Karyotypic Variation Research Articles

Characterization of Razi Bovine Kidney (RBK) Cell Line as a Sensitive Cell to Bovine Herpesvirus-1 (BoHV-1).

Viruses are obligate parasites that completely rely on host cells for survival and replication. Razi Bovine Kidney (RBK) cell line was introduced and developed by the Razi Vaccine and Serum Research Institute. It has been successfully established as a continuous cell line over successive passages. As demonstrated in this experimental study, the RBK cells have shown suitable sensitivity to certain viruses, including Bovine Herpesvirus-1 (BoHV-1) virus. In the present research, the RBK cell line characteristics were analyzed using molecular and karyotype methods and growth specifications. Cloning of the RBK cell line was performed using the limited dilution method, and each cell clone was quantitatively and qualitatively characterized. Four cell clones were compared based on their sensitivity to the BoHV-1 virus. Then, the RBK-D5 clone was selected as the most appropriate cell line for further studies. The RBK-D5 was subjected to tests for identity, chromosomal analysis, and doubling time. In the end, the origin of this cell line was confirmed by the PCR method. It was observed that the cell line exhibited karyotype diversity due to aneuploidy, which can be responsible for the procreation of chromosomal instability. This diversity represents chromosomal changes in the continuous cell line that carries the characteristic of an immortalized cell line. The RBK-D5 was found to be more sensitive to the BOHV-1 virus. Surprisingly, its titer was evaluated at 108.5 CCID50/ml. The obtained results suggested that the RBK cell line is suitable for the BoHV-1 virus and can be useful for virus detection, propagation, and quality control or viral titration.

Incidence and frequency of desynapsis in Eremurus persicus (Jaub. & Spach) Boiss.(Asphodelaceae) – A native and important medicinal plant species of Western Himalaya

Eremurus persicus (Jaub. & Spach) Boiss. (Asphodelaceae); a little known species of genus Eremurus grows in arid and semi-arid regions, on rocky mountains in Central Asia and Middle East. The species is native and an important medicinal plant used to treat various diseases. In the current study, we examined male meiosis, karyotypic variability, pollen viability and reproductive output of three populations of the target species. All the studied populations have diploid chromosome count of 2n = 2x =14. Meiotic course in majority of the pollen mother cells (PMCs) in all the three populations is not normal due to the presence of desynapsis at diplotene and metaphase-I. Instead of 7IIs most of the PMCs examined reveal varying number of bivalents and univalents. Anaphasic segregation is also affected in few PMCs. Present study also revealed that the species has asymmetric karyotype of 10 long and 4 short chromosomes. Species exhibits fruit abortion that results in extremely low fruit/seed set. The meiotic abnormalities and low fruit/seed set may be attributed to restricted distribution of this important plant species. Present study may prove helpful in devising the conservation and management strategies for this prized plant species.

Cytogenetic Study of Five Varieties of Callisia repens (Jacq.) L. (Commelinaceae) from Laos

Cytogenetical studies were carried out on five varieties of Callisia repens, i.e., turtle vine, green, pink lady, gold, and Bianca. The morphological characteristics of all five varieties differed in leaf shape and color of the plant. All five varieties have the same chromosome number, 2n = 12, and the fundamental number (NF) = 24. The number of metacentric (m), submetacentric (sm), and subtelocentric (st) chromosomes was related to the discrepancies between the various karyotypes that were found. The formula for each of the karyotypes was 2m + 2sm + 8st (turtle vine), 2m + 10st (green), 8m + 4st 14 (pink lady), 2m + 4sm + 6st (gold), and 2m + 2sm + 8st (Bianca). Therefore, all five strains had asymmetrical karyotypes. The chromosome number of C. repens has been reported previously, but this is the first report of karyotype variation among the varieties. Furthermore, principal component analysis (PCA) of the karyotype formula was able to distinguish C. repens ‘pink lady’, C. repens ‘green’, and C. repens ‘gold’, but it was unable to differentiate between C. repens ‘Bianca’ and C. repens ‘turtle vine’. Additionally, PCA conducted on the centromeric index (CI) and the leaf colors of the five varieties of C. repens successfully separated all of them. Therefore, the prominent morphological traits and karyotype information of the five varieties of C. repens from Laos can be used to distinguish between them.

Mechanisms of Karyotypic Diversification in Ancistrus (Siluriformes, Loricariidae): Inferences from Repetitive Sequence Analysis.

