Agricultural and Biological Sciences · Research topic

Open research questions in Chromosomal and Genetic Variations

56 unresolved questions extracted from the limitations and future-work sections of 360 Chromosomal and Genetic Variations papers in our library. Each links back to the study that raised it.

What the literature leaves open

  • SignificanceThree-dimensional genome architecture strongly influences gene regulation, yet little is known about 3D genome architecture in an organismal group that has adapted to nearly all ecosystems on our planet, Fungi.

    Comparative analyses reveal rapid turnover and emergence of transitory 3D genome architectures in the fungal kingdom · 2026 · DOI
  • Although the DNA composition of the GRC, as well as elimination processes during spermatogenesis and early embryogenesis, have been characterised previously, little is known about the cytogenetic features underlying its unusual behaviour, including its stable transmission through the maternal germline.

    Evidence of two centromeres in the germline-restricted chromosome (GRC): insights from zebra finch lampbrush chromosomes · 2026 · DOI
  • Among these, hERV-K (HML-2) remains the most recently active family and its dysregulation is strongly associated with diverse cancers and neurodegenerative pathologies, yet the structural basis of its integration remains poorly understood.

    Structural characterization of human endogenous retrovirus integration and strand transfer inhibition · 2026 · DOI
  • The sperm killer Segregation Distorter (SD) in Drosophila melanogaster is a well-studied driver but like most complex drivers its mechanism remains elusive.

    Disruption of small RNAs and mechanistic variation in Segregation Distorter, a sperm-killing drive system in Drosophila melanogaster · 2026 · DOI
  • Polyploidy is now understood to drive significant shifts in gene content and cis-regulatory variation, both of which are fundamental to plant stress resilience. Gene content variation, including the gain or loss of specific genes, directly impacts metabolic and signaling pathways vital for adapting to environmental challenges. Simultaneously, changes in CREs lead to diverse and novel patterns of gene activity that fine-tune stress responses. This dynamic interplay between genetic and regulatory changes contributes to the expanded phenotypic diversity and enhanced adaptive capabilities that enable polyploids to thrive under challenging conditions. A comprehensive understanding of regulatory variation in polyploids holds immense potential for developing nextgeneration, climate-resilient crops and ensuring global food security. While the added phenotypic diversity, genetic Fig. 4. HE and its impact on gene dosage and structure. This figure illustrates how HEs, which are recombination events between chromosomes from different diploid progenitors (shown in blue and yellow), can alter gene dosage and create novel gene structures in a polyploid genome. Panel (A) depicts the potential outcomes of HE on homoeolog dosage. A newly formed tetraploid begins with two copies from each parental genome (Left). HEs and subsequent segregation can alter this ratio to 3:1 or 1:3 (Middle) and, in extreme cases, to 4:0 or 0:4 (Right). Panel (B) shows that HEs can also occur within a gene. These events can either alter CRE variants associated with a gene (Left to Middle) or, in more extreme cases, create chimeric versions of genes consisting of exons from both homoeologs (Middle to Right). 8 of 10 https://doi.org/10.1073/pnas.2522064123 pnas.org redundancy, and multiple gene variants in polyploids provide a rich substrate for adaptation, they have historically made it difficult to apply molecular breeding approaches. For this reason, some breeding communities have opted to work with diploid progenitors, sacrificing valuable phenotypic diversity for the simplicity and lower cost of genetic markers. The advent of new genotyping and bioinformatic tools, combined with the development of haplotype-phased pangenomes, is making the use of molecular breeding tools with polyploids increasingly more accessible and affordable for a broader range of communities working on a wide variety of polyploid crops. While significant progress has been made in understanding gene and CRE evolution following polyploidy, many aspects remain poorly understood. It is likely that insights into stress adaptations and resilience are likely to derive from these five key research areas. 1 Dissecting Regulatory Complexes: Understanding which CREs function together to regulate a single gene is a major challenge.

