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  • 1
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Sister chromatid cores, kinetochores and the connecting strand between sister kinetochores were differentially silver stained to analyse the behaviour of these structures during meiosis in normal and two spontaneous desynaptic individuals of Chorthippus jucundus (Orthoptera). In these desynaptic individuals most of the chromosomes appear as univalents and orient equationally in the first meiotic division. Despite this abnormal segregation pattern, the changes in chromosome structure follow the same timing as in normal individuals and seem to be strictly phase dependent. Chromosomes in the first prometaphase have associated sister kinetochores and sister chromatid cores that lie in the chromosome midline; we propose that this promotes the initial monopolar orientation of chromosomes. However, the requirements of tension for stable attachment to the spindle force the autosomal univalents to acquire amphitelic orientation. Sister kinetochores behave in a chromosome orientation-dependent manner and, in the first metaphase, they appear to be interconnected by a strand that can be detected by silver impregnation, as seen in the second metaphase of wild-type individuals. The disappearance of the sister kinetochore-connecting strand, needed for equational chromatid segregation, however, can only take place in the second meiotic division. This connecting strand is ultimately responsible for the inability of chromosomes to segregate sister chromatids in the first anaphase.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A detailed analysis, using a modified silver staining technique which permits the visualization of the chromatid cores in bivalents at metaphase I, shows that some so-called chromosome associations are indeed true chiasmata. This study employs a supernumerary segment on the longest of the autosome pairs in the grasshopper Chorthippus jucundus that produces clear asymmetric bivalents in heterozygotes. Clear evidence of crossing over within the supernumerary segment explains part of the polymorphism of this segment, since unequal crossing over can produce different-sized segments. The origin of this segment and its mode of inheritance are also considered in the light of these results.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An analysis of chiasma distribution in the nucleolar chromosomes of the grasshopperSphingonotus coerulans (L.) by means of silver staining revealed an underlying tendency for chiasmata not to be formed in the NORs. The possible meaning of this finding for the intact preservation of these regions through generations is discussed.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-6849
    Keywords: Chorthippus parallelus ; chromosome organization ; DNase I sensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have analysed the patterns of DNase I/nick translation in the chromosomes of the grasshopperChorthippus parallelus erythropus. Sites of preferential DNase I-nicking were concentrated at the distal chromosome regions, thus showing the non-uniform DNase I sensitivity of different chromosome domains. Among centromeric C-bands, the heterochromatin of metacentric and acrocentric chromosomes differed with respect to their DNase I resistance.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A spontaneous structural heterozygote originated from a centric fusion involving two acrocentric autosomes (M5 and S8) in a male Chorthippus jucundus (2n=16+X) was tested for the effects on chiasmata characteristics and the role that these could play in metaphase-I orientation of the trivalent. Results show non-existence of inter- or intra-chromosomal effects on chiasma frequency when compared with standard individuals, and displacement of the single chiasma on the S8 to a distal position while no significant change is appreciated in the M5 chiasma distribution. The presence of two chiasmata on the M5 and one on the S8 always induces a linear orientation of the trivalent. However, when two chiasmata are present (one on each chromosome) and independently of their location on each arm (proximal, interstitial of distal) any of the possible orientations (linear or convergent) can be attained. The frequency of linear orientation is higher than that expected at random in the resulting trivalent during metaphase-I and the rate of reorientation is very low. The meitotic behaviour of such a trivalent is discussed taking into account the already mentioned aspects together with the size of the fused element.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The analysis of 18 wild populations of the polymorphic species Chorthippus jucundus has revealed the presence of five distal extra segments. They differ in location, size and staining properties. Two of them (L1H and L1h) are located in the largest element and do not C-band, while the remainder (S8H, S8h and S8h1) appear in the shortest chromosome and show positive C-banding. Those located in the same chromosome differ basically in their size. However, any of these blocks induce a similar change in the pattern of chiasma distribution within the affected bivalent. Additionally four patterns of C-banding as regards the presence of distal bands in some autosomes have been detected in the different populations.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Genetica 79 (1989), S. 27-35 
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Several individuals from distinct populations of 7 subspecies included in the Triturus alpestris complex have been analysed to obtain characteristic C-banding patterns. The differences found among the populations as regards the amount, complexity and distribution of heterochromatin bands have been employed to test a pattern of chromosome evolution. Relevant similarities and dissimilarities of these populations are discussed in the light of the tentative evolutionary history inferred from a rooted tree.
    Type of Medium: Electronic Resource
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