Ancistrus is a highly diverse neotropical fish genus that exhibits extensive chromosomal variability, encompassing karyotypic morphology, diploid chromosome number (2n = 34-54), and the evolution of various types of sex chromosome systems. Robertsonian rearrangements related to unstable chromosomal sites are here described. Here, the karyotypes of two Ancistrus species were comparatively analyzed using classical cytogenetic techniques, in addition to isolation, cloning, sequencing, molecular characterization, and fluorescence in situ hybridization of repetitive sequences (i.e., 18S and 5S rDNA; U1, U2, and U5 snDNA; and telomere sequences). The species analyzed here have different karyotypes: Ancistrus sp. 1 (2n = 38, XX/XY) and Ancistrus cirrhosus (2n = 34, no heteromorphic sex chromosomes). Comparative mapping showed different organizations for the analyzed repetitive sequences: 18S and U1 sequences occurred in a single site in all populations of the analyzed species, while 5S and U2 sequences could occur in single or multiple sites. A sequencing analysis confirmed the identities of the U1, U2, and U5 snDNA sequences. Additionally, a syntenic condition for U2-U5 snDNA was found in Ancistrus. In a comparative analysis, the sequences of rDNA and U snDNA showed inter- and intraspecific chromosomal diversification. The occurrence of Robertsonian rearrangements and other dispersal mechanisms of repetitive sequences are discussed.

Karyotypes of 10 Anuran Species from the Qinghai–Tibetan Plateau

The Qinghai–Tibet Plateau (QTP) is the highest and largest mountain plateau in the world, which has become a focus area of amphibian biodiversity research and conservation, depending on its large number of endemic and threatened species. Among the 58 families of Anura, only a few species of four families (Megophryidae, Bufonidae, Dicroglossidae, Ranidae) are distributed in QTP. Revealing the genetic diversity of these species is crucial for research on their environmental adaptability and biodiversity conservation. Chromosome rearrangements are a critical source of genetic variation, which is recognized as a driver of speciation, providing the genetic material for differentiation and environmental adaptation of amphibians. Here, we identified the karyotypes of 10 species of the above families from the QTP. The karyotypes of these species were obtained from new sites that were not previously reported. Among them, the karyotypes of D. himalayanus and tetraploid B. zamdaensis were reported for the first time. In particular, the ploidy of B. zamdaensis from Zanda, China, was found to be distinctly different from the ploidy from Spiti River, India. This indicates that they have presented species differentiation and supports the multiple and complicated polyploidization events in the Bufotes toads. Furthermore, the different locations of the secondary constriction between the Weixi and Zhongdian populations of O. xiangchengensis support that there is a karyotypic variation between the two subspecies (O. xiangchengensis xiangchengensis vs. O. xiangchengensis deqinicus). A series of chromosomal variations may have facilitated the rapid evolution of amphibians in the QTP, and our study will provide support for further research on amphibian genetic diversity and biodiversity conservation.

Kimura's Theory of Non-Adaptive Radiation and Peto's Paradox: A Missing Link?

Karyotype diversity reflects genome integrity and stability. A strong correlation between karyotype diversity and species richness, meaning the number of species in a phylogenetic clade, was first reported in mammals over forty years ago: in mammalian phylogenetic clades, the standard deviation of karyotype diversity (KD) closely corresponded to species richness (SR) at the order level. These initial studies, however, did not control for phylogenetic signal, raising the possibility that the correlation was due to phylogenetic relatedness among species in a clade. Accordingly, karyotype diversity trivially reflects species richness simply as a passive consequence of adaptive radiation. A more recent study in mammals controlled for phylogenetic signals and established the correlation as phylogenetically independent, suggesting that species richness cannot, in itself, explain the observed corresponding karyotype diversity. The correlation is, therefore, remarkable because the molecular mechanisms contributing to karyotype diversity are evolutionarily independent of the ecological mechanisms contributing to species richness. Recently, it was shown in salamanders that the two processes generating genome size diversity and species richness were indeed independent and operate in parallel, suggesting a potential non-adaptive, non-causal but biologically meaningful relationship. KD depends on mutational input generating genetic diversity and reflects genome stability, whereas species richness depends on ecological factors and reflects natural selection acting on phenotypic diversity. As mutation and selection operate independently and involve separate and unrelated evolutionary mechanisms-there is no reason a priori to expect such a strong, let alone any, correlation between KD and SR. That such a correlation exists is more consistent with Kimura's theory of non-adaptive radiation than with ecologically based adaptive theories of macro-evolution, which are not excluded in Kimura's non-adaptive theory. The following reviews recent evidence in support of Kimura's proposal, and other findings that contribute to a wider understanding of the molecular mechanisms underlying the process of non-adaptive radiation.

