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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Cellular and molecular life sciences 38 (1982), S. 792-794 
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary When cells were irradiated with variable doses of gamma rays, 0.33% showed the appearance of single decondensed chromosomes (SDC) at the moment at which all the other chromosomes of the complement exhibited the normal condensed state corresponding to metaphase stages. Several hypotheses are discussed to explain the origin of SDC. It appears that the most reasonable mechanism to explain our observations is to assume that the process of chromosome condensation is independently controlled in each individual chromosome by a gene/s located in each one of the chromosomes of the complement. A radiation-induced deficiency in one of these genes may produce an impairement in the normal process of condensation of the carrier chromosome which would give rise to SDC.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Algorithmica 22 (1998), S. 112-137 
    ISSN: 1432-0541
    Keywords: Key words. Boolean prediction, On-line algorithms, Bayes theory.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. We examine a general Bayesian framework for constructing on-line prediction algorithms in the experts setting. These algorithms predict the bits of an unknown Boolean sequence using the advice of a finite set of experts. In this framework we use probabilistic assumptions on the unknown sequence to motivate prediction strategies. However, the relative bounds that we prove on the number of prediction mistakes made by these strategies hold for any sequence. The Bayesian framework provides a unified derivation and analysis of previously known prediction strategies, such as the Weighted Majority and Binomial Weighting algorithms. Furthermore, it provides a principled way of automatically adapting the parameters of Weighted Majority to the sequence, in contrast to previous ad hoc doubling techniques. Finally, we discuss the generalization of our methods to algorithms making randomized predictions.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1432
    Keywords: Zfy-Zfx genes ; Gene evolution ; Oryzomyne-akodontine rodents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Zinc finger-Y (Zfy) and zinc finger-X (Zfx) genes were analyzed by Southern blotting in male and female specimens of 10 species belonging to the oryzomyne-akodontine stock of Cricetidae rodents. DNA fragments were used as characters to construct a parsimony tree of the genes. Zfx and Zfy trees in general coincide with the evolutionary history of the taxa. Both trees show Oryzomys longicaudatus genes as the outgroup whereas Akodon xanthorrhinus genes are also distant from those of the other species. Oxymycterus rufus and Bolomys obscurus share related sequences, while genes from the other six Akodon species form a group of their own. It was found that 9 out of the 10 species analyzed show Zfy amplification in a range varying from 2 to 24 copies and with a pattern that is clade specific. The estimation of the average changes per character strongly suggests that Zfy has evolved more rapidly than Zfx; our estimates of the rate of nucleotide substitution are 4.6 times higher for Zfy than for Zfx.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1432
    Keywords: Pongidae ; Chromosome ; Karyotype ; Restriction enzymes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The pattern of banding induced by five restriction enzymes in the chromosome complement of chimpanzee, gorilla, and orangutan is described and compared with that of humans. The G banding pattern induced by Hae III was the only feature common to the four species. Although hominid species show almost complete chromosomal homology, the restriction enzyme C banding pattern differed among the species studied. Hinf I did not induce banding in chimpanzee chromosomes, and Rsa I did not elicit banding in chimpanzee and orangutan chromosomes. Equivalent amounts of similar satellite DNA fractions located in homologous chromosomes from different species or in nonhomologous chromosomes from the same species showed different banding patterns with identical restriction enzymes. The great variability in frequency of restriction sites observed between homologous chromosome regions may have resulted from the divergence of primordial sequences changing the frequency of restriction sites for each species and for each chromosomal pair. A total of 30 patterns of banding were found informative for analysis of the hominid geneaalogical tree. Using the principle of maximum parsimony, our data support a branching order in which the chimpanzee is more closely related to the gorilla than to the human.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 19 (1983), S. 362-370 
    ISSN: 1432-1432
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nuclear DNA contents were estimated by microdensitometry in five species ofAkodon rodents:Adodon molinae, A. dolores, A. mollis, A. azarae, Bolomys obscurus) and in three chromosomal varieties ofA. molinae (2n=42; 2n=43, 2n=22). The data obtained showed that the species with the highest DNA content wasB. obscurus, followed in order of decreasing genome size byA. molinae, A. mollis, A. dolores andA. azarae. InA. molinae the forms with 2n=42 chromosomes had the lowest and the forms with 2n=44 the highest amount of DNA, while the forms with 2n=43 had intermediate DNA contents. The variation in DNA amount detected inA. molinae was interpreted as a phenomenon of amplification occurring in the chromosomal areas involved in the chromosomal rearrangement giving rise to the polymorphism exhibited by this species. The DNA