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3,458 results for “chromosomes”
Data from: Introgression of chromosome segments from multiple alien species in wheat breeding lines with wheat streak mosaic virus resistance
Pyramiding of alien-derived Wheat streak mosaic virus (WSMV) resistance and resistance enhancing genes in wheat is a cost-effective and environmentally safe strategy for disease control. PCR-based markers and cytogenetic analysis with genomic in situ hybridisation were applied to identify alien chromatin in four genetically diverse populations of wheat (Triticum aestivum) lines incorporating chromosome segments from Thinopyrum intermedium and Secale cereale (rye). Out of 20 experimental lines, 10 carried Th. intermedium chromatin as T4DL*4Ai#2S translocations, while, unexpectedly, 7 lines were positive for alien chromatin (Th. intermedium or rye) on chromosome 1B. The newly described rye 1RS chromatin, transmitted from early in the pedigree, was associated with enhanced WSMV resistance. Under field conditions, the 1RS chromatin alone showed some resistance, while together with the Th. intermedium 4Ai#2S offered superior resistance to that demonstrated by the known resistant cultivar Mace. Most alien wheat lines carry whole chromosome arms, and it is notable that these lines showed intra-arm recombination within the 1BS arm. The translocation breakpoints between 1BS and alien chromatin fell in three categories: (i) at or near to the centromere, (ii) intercalary between markers UL-Thin5 and Xgwm1130 and (iii) towards the telomere between Xgwm0911 and Xbarc194. Labelled genomic Th. intermedium DNA hybridised to the rye 1RS chromatin under high stringency conditions, indicating the presence of shared tandem repeats among the cereals. The novel small alien fragments may explain the difficulty in developing well-adapted lines carrying Wsm1 despite improved tolerance to the virus. The results will facilitate directed chromosome engineering producing agronomically desirable WSMV-resistant germplasm.
Data from: Multiple pairwise analysis of non-homologous centromere coupling reveals preferential chromosome size-dependent interactions and a role for bouquet formation in establishing the interaction pattern
During meiosis, chromosomes undergo a homology search in order to locate their homolog to form stable pairs and exchange genetic material. Early in prophase, chromosomes associate in mostly non-homologous pairs, tethered only at their centromeres. This phenomenon, conserved through higher eukaryotes, is termed centromere coupling in budding yeast. Both initiation of recombination and the presence of homologs are dispensable for centromere coupling (occurring in spo11 mutants and haploids induced to undergo meiosis) but the presence of the synaptonemal complex (SC) protein Zip1 is required. The nature and mechanism of coupling have yet to be elucidated. Here we present the first pairwise analysis of centromere coupling in an effort to uncover underlying rules that may exist within these non-homologous interactions. We designed a novel chromosome conformation capture (3C)-based assay to detect all possible interactions between non-homologous yeast centromeres during early meiosis. Using this variant of 3C-qPCR, we found a size-dependent interaction pattern, in which chromosomes assort preferentially with chromosomes of similar sizes, in haploid and diploid spo11 cells, but not in a coupling-defective mutant (spo11 zip1 haploid and diploid yeast). This pattern is also observed in wild-type diploids early in meiosis but disappears as meiosis progresses and homologous chromosomes pair. We found no evidence to support the notion that ancestral centromere homology plays a role in pattern establishment in S. cerevisiae post-genome duplication. Moreover, we found a role for the meiotic bouquet in establishing the size dependence of centromere coupling, as abolishing bouquet (using the bouquet-defective spo11 ndj1 mutant) reduces it. Coupling in spo11 ndj1 rather follows telomere clustering preferences. We propose that a chromosome size preference for centromere coupling helps establish efficient homolog recognition.