Exploiting a living biobank to delineate mechanisms underlying disease-specific chromosome instability.

Chromosome instability (CIN) is a cancer hallmark that drives tumour heterogeneity, phenotypic adaptation, drug resistance and poor prognosis. High-grade serous ovarian cancer (HGSOC), one of the most chromosomally unstable tumour types, has a 5-year survival rate of only ~30% - largely due to late diagnosis and rapid development of drug resistance, e.g., via CIN-driven ABCB1 translocations. However, CIN is also a cell cycle vulnerability that can be exploited to specifically target tumour cells, illustrated by the success of PARP inhibitors to target homologous recombination deficiency (HRD). However, a lack of appropriate models with ongoing CIN has been a barrier to fully exploiting disease-specific CIN mechanisms. This barrier is now being overcome with the development of patient-derived cell cultures and organoids. In this review, we describe our progress building a Living Biobank of over 120 patient-derived ovarian cancer models (OCMs), predominantly from HGSOC. OCMs are highly purified tumour fractions with extensive proliferative potential that can be analysed at early passage. OCMs have diverse karyotypes, display intra- and inter-patient heterogeneity and mitotic abnormality rates far higher than established cell lines. OCMs encompass a broad-spectrum of HGSOC hallmarks, including a range of p53 alterations and BRCA1/2 mutations, and display drug resistance mechanisms seen in the clinic, e.g., ABCB1 translocations and BRCA2 reversion. OCMs are amenable to functional analysis, drug-sensitivity profiling, and multi-omics, including single-cell next-generation sequencing, and thus represent a platform for delineating HGSOC-specific CIN mechanisms. In turn, our vision is that this understanding will inform the design of new therapeutic strategies.

Evaluation of karyotype diversity in Indian traditional aromatic rice cultivars through EMA-based non-fluorescent Giemsa and fluorescent DAPI staining

Evaluation of karyotype diversity in Indian traditional aromatic rice cultivars through EMA-based non-fluorescent Giemsa and fluorescent DAPI staining

Characterization of Razi Bovine Kidney (RBK) Cell Line as a Sensitive Cell to Bovine Herpesvirus-1 (BoHV-1)

Viruses are obligate parasites and are completely dependent on host cells for survival and replication. RBK cell line developed and introduced by Razi Vaccine and Serum Research Institute, has been successfully established as a continuous cell line over successive passages.Viruses are obligate parasites that completely rely on host cells for survival and replication. Razi Bovine Kidney (RBK) cell line was introduced and developed by the Razi Vaccine and Serum Research Institute. It has been successfully established as a continuous cell line over successive passages. As demonstrated in this experimental study, the RBK cells have shown suitable sensitivity to certain viruses, including Bovine Herpesvirus-1 (BoHV-1) virus. In the present research, the RBK cell line characteristics were analyzed using molecular and karyotype methods and growth specifications. Cloning of the RBK cell line was performed using the limited dilution method, and each cell clone was quantitatively and qualitatively characterized. Four cell clones were compared based on their sensitivity to the BoHV-1 virus. Then, the RBK-D5 clone was selected as the most appropriate cell line for further studies. The RBK-D5 was subjected to tests for identity, chromosomal analysis, and doubling time. In the end, the origin of this cell line was confirmed by the PCR method. It was observed that the cell line exhibited karyotype diversity due to aneuploidy, which can be responsible for the procreation of chromosomal instability. This diversity represents chromosomal changes in the continuous cell line that carries the characteristic of an immortalized cell line. The RBK-D5 was found to be more sensitive to the BOHV-1 virus. Surprisingly, its titer was evaluated at 108.5 CCID50/ml. The obtained results suggested that the RBK cell line is suitable for the BoHV-1 virus and can be useful for virus detection, propagation, and quality control or viral titration.

Cross-species chromosome painting and repetitive DNA mapping illuminate the karyotype evolution in true crocodiles (Crocodylidae).

