Continuous occurrence of intra-individual chromosome rearrangements in the peach potato aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae)

Analysis of the holocentric mitotic chromosomes of the peach-potato aphid, Myzus persicae (Sulzer), from clones labelled 50, 51 and 70 revealed different chromosome numbers, ranging from 12 to 14, even within each embryo, in contrast to the standard karyotype of this species (2n?=?12). Chromosome length measurements, combined with fluorescent in situ hybridization experiments, showed that the observed chromosomal mosaicisms are due to recurrent fragmentations of chromosomes X, 1 and 3. Contrary to what has generally been reported in the literature, X chromosomes were frequently involved in recurrent fragmentations, in particular at their telomeric ends opposite to the nucleolar organizer region. Supernumerary B chromosomes have been also observed in clones 50 and 51. The three aphid clones showed recurrent fissions of the same chromosomes in the same regions, thereby suggesting that the M. persicae genome has fragile sites that are at the basis of the observed changes in chromosome number. Experiments to induce males also revealed that M. persicae clones 50, 51 and 70 are obligately parthenogenetic, arguing that the reproduction by apomictic parthenogenesis favoured the stabilization and inheritance of the observed chromosomal fragments.     

Fast chromosomal evolution and karyotype instability: recurrent chromosomal rearrangements in the peach potato aphid Myzus persicae (Hemiptera: Aphididae)

The occurrence of karyotype variations with respect to both chromosome number and structure has been frequently reported in aphids. Here, we review recent data attesting to the presence of recurrent chromosomal changes in the karyotype of the peach potato aphid Myzus persicae, where clones presenting metaphases with different chromosome number (from 12 to 17) have been observed, also comparing plates obtained within the same embryo. According to the available data, M. persicae autosomes 3 and 1 are the chromosomes mostly involved in changes compared to other autosomes, suggesting that they could have sites more susceptible to fragmentation. Chromosomal fissions involving the X chromosomes have also been observed, suggesting that they may have fragile sites located at the termini opposite to the nucleolar organizer regions‐bearing telomere. The presence of holocentric chromosomes and reproduction by apomictic parthenogenesis, together with a constitutive expression of telomerase, could explain the inheritance of the observed chromosomal instability in aphids. Considering that chromosomal changes may affect the host choice and could also favour speciation, it would be intriguing to confirm whether the observed karyotype variants have effects over short temporal and spatial scales.     

Evolution of karyotype,sex chromosomes,and meiosis in mygalomorph spiders (Araneae: Mygalomorphae)

Spider diversity is partitioned into three primary clades, namely Mesothelae, Mygalomorphae, and Araneomorphae. Mygalomorph cytogenetics is largely unknown. Our study revealed a remarkable karyotype diversity of mygalomorphs. Unlike araneomorphs, they show no general trend towards a decrease of 2n, as the chromosome number was reduced in some lineages and increased in others. A biarmed karyotype is a symplesiomorphy of mygalomorphs and araneomorphs. Male meiosis of some mygalomorphs is achiasmatic, or includes the diffuse stage. The sex chromosome system X₁X₂0, which is supposedly ancestral in spiders, is uncommon in mygalomorphs. Many mygalomorphs exhibit more than two (and up to 13) X chromosomes in males. The evolution of X chromosomes proceeded via the duplication of chromosomes, fissions, X–X, and X‐autosome fusions. Spiders also exhibit a homomorphic sex chromosome pair. In the germline of mygalomorph males these chromosomes are often deactivated; their deactivation and pairing is initiated already at spermatogonia. Remarkably, pairing of sex chromosomes in mygalomorph females is also initiated at gonial cells. Some mygalomorphs have two sex chromosome pairs. The second pair presumably arose in early‐diverging mygalomorphs, probably via genome duplication. The unique behaviour of spider sex chromosomes in the germline may promote meiotic pairing of homologous sex chromosomes and structural differentiation of their duplicates, as well as the establishment of polyploid genomes. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 377–408.     

Stable versus unstable orientations of sex chromosomes in two grasshopper species

The structural basis of orientation stability was investigated. The stable unipolar orientation of the Melanoplus sanguinipes X-chromosome univalent is unique in that it is stable without tension created by forces towards opposite poles; tension is thought to be the principle component in stabilizing kinetochore orientations to a pole. Stable orientation of the X chromosome in Melanoplus sanguinipes was compared with unstable X orientation in Melanoplus differentialis. Ten cells (five of each species) were studied, firstly in living cultures where chromosome behavior was followed, then by serial-section electron microscopy where the structural basis for chromosome behavior was examined. Microtubules other than kinetochore microtubules were observed impinging on the X chromosomes. One end of these microtubules was buried in chromatin, while the other ran towards a pole. The X chromosomes of M. sanguinipes had more of these microtubules than did M. differentialis X chromosomes. It is suggested that M. sanguinipes X chromosomes are less condensed than M. differentialis X chromosomes and so allow more microtubules to penetrate the chromosome. The extra microtubules impinging on the M. sanguinipes X chromosome probably prevent reorientation by inhibiting the turning of the chromosome towards the opposite pole, i.e., more force is needed to turn a kinetochore towards the opposite pole than can be generated and attempts at reorientation fail. This may be analogous to the effect that tension has on the orientation stability of bivalents.     

