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1.
The endemic grasshopper Cryptobothrus chrysophorus is widely distributed throughout S.E. Australia and its populations display an extensive and spectacular pattern of autosomal variation. While the standard telocentric complement of three long (L1–3), six medium (M4–9) and two short (S10–11) autosome pairs is present throughout most of its range, two quite distinct chromosome races can be defined within this species. Populations in the northern part of its distribution (northern N.S.W. and southern Queensland-northern race) are differentiated from the remainder (southern race) by fixed blocks of distal heterochromatin on autosomes M4, 5, 6, 8 and 9 and by differences in the character of the megameric M7 chromosome. Additionally, while many populations in both races show a polymorphic system of supernumerary segments on the two smallest autosomes (S10–11), that found in the northern race is both more variable and more complex. On the other hand all the populations of the southern race we have examined are polymorphic for a series of centric shifts which convert telocentrics into acro- or meta-centrics. These occur more commonly in the megameric M7 and the two smallest autosomes (S10–11) although in one population (Forbes Creek, N.S.W.) at least 12 different shifts involving 8 of the autosomes (L3, M4, 5, 6, 7, 8, 9 and S10) are known. By contrast, in the northern erace only the small autosomes (S10–11) show centric shifts. These several floating and fixed variants thus involve all chromosomes of the standard set other than the two largest autosomes (L1–2) and the X-chromosome, which appear to be invariate. Finally, morphologically distinct supernumerary (B) chromosomes, intermediate in size between the standard S10 and the M9 elements, are found in both races but are especially common in Tasmania, the most southerly point of the species range. These B-chromosomes are partly heterochromatic and partly euchromatic so that they too add to the considerable heterochromatin variation in this species. 相似文献
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Synthetic F1 hybrids between individuals taken from selected populations of the northern (Glenn Innés, Bolivia Hill) and southern (Forbes Creek, Mount Aggie) chromosome races of the grasshopper Cryptobothrus chrysophorus confirm that these two races are indeed distinguished by fixed differences in heterochromatin content. These differences affect five of the six medium sized members of the complement (M 4, 5, 6, 8 and 9). Added to this there is a marked change in the character of the remaining medium pair (M 7) which functions as the megameric in this species. — Meiosis in F1 males is characterised by the presence of univalency in from 22–32% of the meiocytes. This appears to be genotypic in causation and may involve from one to three chromosome pairs in any one cell. Laggards produced from such univalents lead to a failure of anaphase separation at either first or second division or at both of them. Consequently from 17–36% of the sperm produced are giant (diploid or tetraploid) in size. Added to this the medium members commonly form end to end associations involving the heterochromatic (northern race) and euchromatic (southern race) terminii. This is a modified form of the heterochromatic end associations which occur between homologous medium pairs in northern populations. The two small pairs (S10 and 11) show comparable behaviour in both races when they carry terminal heterochromatic supernumerary segments. Such associations persist despite the fact that they are non-chiasmate in character. Moreover, despite the asynapsis found in F1 males they produce F2s when allowed to intersib mate, although many of the embryos fail to develop, presumably as a result of genotypic imbalance, or else are aneuploid in constitution. In the F2s that do survive to maturity the chromosome differences which distinguish the northern and southern forms are recombined to give a wide variety of karyotypes in which the observed pairing is much improved and from which F3s were subsequently obtained. 相似文献
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A probable role of heterochromatin variation in male meiosis has been evaluated using fertile and infertile Indian mole rat males (Nesokia) with polymorphic X and/or Y chromosomes. A comprehensive study of tubular histology, meiotic progression, and X-Y chromosome pairing was undertaken. Despite heterochromatin variation, spermatogenesis was found to be complete in all individuals. Patterns of X-Y synaptonemal complex pairing varied considerably from extensive synapsis in individuals with a normal heterochromatin complement, through end-to-end synapsis, to X and Y univalents in those with different degrees of loss of heterochromatin. Changes in the gonadal histology corresponding to heterochromatin variation were also observed. Loss of some coding DNA sequences in polymorphic X-chromosomes otherwise located at specific sites in the X-chromosome heterochromatin have been linked directly to modifications of the reproductive process. This is thought to be mediated by an altered X-chromosome activity during spermatogenesis or regulation of other locus/loci involved in fertility or reproduction. 相似文献
4.
Ten individuals of Uromys caudimaculatus sampled from Queensland gave evidence for the occurrence of two distinct chromosome races characterised by marked differences in their pattern of C-banding. In all four individuals from the north, thirteen of the twenty three chromosome which make up the standard haploid set had substantial distal C-blocks in addition to the smaller centric blocks which characterise all chromosomes other than the Y. Additionally two pairs had an interstitial block. By contrast none of the six southern individuals had fixed distal blocks though all of them except the Y carry pro-centric C-blocks and again one pair showed an interstitial block. The southern karyotype was, however, characterised by the presence of from six to nine mitotically stable supernumerary chromosomes all of which were totally C-positive despite the fact that at least five morphologically distinguishable types have been defined. While the relationship of these two types of constitutive heterochromatin remains to be clarified the large amount present in both northern and southern animals suggests that heterochromatin plays an important role in the basic biology of this species. 相似文献
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Canio G. Vosa 《Chromosoma》1973,43(3):269-278
The heteroohromatin of Scilla sibirica, consists of two distinct types: 1) showing enhanced Quinacrine fluorescence and located near the centromere of all the chromosomes of the complement, and 2) with reduced Quinacrine fluorescence and located in various positions along the chromosomes. After a denaturation-reannealing treatment both heterochromatin types are stained by Giemsa, and by acetic-orcein. Acetic-orcein, however, tends to stain preferentially the reduced fluorescence segments. An analysis of chromosome variation in a population of twenty plants, reveals that all the plants are unique in their heterochromatic segment endowment. All the chromosomes are polymorphic but there is a certain constancy for band patterns in individual chromosome types, and for the number of bands per chromosome complement. 相似文献
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S R Rao K Vasantha B K Thelma R C Juyal S C Jhanwar 《Cytogenetics and cell genetics》1983,35(4):233-237
Nesokia indica, the Indian mole rat, exhibits extensive variability (polymorphism) for the constitutive heterochromatin of the X and Y chromosomes. These polymorphic X and Y types range from a large metacentric chromosome to a small acrocentric one and occur in different frequencies in the population. On the assumption that there is random mating among individuals carrying these various X and Y chromosomes, the population shows Hardy-Weinberg proportions for the genotypes. However, notwithstanding the partial or total loss of constitutive heterochromatin of the X and Y chromosomes in a few individuals, its retention in most of the animals seems obligatory to the population at large. Hence, we suggest that the C-heterochromatin plays a "regulatory" role in the population dynamics of this species. 相似文献
7.