Data from: Genetic architecture of isolation between two species of Silene with sex chromosomes and Haldane's rule
Examination of the genetic architecture of hybrid breakdown can provide insight into the genetic mechanisms of commonly observed isolating phenomena such as Haldane's rule. We used line-cross analysis to dissect the genetic architecture of divergence between two plant species that exhibit Haldane's rule for male sterility and rarity, Silene latifolia and Silene diclinis. We made 15 types of crosses, including reciprocal F1, F2, backcrosses, and later-generation crosses, grew the seeds to flowering, and measured the number of viable ovules, proportion of viable pollen, and sex ratio. Typically, Haldane's rule for male rarity in XY animal hybrids is explained by interactions involving recessive X-linked alleles that are deleterious when hemizygous (dominance theory), while sterility is explained by rapid evolution of spermatogenesis genes (faster-male evolution). In contrast, we found that the genetic mechanisms underlying Haldane's rule between the two Silene species did not follow these conventions. Dominance theory was sufficient to explain male sterility, but male rarity likely involved faster-male evolution. We also found an effect of the neo-sex chromosomes of S. diclinis on the extreme rarity of some hybrid males. Our findings suggest that the genetic architecture of Haldane's rule in dioecious plants may differ from those commonly found in animals.
Data from: Chromosomal level reference genome of Tachypleus tridentatus provides insights into evolution and adaptation of horseshoe crabs
Horseshoe crabs including Tachypleus tridentatus are a group of marine arthropods living fossil species which have existed on the earth for 500 million years. However, the genetic mechanisms underlying their unique adaptive ability are still unclear. Here, we assembled the first chromosome-level T. tridentatus genome, and proofed that this genome is of very high quality with contig N50 1.69 Mb. By comparison with other arthropods, some gene families of T. tridentatus experienced significant expansion, whichare related to several signaling pathways, endonuclease activity, and metabolic processes. Based on the comparative analysis of genomics and 27 transcriptomes from 9 tissues, we found that the expanded Dscam genes usually locate at the key hub positions of immune network. Furthermore, the Dscam genes showed higher levels of expression in the yellow connective tissue, the birthplace of blood cells with strong differentiation capability, than the other 8 tissues. Besides, Dscam genes are positively correlated with the expression of the core immunity gene, clotting factor B, which is implicated in the coagulation cascade reaction. The effective and unusual immune ability endowed by the expansion and expression of Dscam genes in horseshoe crabs may be a factor that makes horseshoe crabs having a strong environmental adaptability with ~500 million years. The high-quality chromosome-level genome of a horseshoe crab and unique genomic features reported in this study provide important data resources for future studies on the evolutionary history of marine ecological systems.
Data from: De novo assembly of a chromosome-level reference genome of red spotted grouper (Epinephelus akaara) using nanopore sequencing and Hi-C
The red spotted grouper Epinephelus akaara (E. akaara) is one of the most economically important marine fish in China, Japan and Southeast Asia, and is a threatened species. The species is also considered a good model for studies of sex-inversion, development, genetic diversity and immunity. Despite its importance, molecular resources for E. akaara remain limited and no reference genome has been published to date. In this study, we constructed a chromosome-level reference genome of E. akaara by taking advantage of long-read single molecule sequencing and de novo assembly by Oxford Nanopore Technologies (ONT) and Hi-C. A red-spotted grouper genome of 1.135 Gb was assembled from a total of 106.29 Gb polished Nanopore sequence (GridION, ONT), equivalent to 96-fold genome coverage. The assembled genome represents 96.8% completeness (BUSCO) with a contig N50 length of 5.25 Mb and a longest contig of 25.75 Mb. The contigs were clustered and ordered onto 24 pseudo-chromosomes covering approximately 95.55% of the genome assembly with Hi-C data, with a scaffold N50 length of 46.03 Mb. The genome contained 43.02% repeat sequences and 5,480 non-coding RNAs. Furthermore, after mining several RNA-seq datasets, 23,809 (99.5%) genes were functionally annotated from a total of 23,924 predicted protein-coding sequences. The high-quality chromosome-level reference genome of E. akaara was assembled for the first time and will be a valuable resource for molecular breeding and functional genomics studies of red-spotted grouper in the future.
Data from: Sex-chromosome turnovers induced by deleterious mutation load
In sharp contrast with mammals and birds, many cold-blooded vertebrates present homomorphic sex chromosomes. Empirical evidence supports a role for frequent turnovers, which replace non-recombining sex chromosomes before they have time to decay. Three main mechanisms have been proposed for such turnovers, relying either on neutral processes, sex-ratio selection, or intrinsic benefits of the new sex-determining genes (due e.g. to linkage with sexually antagonistic mutations). Here we suggest an additional mechanism, arising from the load of deleterious mutations that accumulate on non-recombining sex chromosomes. In the absence of dosage compensation, this load should progressively lower survival rate in the heterogametic sex. Turnovers should occur when this cost outweighs the benefits gained from any sexually antagonistic genes carried by the non-recombining sex chromosome. We use individual-based simulations of a Muller's ratchet process to test this prediction, and investigate how the relevant parameters (effective population size, strength and dominance of deleterious mutations, size of non-recombining segment, and strength of sexually antagonistic selection) are expected to affect the rate of turnovers.