Crocodilians have maintained very similar karyotype structures and diploid chromosome numbers for around 100 million years, with only minor variations in collinearity. Why this karyotype structure has largely stayed unaltered for so long is unclear. In this study, we analyzed the karyotypes of six species belonging to the genera Crocodylus and Osteolaemus (Crocodylidae, true crocodiles), among which the Congolian endemic O. osborni was included and investigated. We utilized various techniques (differential staining, fluorescence in situ hybridization with repetitive DNA and rDNA probes, whole chromosome painting, and comparative genomic hybridization) to better understand how crocodile chromosomes evolved. We studied representatives of three of the four main diploid chromosome numbers found in crocodiles (2n = 30/32/38). Our data provided new information about the species studied, including the identification of four major chromosomal rearrangements that occurred during the karyotype diversification process in crocodiles. These changes led to the current diploid chromosome numbers of 2n = 30 (fusion) and 2n = 38 (fissions), derived from the ancestral state of 2n = 32. The conserved cytogenetic tendency in crocodilians, where extant species keep near-ancestral state, contrasts with the more dynamic karyotype evolution seen in other major reptile groups.

Microchromosome fusions underpin convergent evolution of chameleon karyotypes.

Evolutionary shifts in chromosome compositions (karyotypes) are major drivers of lineage and genomic diversification. Fusion of ancestral chromosomes is one hypothesized mechanism for the evolutionary reduction of the total chromosome number, a frequently implied karyotypic shift. Empirical tests of this hypothesis require model systems with variable karyotypes, known chromosome features, and a robust phylogeny. Here we used chameleons, diverse lizards with exceptionally variable karyotypes ($2n=20\text{-}62$), to test whether chromosomal fusions explain the repeated evolution of karyotypes with fewer chromosomes than ancestral karyotypes. Using a multidisciplinary approach including cytogenetic analyses and phylogenetic comparative methods, we found that a model of constant loss through time best explained chromosome evolution across the chameleon phylogeny. Next, we tested whether fusions of microchromosomes into macrochromosomes explained these evolutionary losses using generalized linear models. Multiple comparisons supported microchromosome fusions as the predominant agent of evolutionary loss. We further compared our results to various natural history traits and found no correlations. As such, we infer that the tendency of microchromosomes to fuse was a quality of the ancestral chameleon genome and that the genomic predisposition of ancestors is a more substantive predictor of chromosome change than the ecological, physiological, and biogeographical factors involved in their diversification.

Karyotype diversity in four Terminalia L. species and its taxonomic implications

AbstractFour Terminalia L. species namely, T. arjuna (Roxb.) Wight and Arn., T. bellirica (Gaertn.) Roxb., T. chebula Retz. and T. catappa L. were studied to evaluate the chromosomal relationship corresponding with their taxonomic characters. Analysis of mitotic metaphases showed that the somatic chromosome numbers and the centromeric formulas of these species were 2n = 24 (16m + 8sm) for T. arjuna, 2n = 48 (36m + 12sm) for T. bellirica, 2n = 48 (46m + 2sm) for T. chebula and 2n = 24 (24m) for T. catappa. Two pairs of satellites were found in T. bellirica and T. catappa. Based on different karyological data, T. chebula was positioned in 1A, T. arjuna and T. catappa in 1B and T. bellirica in 2B. Based on comparative karyomorphological data, T. bellirica and T. arjuna presented more advanced features in comparison with T. chebula and T. catappa, which also correlated with the taxonomic characters in respect of the evolutionary point of view. Therefore, the present investigation effectively evaluated chromosomal relationships with morphological implications that conferred upon evolutionary changes among these four Terminalia species.

CYTOGENETIC VARIABILITY OF THE HUTSUL BREED OF HORSES

Goal. Study of features of karyotypic variability of Hutsul horses. Methods. Cytogenetic analysis, micronucleus test. Results. The average rate of genomic disorders (aneuploidy) was 10.8%, with a range of values of this variability of 8.8%–11.1% in animals of the LLC "Krai Neba" and the National Nature Park "Hutsulshchyna" with a statistically insignificant difference between the mean values. The multiple increase in the number of chromosomes, polyploidy, was in the range of 1.1%–2.0%, which does not exceed the species of this variability. The magnitude of the asynchronous divergence of the centromeric regions of the chromosomes was 2.0%–6.0%, which corresponds to the spontaneous level for horses as a whole (2.2%–9.1%). Structural chromosome abnormalities (chromosomal breaks) in the horses of the Krai Neba LLC farm were not detected, and in the animals of the Hutsulshchyna National Nature Park they were 1.1%. The range of variability of lymphocytes with a micronucleus for animals of two farms was 4.0–4.2‰. The number of dinuclear lymphocytes (6.2‰) exceeded the mitotic index (4.3‰) with an insignificant difference in the average values, which indicates the absence of radionuclide contamination of the territory. Conclusions. The average number of aneuploid cells – 10.8%, polyploid – 1.4%, asynchronous divergence of the centromeric regions of chromosomes – 3.9% and the proportion of chromosomal breaks – 1.1%. The proportion of lymphocytes with a micronucleus – 4.0–4.2–4, dinuclear lymphocytes – 6.2‰ and the mitotic index – 4.3‰, which indicates the stability of the karyotype of the studied horses.