Heterochromatin 总被引:8,自引:0,他引:8
Hennig W 《Chromosoma》1999,108(1):1-9
The properties of heterochromatin are reconsidered in the context of our present understanding of gene silencing, telomeric
and centromeric properties, position-effect variegation and X-chromosome inactivation. It is proposed that the chromatin in
heterochromatic chromosomal regions is generally similar in its molecular composition to that in silenced chromosomal regions.
Heterochromatic appearance hence reflects not a particular quality of the respective chromosomal regions but only a specific
kind of chromatin packaging comparable to that required for the inactivation of genes. This packaging may be initiated by
particular signals in the DNA but can be propagated over more extended chromosomal regions by the formation of multiprotein
complexes that interact with histones and possibly cell-specific additional components (RNA or proteins) that determine the
status of the chromosome in a particular cell type.
Received: 15 November 1998 / Accepted: 8 December 1998 相似文献
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The chromosomes of several cultivatedTulipa species of subg.Leiostemones were examined in conventionally stained and C-banded preparations. The heterochromatin content varied from almost none to 45%. Several chromosome types were recognized with respect to chromosome morphology and heterochromatin distribution, and groups of species with common chromosome characteristics could be identified. These karyological relationships are discussed with respect to the groups formed on the basis of floral and bulb charateristics. 相似文献
10.
Heterochromatin and repetitive DNA frequency variation in regenerated plants of Helianthus annuus L.
L. Natali T. Giordani G. Cionini C. Pugliesi M. Fambrini A. Cavallini 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,91(3):395-400
Plant regeneration from cotyledons of seeds of a single progeny of a pure line of Helianthus annuus was studied in respect of the nuclear DNA contents of control and regenerated plants. Control plants were divided into two groups: those developed from seeds at the periphery of the inflorescence (showing a high basic 4C DNA content) and those from seeds developed in the middle of the inflorescence (showing a low basic 4C DNA content). It was observed that plants from peripheral seeds have a higher morphogenetic potential than those from central seeds. Cytophotometric analyses indicated that plants regenerated from cotyledons of both peripheral and central seeds show the same basic 4C DNA amount, which is higher that that observed in vivo in peripheral seeds. Molecular analysis by slot blotting and hybridization with different DNA families showed that the difference in nuclear DNA content between plants from peripheral and central seeds in vivo are mainly related to differences in the frequency of highly repeated, slow medium repeated (MR2), and ribosomal DNA families; by contrast, the increase in DNA amount in regenerated plants is mainly due to fast medium repeated sequences (MR1). Moreover, the frequency of kinetically isolated unique sequences was higher in peripheral seeds than in central ones and still higher in regenerated plants. Optical-density measurements of interphase nuclei showed an increase of heterochromatin in regenerated plants, suggesting that, whatever DNA is amplified in these plants, it remains condensed and probably inactive.Research supported by National Research Council of Italy, Special Project RAISA, Sub-project No. 2, Paper No. 2069 相似文献
11.
The chromosomes of several cultivatedTulipa species belonging to the subg.Eriostemones were examined using conventional staining and C-banding techniques. Most of the species have lightly banded chromosomes with heterochromatin content varying from nil to about 15%. The banding patterns of several taxa are described and discussed in regard to species relationships. 相似文献
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Heterochromatin revisited 总被引:10,自引:0,他引:10
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C. Barigozzi G. Badaracco P. Plevani L. Baratelli S. Profeta E. Ginelli R. Meneveri 《Chromosoma》1984,90(5):332-337
A bisexual species of the genus Artemia (Crustacea, Phyllopoda), Artemia franciscana Barigozzi of San Francisco Bay and a parthenogenetic population of Artemia sp. of Tsing-Tao (China), both with 42 chromosomes, were compared with respect to the microscopic structure of the interphase larval nucleus, the microscopical structure of the prophase chromosomes and the DNA structure. — Artemia franciscana exhibits several chromocenters in the resting nucleus, heterochromatic blocks located at the end of the prophase chromosomes, and a large amount of repetitive DNA (Alu I 110-bp fragments). The other Artemia sp. lacks chromocenters, heterochromatic blocks in the chromosomes, and the Alu I DNA. The two populations thus differ by a remarkable amount of repetitive DNA.The authors dedicate this paper to Professor Hans Bauer, on the occasion of his 80th birthday 相似文献
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