Data from: Speciation genomics and a role for the Z chromosome in the early stages of divergence between Mexican ducks and mallards
Speciation is a continuous and dynamic process, and studying organisms during the early stages of this process can aid in identifying speciation mechanisms. The mallard (Anas platyrhynchos) and Mexican duck (A. [p.] diazi) are two recently diverged taxa with a history of hybridization and controversial taxonomy. To understand their evolutionary history, we conducted genomic scans to characterize patterns of genetic diversity and divergence across the mitochondrial DNA (mtDNA) control region, 3523 autosomal loci and 172 Z-linked sex chromosome loci. Between the two taxa, Z-linked loci (ΦST = 0.088) were 5.2 times more differentiated than autosomal DNA (ΦST = 0.017) but comparable to mtDNA (ΦST = 0.092). This elevated Z differentiation deviated from neutral expectations inferred from simulated data that incorporated demographic history and differences in effective population sizes between marker types. Furthermore, 3% of Z-linked loci, compared to <0.1% of autosomal loci, were detected as outlier loci under divergent selection with elevated relative (ΦST) and absolute (dXY) estimates of divergence. In contrast, the ratio of Z-linked and autosomal differentiation among the seven Mexican duck sampling locations was close to 1:1 (ΦST = 0.018 for both markers). We conclude that between mallards and Mexican ducks, divergence at autosomal markers is largely neutral, whereas greater divergence on the Z chromosome (or some portions thereof) is likely the product of selection that has been important in speciation. Our results contribute to a growing body of literature indicating elevated divergence on the Z chromosome and its likely importance in avian speciation.
Data from: Getting a full dose? Reconsidering sex chromosome dosage compensation in the silkworm, Bombyx mori
Dosage compensation – equalizing gene expression levels in response to differences in gene dose or copy number – is classically considered to play a critical role in the evolution of heteromorphic sex chromosomes. As the X and Y diverge through degradation and gene loss on the Y (or the W in female-heterogametic ZW taxa), it is expected that dosage compensation will evolve to correct for sex-specific differences in gene dose. While this is observed in some organisms, recent genome-wide expression studies in other taxa have revealed striking exceptions. In particular, reports that both birds and the silkworm moth (Bombyx mori) lack dosage compensation have spurred speculation that this is the rule for all female-heterogametic taxa. Here we revisit the issue of dosage compensation in silkworm by replicating and extending the previous analysis. Contrary to previous reports, our efforts reveal that the global male:female expression ratio does not differ between the Z and autosomes, a pattern typically associated with dosage compensated taxa. We believe the previous report of unequal male:female ratios on the Z reflects artifacts of microarray normalization in conjunction with not testing a major assumption that the male:female global expression ratio was unbiased for autosomal loci. However, we also find that the global Z chromosome expression is significantly reduced relative to autosomes, a pattern not expected in dosage compensated taxa. This combination of male:female parity with an overall reduction in expression for sex-linked loci is not consistent with the prevailing evolutionary theory of sex chromosome evolution and dosage compensation.