Genome Shock in a Synthetic Allotetraploid Wheat Invokes Subgenome-Partitioned Gene Regulation, Meiotic Instability and Karyotype Variation.

It becomes increasingly evident that interspecific hybridization at homoploid level or coupled with whole genome duplication (i.e., allopolyploidization) has played a major role in biological evolution. Yet, the direct impact of hybridization and allopolyploidization on genome structure and function, phenotype, and fitness remains to be fully understood. Synthetic hybrids and allopolyploids are trackable experimental systems to address this issue. Here, we resynthesized a pair of reciprocal F1 hybrids and corresponding reciprocal allotetraploids using the two diploid progenitor species, Triticum urartu (AA) and Aegilops tauschii (DD), of bread wheat (Triticum aestivum L., BBAADD). By comparing phenotypes related to growth, development and fitness, andanalyzing genome expression in both hybrids and allotetraploids in relation to parents, we find the types and trends of karyotype variation in the immediately formed allotetraploids, are correlated with both meiosis instability and chromosome- and subgenome-biased expression. We document clear advantages of allotetraploids over diploid F1 hybrids in several morphological traits including fitness, which mirror the tissue- and developmental stage-dependent subgenome-partitioning of the allotetraploids. The allotetraploids are meiotically unstable primarily due to homoeologous pairing that varies dramatically among the chromosomes. Nonetheless, the manifestation of organismal karyotype variation and occurrence of meiotic irregularity are not concordant, suggesting a role of functional constraints probably imposed by subgenome- and chromosome-biased gene expression. Our results provide new insights into the direct impacts and consequences of hybridization and allopolyploidization, which are relevant to evolution and likely informative to crop improvement by synthetic polyploid approaches.

P-703 The role of maternal polymorphic karyotype variants among embryonic ploidy and mosaicism status in patients undergoing IVF treatments

Abstract Study question Is there a relationship between the chromosomal status of biopsied embryos and the presence of polymorphic variants in the female karyotype in IVF cycles? Summary answer The chromosomal status of biopsied embryos is prejudiced because of the presence of specific maternal polymorphic variants (qh-, qh+ and ps+) or combinations of them. What is known already Due to the increasing average age of patients who undergo IVF cycles with their own oocytes, more cycles are performed with embryo biopsy for preimplantation genetic test of aneuploidies (PGT-A). Thus, advanced maternal age has been defined as the main factor causing embryonic chromosomal abnormalities. However, few studies have established direct relationships with other factors. The prevalence of chromosomal polymorphic variants has a higher incidence in the infertile population, which is why there is a need to know the role they play in the genetic inheritance of embryos. Study design, size, duration Retrospective evaluation of a cohort of women who underwent autologous IVF cycles and karyotyping. The sample included 162 IVF cycles with embryo biopsy on D5 and/or D6 for PGT-A, performed between July 2017-December 2021: control group (CG) with normal karyotype (86) and study group (SG) with presence of polymorphisms (76). We studied the connection between maternal karyotype polymorphisms and molecular genetic outcomes in terms of euploid, mosaic, and aneuploid blastocyst rates. Participants/materials, setting, methods The analysis of the karyotype of women, prior to the IVF cycle, was performed using the guidelines of the International System for Human Cytogenetic Nomenclature (ISCN). The trophoectoderm biopsies on D5 and/or D6 blastocysts were analysed by NGS using the Illumina platform (VeriSeq Illumina®, San Diego, CA, USA). The association between the different polymorphic variants in the female karyotype and chromosomal status of embryos was analysed using R (v. 4.2.0) statistical software. Main results and the role of chance We analyzed the results of 483 embryos from 162 IVF-PGT-A cycles. Mean female age was 39.05±2.72 (CG) and 38.97±2.90 (SG). Mean number of mature oocytes (MII) was 7.16±3.94 (CG) and 8.01±5.33 (SG). Mean number of biopsied embryos was 2.97±2.15 (CG) and 2.93±1.88 (SG). No statistically significant differences were found between the CG and SG groups in terms of the rate of euploid embryos: 26.99% vs 21.50% (p = 0.3), transferable mosaic embryos: 8.90% vs 6.76% (p = 0.5), aneuploid embryos: 61.98% vs 69.96% (p = 0.12) and non-informative embryos: 2.13% vs 1.78% (p = 0.2), respectively. However, an increase in the rate of chromosomally abnormal embryos was observed when analysing each polymorphism individually. In females carrying the qh+ variant, we found a statistically significant decrease in the euploid embryo rate: 10.97% vs 26.00% found in CG (p = 0.036). Moreover, the variants qh+ and ps+ increased the rate of aneuploid embryos: 84.17% vs 63.48% in CG (p = 0.013) and 73.52% vs 61.30% in CG (p = 0.021), respectively. Furthermore, it is found that the qh- variant increased the rate of transferable mosaic embryos: 20.00% vs 8.90% in CG (p = 0.025). The results were corrected for confounding variables such as maternal age, oocyte origin and male factor variables, including polymorphic variants in the male karyotype. Limitations, reasons for caution Presence of unmeasured variables that may influence the results. Larger prospective studies including homogeneous cohorts are needed in order to corroborate our initial results. Wider implications of the findings The results show that polymorphic variants in the female karyotype may have a direct effect on the embryonic ploidy and mosaicism status. Therefore, it would be advisable for patients who undergo IVF-PGT-A cycles to have a karyotype performed and be informed of the implications that it may entail. Trial registration number Not applicable

