

scholarly journals Frequency of Cancer Genes on the Chicken Z Chromosome and Its Human Homologues: Implications for Sex Chromosome Evolution

2007 ◽  
Vol 2007 ◽  
pp. 1-8 ◽  
Author(s):  
Rami Stiglec ◽  
Matthias Kohn ◽  
James Fong ◽  
Tariq Ezaz ◽  
Horst Hameister ◽  
...  
Keyword(s):  
Sex Chromosomes ◽  
Chromosome Evolution ◽  
Sex Chromosome ◽  
Tumor Development ◽  
Single Copy ◽  
Z Chromosome ◽  
Cancer Genes ◽  
Database Analysis ◽  
Evolutionary Forces ◽  
Selection For

It has been suggested that there are special evolutionary forces that act on sex chromosomes. Hemizygosity of the X chromosome in male mammals has led to selection for male-advantage genes, and against genes posing extreme risks of tumor development. A similar bias against cancer genes should also apply to the Z chromosome that is present as a single copy in female birds. Using comparative database analysis, we found that there was no significant underrepresentation of cancer genes on the chicken Z, nor on the Z-orthologous regions of human chromosomes 5 and 9. This result does not support the hypothesis that genes involved in cancer are selected against on the sex chromosomes.

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