    Genome evolution through polyploidy: Enhancing plant stress resilience in agriculture · 2026 · DOI
  • OPEN ACCESS Genome evolution through polyploidy: Enhancing plant stress resilience in agriculture Patrick P. Edgera,b,c,1, Melanie J. A. Bodya, Sonia De Donnoc, Adrian E. Plattsa, Jianrong Wangd, and Jiming Jianga,e Edited by Donald Fox, Duke University, Durham, NC; received September 1, 2025; accepted December 16, 2025 by Editorial Board Member James A. Birchler Polyploidy, also known as whole genome duplication, is a major evolutionary force in plants, driving diversification and the generation of novel phenotypic variation, including superior abiotic and biotic stress tolerance. The enhanced stress resilience observed in certain polyploids is hypo­ thesized to arise from dynamic epigenetic and genetic changes, including variations in gene content and cisregulatory elements (CREs), that emerge following poly­ ploidization. These changes directly impact various regulatory, signaling, and metabolic pathways associated with stress response and adaptation. Within polyploid populations, processes like gene duplications, fractionation, and homoeologous exchanges actively shape novel gene content variation, while, simultaneously, alterations in CREs (DNA sequences controlling gene expression) lead to diverse regulatory patterns. This dynamic interplay between changes in gene content and regulation further contributes to expanded phenotypic variation, including enhanced stress resilience. We discuss how advanced genomic and epigenomic techniques, such as pangenomics and single-cell assay for transposase-accessible chromatin with sequencing, are used to uncover these variations and outline new bioinformatic approaches to reveal the underlying genetics of stress resilience and adaptation. Finally, we summarize what remains poorly understood to guide future research, with the goal of unlocking the full potential for enhancing resilience in polyploid crops. polyploidy | stress resilience | genome evolution | agriculture | whole genome duplication Global agricultural productivity faces an unprecedented challenge from the increasing frequency and intensity of various abiotic and biotic stresses (1). Abiotic stressors, such as extreme temperatures, drought, flooding, and salinity, are directly exacerbated by shifting global weather patterns, which severely impacts crop yields worldwide (2). Simul­ taneously, biotic stresses, including novel pest outbreaks and disease epidemics, are also influenced by changing environmental conditions, further threatening food production (3). This complex interplay of escalating stresses necessitates the urgent development and deployment of superior climateresilient crops to ensure global food security for a growing population (4).

    Genome evolution through polyploidy: Enhancing plant stress resilience in agriculture · 2026 · DOI
  • In this perspective, we have highlighted diverse stresses that generate polyploidy. Within this diversity, it is intriguing that similar stresses can generate polyploidy in very different organisms and tissues, both in normal and diseased settings. The emerging theme is that each stress impedes cell division whether through inhibiting M phase of the cell cycle, causing DNA damage and triggering a checkpoint, affecting the spindle and chromosome segregation, or preventing cytokinesis, which all cause the cell to double its DNA content. Further, regardless of organism or stress, there are common impacts of stress-induced ploidy changes on the very different biological scales of genomes, cells, tissues, and organisms. The consequences of the ploidy change can be positive, negative, or neutral in withstanding the stress and in the ongoing life of the organism. Comparison across organisms has been instrumental in uncovering the overarching principles of polyploidy from the specifics of the organism and situation. We suggest that further integration of data from different polyploid cells and organisms is an important avenue for future advances in our understanding of how polyploidy creates multiscale effects from genomes to cells to tissues and organisms. Yet, context-specific differences remain, and these differences are important in understanding the impact of a given stress on polyploidy in that setting. A common misconception of polyploidy is that it is a rare event—yet the study of organisms under stress already demonstrates that polyploidy is very common and a major player in a myriad of life’s processes. This recognition of the prevalence and functional role of polyploidy is likely only to increase. While quite a bit is understood about how stresses cause polyploidy, less is known about the consequences. Future work should focus on the grand challenges of 1) further elucidating the mechanisms through which merely doubling (or multiplying) the DNA content changes the cell; 2) how these cellular effects propagate to the tissue and organism scales; and 3) how the consequences of polyploidy affect the organism’s resilience to stress. Data, Materials, and Software Availability. There are no data underlying this work. ACKNOWLEDGMENTS. We thank Jeffrey Doyle for insightful comments on the manuscript. We apologize to those whose work we could not cite due to space limitations. The authors’ research is supported by NSF Grant DBI-2320251. LSO is supported by NSF Graduate Research Fellowship DGE-2139899. We thank the Polyploidy Integration and Innovation Institute (https://www.pi3biology. org/) for thoughtful discussions. J. P. Morris, T. Baslan, D. E. Soltis, P. S. Soltis, D. T. Fox, Integrating the study of polyploidy across organisms, tissues, and disease. Annu. Rev. Genet. 58, 297–318 (2024). V. P. Losick, D. T. Fox, A. C.