Accumulation of chloroplast DNA sequences on the Y chromosome of Silene latifolia

Silene latifolia is a model dioecious plant with heteromorphic sex chromosomes. The Y chromosome is the largest in this species. Theoretical models propose an accumulation of repetitive DNA sequences in non-recombining parts of the Y chromosome. In this study, we isolated a BAC7H5 clone preferentially hybridizing to the Y chromosome of S. latifolia. Sequence analysis revealed that this BAC7H5 contains part of the chloroplast genome, indicating that these chloroplast sequences have accumulated on the Y chromosome and also may contribute to its large size. We constructed Y chromosome- and X chromosome-specific libraries and screened them to find Y- and/or X-linked copies of chloroplast sequences. Sequence analysis revealed higher divergence of a non-genic region of the chloroplast sequences located on the Y chromosome while genic regions tested showed only very low (max 0.9%) divergence from their chloroplast homologues.     

A naturally occurring chromosomal translocation in Myzus persicae (Sulzer)

Populations of M.persicae from glasshouses in Britain were found to have a structurally heterozygous chromosome complement. Biometric data from somatic metaphase chromosomes, and the pairing configurations of chromosomes at spermatocyte meiosis, indicate either a simple or a reciprocal translocation involving autosomes 1 and 3. All except one of the clones started from these populations showed high levels of esterase activity indicative of resistance to organophosphorus insecticides. The British translocated clones were all androcyclic in reproductive character, but of several distinct genotypes. A similar or identical translocation was found in seven out of nine clones started from M.persicae collected in the field in Japan. The translocation was present in Japanese M.persicae of all reproductive categories, being somehow maintained in the sexual breeding system of the aphid. In breeding experiments, translocation heterozygosity was inherited independently from colour and reproductive characters. The translocation was also found in a sample of M.persicae from southern California.     

Cytomolecular analysis of the male sex chromosome of Tropidacris cristata grandis (Thunberg, 1824) (Orthoptera: Romaleidae)

Many species of grasshopper have an XX/XO sex chromosome system, including Tropidacris cristata grandis (23, XX/XO). The X chromosome behaves differently from the autosomes, but little is known about its origin and molecular composition. To better understand the genomic composition and evolutionary processes involved in the origin of the sex chromosomes, we undertook an analysis of its meiotic behavior, heterochromatin distribution and microdissection in T. c. grandis. Analysis of meiotic cells revealed a difference in the behavior of the X chromosome compared to the autosomes, with different patterns of condensation and cellular arrangement. Heterochromatic terminal blocks were predominant. The chromosome painting revealed a bright block in the centromeric/pericentromeric region of the X chromosome and slight markings in the other regions. In the autosomes, the X chromosome probe hybridized in the centromeric/pericentromeric region, and hybridization signals on terminal regions corresponding to the heterochromatic regions were also observed. The results showed that the X chromosome contains a significant amount of repetitive DNA. Based on the hybridization pattern, it is possible that the autosomes and sex chromosomes of T. c. grandis have a similar composition of repetitive DNAs, which could mean that the X chromosome has an autosomal origin.     

Implications of phenotypic variation of Myzus persicae (Hemiptera: Aphididae) for biological control on greenhouse pepper plants

Variation in vulnerability to natural enemies, reproductive rate and insecticide resistance among phenotypes of Myzus persicae (Sulzer) has been shown to have the potential to disrupt biological control and IPM of this species, and movement of particularly troublesome phenotypes in international horticultural trade could be cause for concern. Three important components of fitness, vulnerability to parasitoids, reproduction and insecticide resistance were determined in three clones of M. persicae originating from prevalent phenotype populations on pepper crops in greenhouses in British Columbia, Canada. One of these phenotypes appeared to be consistently involved in outbreaks in commercial operations. These clones were also characterized for their DNA microsatellite genotype and compared with genotypes of M. persicae from Europe. The clone involved in outbreaks in commercial greenhouses showed reduced vulnerability to parasitoids, and a higher reproductive rate compared to the other two clones suggesting that these traits may have been involved in outbreaks. As in M. persicae European clones, a higher reproductive rate was correlated with a lack of esterase‐based resistance (primarily to organophosphates and, to some extent, to carbamates and pyrethroids). However, microsatellite analysis demonstrated that the three clones investigated in British Columbia had unique genotypes, and therefore there was no evidence for their movement in international trade.     