Characterization of repetitive DNA on the genome of the marsh rat Holochilus nanus (Cricetidae: Sigmodontinae).

Repetitive DNA are sequences repeated hundreds or thousands of times and an abundant part of eukaryotic genomes. SatDNA represents the majority of the repetitive sequences, followed by transposable elements. The species Holochilus nanus (HNA) belongs to the rodent tribe Oryzomyini, the most taxonomically diverse of Sigmodontinae subfamily. Cytogenetic studies on Oryzomyini reflect such diversity by revealing an exceptional range of karyotype variability. However, little is known about the repetitive DNA content and its involvement in chromosomal diversification of these species. In the search for a more detailed understanding about the composition of repetitive DNA on the genome of HNA and other species of Oryzomyini, we employed a combination of bioinformatic, cytogenetic and molecular techniques to characterize the repetitive DNA content of these species. RepeatExplorer analysis showed that almost half of repetitive content of HNA genome are composed by Long Terminal Repeats and a less significant portion are composed by Short Interspersed Nuclear Elements and Long Interspersed Nuclear Elements. RepeatMasker showed that more than 30% of HNA genome are composed by repetitive sequences, with two main waves of repetitive element insertion. It was also possible to identify a satellite DNA sequence present in the centromeric region of Oryzomyini species, and a repetitive sequence enriched on the long arm of HNA X chromosome. Also, comparative analysis between HNA genome with and without B chromosome did not evidence any repeat element enriched on the supernumerary, suggesting that B chromosome of HNA is composed by a fraction of repeats from all the genome.

Cytogenetic evidence of hybridization in Prosopis alba, P. hassleri, and P. fiebrigii in the semiarid-humid Chaco transition

Hybridization is a common and widespread phenomenon in vascular plants, leading to genetic exchange between related species. Interspecific hybridization has been extensively reported in Prosopis, a key genus of the Gran Chaco Americano, when species grow in sympatry or have adjacent distributions. Here, we performed a cytogenetic study in a hybrid zone of Prosopis alba, P. hassleri, and P. fiebrigii in southern South America. We characterized the karyotypes of pure species and the putative interspecific hybrids using chromosome fluorescent banding. Two karyotypes according to the heterochromatin pattern were identified, one corresponding to P. alba and the other to P. hassleri and P. fiebrigii; hybrid individuals presented P. alba or P. hassleri/P. fiebrigii karyotypes. The karyotypic formula and the number of nucleolar organizer regions were the same for all the studied morphotypes. Chromosome similarity among different species of the genus allows a continued hybridization and introgression between species and lends support to the hypothesis of a relatively recent diversification of Prosopis. Studying karyotype variation within a population could be a novel approach to the cytogenetic study of hybrids in the future.