    Growth under pressure: The pros and cons of polyploidy induced by stress · 2026 · DOI
  • OPEN ACCESS Growth under pressure: The pros and cons of polyploidy induced by stress Lilijana Sarabia Olivera,b,1, Paulo B. Belatoa,c,1, Joshua Silvaa,c,1, Anna Selmeckia,d, Donald T. Foxa,c, and Adrienne H. K. Roedera,b,2 Edited by James Birchler, University of Missouri, Columbia, MO; received September 15, 2025; accepted December 11, 2025 In native environments, organisms are faced with an array of acute or chronic stresses. These stresses include toxins, pathogens, and physical injury. An increasingly recognized response to diverse stresses is whole genome doubling or polyploidy. This transformative cellular property alters genome integrity, cellular structure, and tissue architecture. Whether polyploidy is a positive, negative, or neutral outcome of a stress is a current topic of investigation in numerous contexts including during fungal infection of plants and animals, during regeneration of wounded tissues, and in human diseases such as cancer. In this review, we highlight the wide range of stresses that promote polyploidy in fungal, plant, and animal contexts. Specifically, we highlight major mechanisms that lead to stress-induced polyploidy within somatic or germline tissues through alteration of the cell cycle. We discuss the impact of such stress-induced polyploidy on genomes, cells, and tissues and emphasize commonalities across organisms and biological scales. A common theme that has emerged is that polyploidy facilitates numerous subsequent genomic and cellular changes following abrupt stresses, and these changes can impact tissue architecture and function. polyploidy | endocycles | oxidative stress | genome instability | stress Polyploidy, or whole genome duplication, is a transformative cellular process associated with increased cell size (1–3). Polyploidization can occur at the somatic or germline level, resulting in endopolyploid cells or entirely polyploid organisms, respectively (3). While polyploidy is often a normal product of many developmental processes, in recent years it has become clear that polyploidy frequently results from a variety of stress conditions (3–5). Such instances of polyploidy have previously been studied in disparate biological contexts, although common themes across diverse disciplines such as agriculture and medicine are emerging (5, 6). As a result, there is currently a significant interest in characterizing how external stresses can promote increased occurrence of polyploidy, and the resulting impacts on genomes, cells, tissues, and organisms. In many stress-related contexts, polyploidy provides a benefit, whereas in others it may exacerbate the stress. Additionally, there are many examples of stress-induced polyploidy for which we do not know the impact. This perspective highlights distinct stresses that promote polyploidy in fungi, plants, and animals. Herein, we broadly define “stress” as an acute change in an organism’s environmental conditions, either biotic or abiotic, and including physical or chemical effects experimentally inflicted upon an organism. Our focus here is on polyploidy that arises upon stress within cells or tissues, and/or through alteration of the mitotic cell cycle. Specifically, incomplete mitotic cell cycles with continued cycles of S-phase can produce polyploid somatic cells, termed endopolyploidy if occurring in multicellular organisms (Fig. 1). Such cycles can omit cytokinesis, anaphase, or M-phase altogether (Fig. 1). For the impact of other related topics, such as stress-induced polyploidy through cell fusion or stress-induced organismal polyploidy, we refer the reader to other excellent reviews (5, 7–10). In this perspective, we first present an overview of numerous stresses that are connected to polyploidy, and the routes by which such stresses generate whole genome doubling. Subsequently, we discuss both the advantageous and detrimental consequences of polyploidy on genomes, cells, and tissues when it is known. Finally, we discuss areas for future focus. 1.