DNase I sensitivity of Microtus agrestis active,inactive and reactivated X chromosomes in mouse-Microtus cell hybrids

We isolated Microtus agrestis-mouse somatic cell hybrid clones which had retained either the active or the inactive M. agrestis X chromosome. In both hybrid clones the X chromosomes retained their original chromatin conformation as studied by the in situ nick translation technique — the active X chromosome retained its high sensitivity to DNase I while the inactive one remained insensitive. A clone in which the hypoxanthine guanine phosphoribosyltransferase (HPRT) gene had been spontaneously reactivated was isolated from the hybrid containing the inactive X chromosome. The in situ nick translation technique was used to study possible DNA conformation changes in the euchromatin of the inactive X chromosome with special reference to the reactivated HPRT locus. We found that the euchromatin in this X chromosome exhibited the same low sensitivity to DNase I as is characteristic of the inactive X chromosome.Professor Marcus passed away on 2 January 1987     

Behavioural response of green peach aphid Myzus persicae (Sulzer) to volatiles from different rosemary (Rosmarinus officinalis L.) clones

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DNA CONTENT OF SEVEN SPECIES OF ASTEREAE AND ITS SIGNIFICANCE TO THEORIES OF CHROMOSOME EVOLUTION IN THE TRIBE

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彭泽鲫两个雌核发育克隆的染色体组型分析

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Generation of Five High-Complexity Painting Probe Libraries from Flow-Sorted Mouse Chromosomes

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Localization of BAC clones on mitotic chromosomes of <Emphasis Type="Italic">Musa acuminata</Emphasis> using fluorescence <Emphasis Type="Italic">in situ</Emphasis> hybridization

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Chromosomes in somatic hybrids between Nicotiana plumbaginifolia and a monoploid potato

Summary Leaf mesophyll protoplasts of the monohaploid potato (Solanum tuberosum L.) clone H7322 were fused with callus protoplasts of nitrate reductase deficient (NR^–) mutants Cnx 20 and NA 36 of Nicotiana plumbaginifolia. Somatic hybrid lines were selected for nitrate reductase proficiency. All callus lines tested appeared to be stable for the retention of the potato chromosome carrying the compensating NR gene when grown for over 1.5 years in the absence of nitrate. Shoots were regenerated from six different fusion lines of Cnx 20 + H7322 24 months after fusion. Chromosomal analysis in callus cultures revealed that in both fusion combinations 40–120 N. plumbaginifolia chromosomes were present, as were 9–20 potato chromosomes. Cells with 17 potato chromosomes in combination with a relatively small number (31) of N. plumbaginifolia chromosomes were found in one line. Preferential loss of species-specific chromosomes was not observed. Analysis of regenerating tissue from three lines of Cnx 20 + H7322 revealed that after 24 months of culture intra- and intergeneric translocations, fragments and deletions were present. Elimination of the potato and N. plumbaginifolia chromosomes had taken place before and after genome doubling.     

The JIL-1 kinase regulates the structure of Drosophila polytene chromosomes

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Chromosome numbers and DNA content in Bromeliaceae: additional data and critical review

For the large Neotropical plant family Bromeliaceae, we provide new data on chromosome numbers, cytological features and genome size estimations, and combine them with data available in the literature. Root‐tip chromosome counts for 46 species representing four subfamilies and a literature review of previously published data were carried out. Propidium iodide staining and flow cytometry were used to estimate absolute genome sizes in five subfamilies of Bromeliaceae, sampling 28 species. Most species were diploid with 2n = 50 in Bromelioideae, Puyoideae and Pitcairnioideae, followed by 2n = 48 observed mainly in Tillandsioideae. Individual chromosome sizes varied more than tenfold, with the largest chromosomes observed in Tillandsioideae and the smallest in Bromelioideae. Genome sizes (2C‐values) varied from 0.85 to 2.23 pg, with the largest genomes in Tillandsioideae. Genome evolution in Bromeliaceae relies on two main mechanisms: polyploidy and dysploidy. With the exception of Tillandsioideae, polyploidy is positively correlated with genome size. Dysploidy is suggested as the mechanism responsible for the generation of the derived chromosome numbers, such as 2n = 32/34 or 2n = 48. The occurrence of B chromosomes in the dysploid genus Cryptanthus suggests ongoing speciation processes closely associated with chromosome rearrangements. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 349–368.     

Cytogeographical study of four aneuploids ofCarex oxyandra Kudo in Japan

Chromosome numbers were determined for 342 clones ofCarex oxyandra collected from 35 localities in Hokkaido, Honshu, Shikoku and Kyushu, Japan. Four intraspecific aneuploids, 2n=18, 20, 24 and 26, were found. In meiotic division, only bivalent chromosomes were observed in all clones at metaphases I and II, suggesting that the aneuploids are established gamodemes. In the mitotic metaphase chromosomes, trimodal variation in chromosome length was observed. The 2n=26 clones found on Mt. Hiko had two particularly small chromosomes. The cytodemes with higher number of chromosomes are distributed in more southern areas of Japan.Carex oxyandra, therefore, accompanied with chromosome fragmentations, might spread the geographical distribution to the southern parts. The morphological characters of leaves, spikes, scales, perigynia and nuts were similar among the four cytodemes, except for the small leaves on plants from Yaku Island.