Data from: Standing chromosomal variation in Lake Whitefish species pairs: the role of historical contingency and relevance for speciation
The role of chromosome changes in speciation remains a debated topic, although demographic conditions associated with divergence should promote their appearance. We tested a potential relationship between chromosome changes and speciation by studying two Lake Whitefish (Coregonus clupeaformis) lineages that recently colonized postglacial lakes following allopatry. A dwarf limnetic species evolved repeatedly from the normal benthic species, becoming reproductively isolated. Lake Whitefish hybrids experience mitotic and meiotic instability, which may result from structurally divergent chromosomes. Motivated by this observation, we test the hypothesis that chromosome organization differs between Lake Whitefish species pairs using cytogenetics. While chromosome and fundamental numbers are conserved between the species (2n = 80, NF = 98), we observe extensive polymorphism of subtle karyotype traits. We describe intrachromosomal differences associated with heterochromatin and repetitive DNA, and test for parallelism among three sympatric species pairs. Multivariate analyses support the hypothesis that differentiation at the level of subchromosomal markers mostly appeared during allopatry. Yet we find no evidence for parallelism between species pairs among lakes, consistent with colonization effect or postcolonization differentiation. The reported intrachromosomal polymorphisms do not appear to play a central role in driving adaptive divergence between normal and dwarf Lake Whitefish. We discuss how chromosomal differentiation in the Lake Whitefish system may contribute to the destabilization of mitotic and meiotic chromosome segregation in hybrids, as documented previously. The chromosome structures detected here are still difficult to sequence and assemble, demonstrating the value of cytogenetics as a complementary approach to understand the genomic bases of speciation.
Data from: A chromosome-level genome assembly of the Asian arowana, Scleropages formosus
Asian arowana (Scleropages formosus), an ancient teleost belonging to the Order Osteoglossomorpha, has been a valuable ornamental fish with some varieties. However, its biological studies and breeding germplasm have been remarkably limited by the lack of a reference genome. To solve these problems, here we report high-quality genome sequences of three common varieties of Asian arowana (the golden, red and green arowana). We firstly generated a chromosome-level genome assembly of the golden arowana, on basis of the genetic linkage map constructed with the restriction site-associated DNA sequencing (RAD-seq). In addition, we obtained draft genome assemblies of the red and green varieties. Finally, we annotated 22,016, 21,256 and 21,524 protein-coding genes in the genome assemblies of golden, red and green varieties respectively. Our data were deposited in publicly accessible repositories to promote biological research and molecular breeding of Asian arowana.
Data from: Linkage disequilibrium network analysis (LDna) gives a global view of chromosomal inversions, local adaptation and geographic structure
Recent advances in sequencing allow population-genomic data to be generated for virtually any species. However, approaches to analyse such data lag behind the ability to generate it, particularly in nonmodel species. Linkage disequilibrium (LD, the nonrandom association of alleles from different loci) is a highly sensitive indicator of many evolutionary phenomena including chromosomal inversions, local adaptation and geographical structure. Here, we present linkage disequilibrium network analysis (LDna), which accesses information on LD shared between multiple loci genomewide. In LD networks, vertices represent loci, and connections between vertices represent the LD between them. We analysed such networks in two test cases: a new restriction-site-associated DNA sequence (RAD-seq) data set for Anopheles baimaii, a Southeast Asian malaria vector; and a well-characterized single nucleotide polymorphism (SNP) data set from 21 three-spined stickleback individuals. In each case, we readily identified five distinct LD network clusters (single-outlier clusters, SOCs), each comprising many loci connected by high LD. In A. baimaii, further population-genetic analyses supported the inference that each SOC corresponds to a large inversion, consistent with previous cytological studies. For sticklebacks, we inferred that each SOC was associated with a distinct evolutionary phenomenon: two chromosomal inversions, local adaptation, population-demographic history and geographic structure. LDna is thus a useful exploratory tool, able to give a global overview of LD associated with diverse evolutionary phenomena and identify loci potentially involved. LDna does not require a linkage map or reference genome, so it is applicable to any population-genomic data set, making it especially valuable for nonmodel species.
Data from: Homologous sex chromosomes in three deeply divergent anuran species
Comparative genomic studies are revealing that, in sharp contrast with the strong stability found in birds and mammals, sex determination mechanisms are surprisingly labile in cold-blooded vertebrates, with frequent transitions between different pairs of sex chromosomes. It was recently suggested that, in context of this high turnover, some chromosome pairs might be more likely than others to be co-opted as sex chromosomes. Empirical support, however, is still very limited. Here we show that sex-linked markers from three highly divergent groups of anurans map to Xenopus tropicalis scaffold 1, a large part of which is homologous to the avian sex chromosome. Accordingly, the bird sex determination gene DMRT1, known to play a key role in sex differentiation across many animal lineages, is sex-linked in all three groups. Our data provide strong support for the idea that some chromosome pairs are more likely than others to be co-opted as sex chromosomes, because they harbor key genes from the sex determination pathway.