    Growth under pressure: The pros and cons of polyploidy induced by stress · 2026 · DOI
  • OPEN ACCESS Polyploidy: A macromutational force pushing bioeconomic developments Marlies K. R. Peetersa,b,1 and Yves Van de Peera,c,d,e,1 Edited by James A. Birchler, University of Missouri, Columbia, MO; received September 14, 2025; accepted February 24, 2026 Polyploidization, the consequence of genome doubling, is a macromutation that reshapes genomes, phenotypes, and ecological interactions. Polyploidization often results in novel phenotypes, including alterations in size, physiology, biochemistry, and enhanced stress tolerance. Here, we discuss how strategically leveraging polyploidy can provide significant advancements within the modern bioeconomy committed to reducing our ecological footprint through the sustainable production and use of biological resources. The bioeconomy spans diverse sectors, including agriculture, health sciences, and biotechnology. By elucidating and leveraging the im­ mediate, or short-term, effects of polyploidization, such as harnessing genetic diversity, extensive biomass production, diversification of metabolites, and improved stress resilience, we highlight how this process unlocks vast, underexplored bioeconomic opportunities. This includes accelerating the exploration of new breeding techniques, speeding up the domestication of new local varieties or medicinal plants, and offering possibilities for improved biofuel production, bioremediation strategies, therapies, and production and discovery of bioactive compounds. The multilayered effects of polyploidization shared across sectors can foster inter­ disciplinary exchange and are essential for advancing toward a more sustainable bioeconomy. bioeconomy | genetic diversity | adaptability | metabolic capacity | morphological changes Whole-genome duplication (WGD), leading to polyploidy, is a widespread phenomenon that has been studied for over 100 y (1). Polyploidy can occur naturally or can be induced, affecting cells, tissues, or entire organisms. Although poly- ploidy is often detrimental due to genomic instability, mitotic and meiotic abnormalities, and minority cytotype exclusion (2), polyploid organisms exist everywhere, but particularly in plants (3, 4). Ancient polyploidy events coin- cide with the origin and diversification of major phyloge- netic lineages, including vertebrates, fishes, and flowering plants, and within flowering plants, core eudicots, mono- cots, orchids, grasses, composites, and legumes (5), sug- gesting a role for WGD in phenotypic diversity, with a subsequent facilitating role in speciation (6, 7). Moreso, ancient polyploidy events seem to correlate with periods of climate change (8). Polyploidization is frequently associated with novel phe- notypes. Doubling the DNA content can shift gene expres- sion, metabolism, and epigenetic modelling, with major consequences for development and physiological responses (Box 1) (9–11). These polyploidy-linked responses have long been exploited in agriculture, because of their desirable agronomic value, such as enhanced size and stress toler- ance, resulting in more productive and sustainable crop varieties. Although most polyploidy applications so far have been framed within the so-called green biotechnology and bioeconomy, we here describe how short-term effects of polyploidization are increasingly exploited across blue, white, and red bioeconomies (Box 2, Fig. 1, and SI Appendix, Fig. S1). A modern and sustainable bioeconomy is widely viewed as a route to address climate change, insufficient food pro- duction, pollution and polluting energy generation, and biodiversity loss (12). This transition from fossil-based to bio-based products and energy aims to support a carbon- low society, sustainable food production, and bio-based resources for materials, energy, and services. Because it spans sectors from agriculture, ecology, and forestry, to waste management, bioenergy and biofuels, pharmaceuti- cals and health care, the bioeconomy has a central role to reach the sustainability goals postulated in 2015 in the European Green deal, aiming to transition into a cleaner, healthier, and more resource-efficient economy while pro- tecting ecosystems and addressing social and regional inequalities (12, 13). Here, we summarize applications by illustrating selected examples in which polyploidization lev- erages the goals of climate neutrality, investment in renew- able energy, circular economy, ecosystems, and pollution reduction (Box 3 and Fig. 2).