Meiotic pairing irregularity and homoeologous chromosome compensation cause rapid karyotype variation in synthetic allotetraploid wheat.

Allopolyploidization may initiate rapid evolution due to heritable karyotypic changes. The types and extents of these changes, the underlying causes, and their effects on phenotype remain to be fully understood. Here, we designed experimental populations suitable to address these issues using a synthetic allotetraploid wheat. We show that extensive variation in both chromosome number (NCV) and structure (SCV) accumulated in a selfed population of a synthetic allotetraploid wheat (genome Sb Sb DD). The combination of NCVs and SCVs generated massive organismal karyotypic heterogeneity. NCVs and SCVs were intrinsically correlated and highly variable across the seven sets of homoeologous chromosomes. Both NCVs and SCVs stemmed from meiotic pairing irregularity (presumably homoeologous pairing) but were also constrained by homoeologous chromosome compensation. We further show that homoeologous meiotic pairing was positively correlated with sequence synteny at the subtelomeric regions of both chromosome arms, but not with genic nucleotide similarity per se. Both NCVs and SCVs impacted phenotypic traits but only NCVs caused significant reduction in reproductive fitness. Our results implicate factors influencing meiotic homoeologous chromosome pairing and reveal the type and extent of karyotypic variation and its immediate phenotypic manifestation in synthetic allotetraploid wheat. This has relevance for our understanding of allopolyploid evolution.

Multiple Chromosomal Polymorphism in Birch Mice of the Subtilis Group (Rodentia, Dipodoidea, <i>Sicista</i>) from Saratov Right Bank

Cytogenetic analysis (routine, G-, C-, AgNOR-chromosome banding) allowed to obtain new data on chromosomal polymorphism in the population (n = 13) of Sicista sp. 1, representative of the Sicista subtilis group from the Saratov Region, right bank of Volga River. It was shown that in the studied polymorphic population of a species from the northern part of the species' range (Voskresensky district of the Saratov region) the diploid number of chromosomes varies from 2n = 22 to 2n = 24, and the number of autosome arms from NFa = 39 to NFa = 44, and the sample includes the following 6 karyotype variants: with 2n = 24, NFa = 44; 2n = 24, NFa = 43; 2n = 23, NFa = 40; 2n = 23, NFa = 41; 2n = 22, NFa = 39; 2n = 22, NFa = 40. Based on G‑banding method, the determined intrapopulation chromosomal polymorphism in Sicista sp. 1 was defined by two chromosomal rearrangements: tandem translocation involving two biarmed autosomes No 4 and 10 and a pericentric inversion of pair No 6. In the studied sample (n = 13), a stable advantage of heterozygotes was revealed for both structural chromosomal mutations and the chromosomal polymorphism is characterized as balanced or heterozygous. The potential role of the identified polymorphism in chromosomal evolution and adaptive strategy of the species is discussed.

Chromosome Asynapsis Is the Main Cause of Male Sterility in the Interspecies Hybrids of East Asian Voles (Alexandromys, Rodentia, Arvicolinae).

Closely related mammalian species often have differences in chromosome number and morphology, but there is still a debate about how these differences relate to reproductive isolation. To study the role of chromosome rearrangements in speciation, we used the gray voles in the Alexandromys genus as a model. These voles have a high level of chromosome polymorphism and substantial karyotypic divergence. We investigated testis histology and meiotic chromosome behavior in the captive-bred colonies of Alexandromys maximowiczii, Alexandromys mujanensis, two chromosome races of Alexandromys evoronensis, and their interracial and interspecies hybrids, to explore the relationship between karyotypic differences and male hybrid sterility. We found that the seminiferous tubules of the males of the parental species and the interracial hybrids, which were simple heterozygotes for one or more chromosome rearrangements, contained germ cells at all stages of spermatogenesis, indicating their potential fertility. Their meiotic cells displayed orderly chromosome synapsis and recombination. In contrast, all interspecies male hybrids, which were complex heterozygotes for a series of chromosome rearrangements, showed signs of complete sterility. Their spermatogenesis was mainly arrested at the zygotene- or pachytene-like stages due to the formation of complex multivalent chains, which caused extended chromosome asynapsis. The asynapsis led to the silencing of unsynapsed chromatin. We suggest that chromosome asynapsis is the main cause of meiotic arrest and male sterility in the interspecies hybrids of East Asian voles.