Chromosome-level genome assembly, annotation and evolutionary analysis of the ornamental plant Asparagus setaceus
<p><i>Asparagus setaceus </i>is a popular ornamental plant cultivated in tropical and subtropical regions globally. In this study, a chromosome-level reference genome of <i>A. setaceus</i> was constructed to assist in studying the genome structure and evolution. A total of 112.52 Gb of long reads was produced from Nanopore platform, resulting in 156.28× depth coverage of an estimated genome size of 720 Mb. The combination of Illumina-short reads, 10× Genomics linked reads, and Hi-C data produced the final chromosome quality genome of <i>A. setaceus</i> with a genome size of 710.15 Mb, accounting for 98.63% of the estimated genome size. Furthermore, 96.85% of the sequences were anchored to 10 super-scaffolds, corresponding to the 10 chromosomes. The genome of <i>A. setaceus</i> was predicted to have 28,410 genes, and 25,649 (90.28%) of these genes were functionally annotated. Genome annotation revealed that 65.59% were repetitive sequences, of which long terminal repeats were predominant (42.51% of the whole genome). Divergence between <i>A. setaceus</i> and its close relative <i>A. officinalis</i> is estimated to have occurred ~9.66 million years ago. Genome evolution analysis indicated that <i>A. setaceus</i> underwent two rounds of whole genome duplication events. In addition, 762 specific gene families, 898 expanded gene families, 96 positively selected genes, and 76 resistance R genes in <i>A. setaceus</i> were identified and functionally annotated. These findings provided insights into the structure and evolution of the <i>A. setaceus</i> genome and will facilitate the comparative genetic and genomic research on the genus <i>Asparagus</i>.</p>
Data from: Ancient chromosomal rearrangement associated with local adaptation of a post-glacially colonized population of Atlantic Cod in the northwest Atlantic
Intraspecific diversity is central to the management and conservation of exploited species, yet knowledge of how this diversity is distributed and maintained in the genome of many marine species is lacking. Recent advances in genomic analyses allow for genome-wide surveys of intraspecific diversity and offer new opportunities for exploring genomic patterns of divergence. Here, we analyzed genome-wide polymorphisms to measure genetic differentiation between an offshore migratory and a non-migratory population and to define conservation units of Atlantic Cod (Gadus morhua) in coastal Labrador. A total of 141 individuals, collected from offshore sites and from a coastal site within Gilbert Bay, Labrador, were genotyped using an ~11k single nucleotide polymorphism array. Analyses of population structure revealed strong genetic differentiation between migratory offshore cod and non-migratory Gilbert Bay cod. Genetic differentiation was elevated for loci within a chromosomal rearrangement found on linkage group 1 (LG1) that coincides with a previously found double inversion associated with migratory and non-migratory ecotype divergence of cod in the northeast Atlantic. This inverted region includes several genes potentially associated with adaptation to differences in salinity and temperature, as well as influencing migratory behaviour. Our work provides evidence that a chromosomal rearrangement on LG1 is associated with parallel patterns of divergence between migratory and non-migratory ecotypes on both sides of the Atlantic Ocean.
Data from: Large chromosomal rearrangements during a long-term evolution experiment with Escherichia coli
Large-scale rearrangements may be important in evolution because they can alter chromosome organization and gene expression in ways not possible through point mutations. In a long-term evolution experiment, twelve Escherichia coli populations have been propagated in a glucose-limited environment for over 25 years. We used whole-genome mapping (optical mapping) combined with genome sequencing and PCR analysis to identify the large-scale chromosomal rearrangements in clones from each population after 40,000 generations. A total of 110 rearrangement events were detected, including 82 deletions, 19 inversions, and 9 duplications, with lineages having between 5 and 20 events. In three populations, successive rearrangements impacted particular regions. In five populations, rearrangements affected over a third of the chromosome. Most rearrangements involved recombination between insertion sequence (IS) elements, illustrating their importance in mediating genome plasticity. Two lines of evidence suggest that at least some of these rearrangements conferred higher fitness. First, parallel changes were observed across the independent populations, with ~65% of the rearrangements affecting the same loci in at least two populations. For example, the ribose-utilization operon and the manB-cpsG region were deleted in 12 and 10 populations, respectively, suggesting positive selection, and this inference was previously confirmed for the former case. Second, optical maps from clones sampled over time from one population showed that most rearrangements occurred early in the experiment, when fitness was increasing most rapidly. However, some rearrangements likely occur at high frequency and may have simply hitchhiked to fixation. In any case, large-scale rearrangements clearly influenced genomic evolution in these populations.