    Polyploidy: A macromutational force pushing bioeconomic developments · 2026 · DOI
  • The integration of speed breeding, genomic selection (GS), and precision genome editing provides a promising framework for accelerating diploid hybrid potato breeding, all of which depend on the prior establishment of self-compatibility. Speed breeding shortens generation cycles by optimizing growth conditions, enabling more rapid generation advancement of SC materials. Genomic selection supports early and high-throughput prediction of complex traits, allowing more efficient screening of SC lines and promising hybrid combinations. When combined with targeted editing of SI-related genes, these tools can help streamline breeding pipelines; however, efficiency varies across genetic backgrounds, and long-term field performance remains to be fully validated (Xu et al., 2022). 4.4 Alternative reproductive strategies: apomixis Apomixis is an asexual reproductive system that produces clonal seeds without fertilization, representing an alternative reproductive strategy that reduces dependence on sexual reproduction and selfing rather than directly overcoming SI. Apomixis does not Future research directions toward diploid hybrid potato breeding should be rooted in a deeper understanding of SI mechanisms and the rational application of SC-related technologies. To achieve stable and efficient diploid hybrid breeding systems, research priorities should be balanced between practically achievable shortterm goals and longer-term exploratory objectives. In the short term, core efforts should focus on strengthening the efficiency and stability of SC induction systems mediated by Sli introgression and genome editing. It is critical to recognize that Slimediated SC is not universally effective across all genetic backgrounds, and its function may be modulated by additional genetic modifiers and environmental factors. This limitation is consistent with the variable performance of Sli-based SC observed in earlier germplasm evaluation and breeding application sections. Further characterization of these regulatory interactions will help improve the robustness and predictability of SC conversion in diverse elite germplasm. Additional short-term priorities include optimizing breeding pipelines for inbred line development, mitigating inbreeding depression and deleterious genetic load, and improving the reliability of phenotypic screening for SC traits.

    Breaking self-incompatibility for diploid hybrid potato breeding: advances, mechanisms, and emerging technologies · 2026 · DOI
  • The K-mer analysis (K=27) was used to evaluate completeness of MIC and MAC assemblies for 7 P. aurelia species, but the paper does not specify the reference genome size estimates used for calculating assembly completeness percentages, or whether different K-mer sizes were evaluated to optimize detection of repetitive Helitron sequences in germline chromosomes.

    The tiny germline chromosomes of Paramecium aurelia have an exceptionally high recombination rate and are capped by a new class of Helitrons · 2026 · DOI
  • Synteny between MAC and MIC sequences was manually curated using Circos visualization of nucmer alignments, but no systematic quality metrics or error rates are reported for this curation process, and no inter-curator agreement assessment was conducted across the 7 P. aurelia species MAC/MIC genome pairs.

    The tiny germline chromosomes of Paramecium aurelia have an exceptionally high recombination rate and are capped by a new class of Helitrons · 2026 · DOI
  • The dN/dS computation for full-size Helitron transposase copies in P. aurelia was initiated (phyML phylogenetic tree, MAFFT L-INS-i alignment), but the methods section ends abruptly without reporting the actual dN/dS values, selection pressure estimates, or comparison of transposase evolution rates across the 7 Paramecium species.

    The tiny germline chromosomes of Paramecium aurelia have an exceptionally high recombination rate and are capped by a new class of Helitrons · 2026 · DOI
  • Helitron identification and manual curation was performed only on Illumina assemblies of the MIC genomes; the paper does not address whether long-read sequencing (PacBio, Oxford Nanopore) would resolve Helitron structure, copy number variation, and terminal inverted repeat sequences more accurately across the 7 P. aurelia species.

    The tiny germline chromosomes of Paramecium aurelia have an exceptionally high recombination rate and are capped by a new class of Helitrons · 2026 · DOI
  • Gene annotation of MIC-limited regions in P. aurelia was performed using EuGene with filters for length ≥100 nt and GC content <50%, but the paper does not characterize whether MIC-specific genes have distinct codon usage patterns, regulatory sequences, or functional categories that warrant different annotation parameters compared to MAC-destined genes.

    The tiny germline chromosomes of Paramecium aurelia have an exceptionally high recombination rate and are capped by a new class of Helitrons · 2026 · DOI
  • The OES (Other Eliminated Regions) compartment in the P. tetraurelia EZL1 assembly was subdivided into PGM-dependent and PGM-independent sub-compartments using coverage thresholds (≥5X), but no validation is provided confirming that these threshold values accurately distinguish functionally distinct elimination pathways in P. aurelia germline DNA.

    The tiny germline chromosomes of Paramecium aurelia have an exceptionally high recombination rate and are capped by a new class of Helitrons · 2026 · DOI
  • The telomere junction analysis identified redundancy in telomere repeat clusters where internal junctions and edge junctions mapped to the same location, and antisense-oriented clusters mapped to identical positions. The paper does not specify a computational method to definitively resolve or distinguish these redundant MIC telomeric junctions in P. aurelia germline chromosomes.

    The tiny germline chromosomes of Paramecium aurelia have an exceptionally high recombination rate and are capped by a new class of Helitrons · 2026 · DOI
  • Most centromeric repeats identified in perennial soybeans were retrotransposons with only one type of tandem repeat found in the FF genome, which might be attributed to incomplete assemblies of perennial genomes, especially centromeric regions.

    Centromere evolution in annual and perennial soybeans and its implication for hybridization in cultivated species · 2026 · DOI
  • Our study has limitations that should be acknowledged. Assembly of the JET transcriptome can lead to incomplete annotations. Although these issues are minimized at the ORF level, they impact the interpretation of our results. Second, JET-ORF functions are probably context dependent. Our observations were made under steady-state conditions in a specific cell line, and it remains unclear how these processes might vary under different stimuli. For example, although HTT-JET-KO cells grow slower, only one gene was differentially expressed compared with WT cells. Cell cycle synchronization would probably reveal other transcriptomic differences related to proliferation. Tissue-dependent expression of JETs suggests that the observed sub-functionalization is environment-dependent. Variability between cell lines and single-cell clones can also impact the results. Future studies incorporating long-read sequencing and a variety of biological contexts (reflecting tissue environment) will be required to fully understand the functional aspects of JET-ORF diversity and selection pressures.

    Transposable element exonization generates a reservoir of evolving and functional protein isoforms · 2024 · DOI
  • As abnormal blastomeres may have the potential to be eliminated during the early cleavage stages, the ultimate impact of ICE on embryo health remains unclear.

    WORLD OF REPRODUCTIVE BIOLOGY: The Wide Reach of Chromosome Rearrangements · 2012 · DOI
  • In species where they are present, retrozyme copy number, consensus length, and monomer proportion vary widely across species and retrozyme families, suggesting diverse amplification dynamics.

    Animal retrozymes are nonautonomous sequences of Penelope-like elements · 2026 · DOI
  • While many recent lepidopteran genome assemblies contain W chromosome scaffolds, the accuracy and consistency of these assemblies remain uncertain, due to lack of replication within species.

    Wrong but useful: Bombyx silkworm W chromosome assemblies are flawed but still capture strongly reduced diversity of repetitive DNA · 2026 · DOI
  • The factors driving the evolution of genome architectures have primarily been assessed in animals and plants, yet large parts of the tree of life remain poorly explored.

    Comparative analyses reveal rapid turnover and emergence of transitory 3D genome architectures in the fungal kingdom · 2026 · DOI
  • Genome evolution in eukaryotes is predominantly driven by the dynamics of repetitive sequences, which vary widely in both copy number and sequence composition.

    The genetic control of rapid genome content divergence in Arabidopsis thaliana · 2026 · DOI
  • Heterostyly has been lost multiple times independently across the flax genus, leading to homostyly and self-compatibility, but the genetic causes of this transition are not fully understood.

    Chromosome-scale Genome Assembly of Lewis Flax (Linum lewisii Pursh.) · 2026 · DOI

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