Data from: Introgression maintains the genetic integrity of the sex-determining chromosome of the fungus Neurospora tetrasperma
Genome evolution is driven by a complex interplay of factors, including selection, recombination, and introgression. The regions determining sexual identity are particularly dynamic parts of eukaryotic genomes that are prone to molecular degeneration associated with suppressed recombination. In the fungus Neurospora tetrasperma, it has been proposed that this molecular degeneration is counteracted by the introgression of non-degenerated DNA from closely related species. In this study, we used comparative and population genomic analyses of variation among 92 genomes from eight phylogenetically and reproductively isolated lineages of N. tetrasperma, and its three closest relatives, to investigate the factors shaping the evolutionary history of the genomes. We found that suppressed recombination extends across at least 6 Mbp (~63%) of the mating-type (mat) chromosome in N. tetrasperma, and is associated with decreased genetic diversity, which is likely the result primarily of selection at linked sites. Furthermore, analyses of molecular evolution revealed an increased mutational load in this region, relative to recombining regions. However, comparative genomic and phylogenetic analyses indicate that the mat chromosomes are temporarily regenerated via introgression from sister species; six out of eight lineages show introgression into one of their mat chromosomes, with at least three other Neurospora species acting as donors. The introgressed tracts have been driven to fixation in lineages, suggesting that they confer an adaptive advantage in natural populations, and our analyses support the presence of selective sweeps in at least one of the lineages. Thus, these data strongly support the previously hypothesized role of introgression as a mechanism for the maintenance of mating-type determining chromosomal regions.
FIGURES 1–2. Endecous ubajarensis n in A new species of Endecous Saussure, 1878 (Orthoptera, Gryllidae) from northeast Brazil with the first X X 0 chromosomal sex system in Gryllidae
FIGURES 1–2. Endecous ubajarensis n. sp. habitus. 1—holotype male; 2—paratype female UBA02.
FIGURE 14 in A new species, Simulium (Nevermannia) berchtesgadense (Diptera: Simuliidae), and its chromosomes, from the Alps of southeastern Germany
FIGURE 14. Simulium (Nevermannia) berchtesgadense, larva: mandible (objective magnification: 40 x).
FIGURE 1 in A new species, Simulium (Nevermannia) berchtesgadense (Diptera: Simuliidae), and its chromosomes, from the Alps of southeastern Germany
FIGURE 1. Simulium (Nevermannia) berchtesgadense, male: hind leg (objective magnification: 10 x).
FIGURES 21–22 in A new species of Miogryllus Saussure, 1877 and new record of Miogryllus piracicabensis Piza, 1960 (Orthoptera: Gryllidae) from State of Rio Grande do Sul, Brazil, with calling song and chromosome complement
FIGURES 21–22. Habitus of Miogryllus piracicabensis Piza, 1960 in vivo. 1—male, 2—female.
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These curated guides explain access requirements, typical timelines, costs, and reuse considerations for widely used research datasets.
Allen Brain Atlas
Allen Brain Atlas is an Allen Institute collection of brain map atlases, datasets, APIs, and analysis tools covering mouse, human, and non-human primate brain resources.
Annotated Behaviour and Observability Dataset (ABODe)
ABODe is a University of Edinburgh DataShare dataset for behavior classification in group-housed mice using home-cage video, identities, bounding boxes, ground-plate positions, and annotator labels.
DANDI Archive for NWB datasets
DANDI is a BRAIN Initiative archive for publishing and sharing neurophysiology data, including electrophysiology, optophysiology, and behavioral data packaged as NWB and related standards.
International Brain Laboratory public data
The International Brain Laboratory public data releases expose standardized mouse decision-making experiments, including Neuropixels recordings, widefield calcium imaging, behavior, and session metadata accessed through the ONE API.
OpenNeuro
OpenNeuro is a free, open platform for sharing neuroimaging datasets, with public search, dataset pages, and download paths for web, S3, DataLad, and the OpenNeuro CLI.