contents of shared chromosomes (chromosomes with similar size, morphology and G banding pattern, which are found in two or more phylogenetically related species), were compared and correlated with values of total nuclear DNA. The information obtained indicates that: (a) shared chromosomes have variable amounts of DNA: (b) in a given species there is a correlation between the amount of nuclear and chromosomal DNA in most shared chromosomes (and perhaps in most of the chromosmal complement), e.g., the higher the amount of nuclear DNA, the higher the content of DNA in shared chromosomes; (c) some chromosomes may undergo processes of amplification or deletion restricted to certain regions and usually related with mechanisms of chromosomal rearrangements. The data obtained seem to indicate that the genome size of a species depends on the interaction of two independent mechanisms: (1) a general process of DNA variation which acts coincidentally in the same direction (gain or loss) in the whole chromosome complement without disturbing the mechanism of chromosome condensation producing G bands and (2) restricted processes of DNA variations (amplifications or deletions) which act on single chromosomes and which are in most cases related with chromosmal rearrangements.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 22 (1967), S. 391-400 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The morphology and pattern of replication in the somatic chromosomes of Leptodactylus ocellatus (Amphibia, Anura) was studied by means of H3-thymidine autoradiography. A total of 300 metaphases from leukocyte cultures and 200 metaphases from spleen cell cultures were analysed. The diploid chromosome number in Leptodactylus ocellatus is 22. The pairs 1, 2, 3, 4, 7 and 8 could be easily identified on the basis of their size, centromere position, and location of secondary constrictions. In 30% of metaphases the pair 10 could be recognized on account of an end-to-end homologous association, which originated from a satellite fusion. The continuous H3-thymidine labelings carried out in the last 10, 5 and 3 hours of a culture indicated that the G2 period was 3.5 hours. The labeled metaphases were divided in two groups. In the first one all those cells showing radioactivity along the entire length of every chromosome were included. The second group was formed by metaphases with extensive unlabeled chromosome regions. The former and the latter group were identified as representatives of the intermediate and final stages of the S period, respectively. The pattern of chromosome labeling indicates that secondary constrictions are associated with late replicating regions. However, the presence of chromosome areas, which in spite of being late in finishing duplication did not bear any kind of constriction, suggests that regions other than those associated with constrictions also may replicate late. No interchromosomal asynchrony of replication at the end of the S period was noticed. However, very often in pair 10 one chromosome had about two times as much labeling as its homologue. No sex-linked differences in chromosome morphology or in patterns of chromosome replication could be noticed.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Chromosome measurements were performed in four species of snakes related at the level of suborder (Boa constrictor amarali, Xenodon merremii, Philodryas patagoniensis, Bothrops jararaca). The data obtained point out that pairs 1–3 were common to the four snakes and probably inherited from the ancestor of the suborder Serpentes. Pairs 5–8-W were characteristic of each snake; hence, it is possible to assume that they followed evolving after the appearing of the suborder Serpentes. Z-chromosomes were metacentric in B. constrictor amarali, X. merremii and B. jararaca and slightly submetacentric in P. patagoniensis. Area of these chromosomes varied from 8.6–10.6% of the haploid set in the four species studied.-The study of chromosome replication at the end of the S period points out that “shared chromosomes” have similar patterns of labeling. Therefore, it is proposed that the distribution of late replicating regions and heterochromatin in the genome is phylogenetically transmitted and probably genetically determined.—The analysis of the ending-sequence of chromosome replication shows that sex chromosomes finish earlier than macroautosomes. It is concluded that snakes probably have no mechanism of sex chromosome heterochromatinization in either sex. The absence of late replicating Z-chromosome in the males, favours the hypothesis that no mechanism of sex dosage compensation is acting in the suborder Serpentes.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 28 (1969), S. 370-378 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The chronology of Y chromosome replication in meiosis of male adult rats was investigated. 3HTdR was injected into the testes and animals were sacrificed at 2-hour intervals from 2 to 24 hour after the injection; and at 2-day intervals from 2 to 64 days after the injection. Autoradiograms from germ line cell spreads were prepared. The study of spermatogonial metaphases showed that the Y chromosome is the last to begin and end DNA synthesis. Consequently, by detecting such a pattern of replication it was possible to trace the asynchronous Y from spermatogonia to sperm. Assuming that Y chromosomes are early replicating in preimplantation embryos of mammals it is proposed that Y chromosome of rats shift from late to early replicating in the first divisions of the fertilized egg. Moreover, the analysis of the patterns of sperm labeling allow one to infer that chromosomes are end-to-end associated in sperm nuclei, and that the Y chromosome and perhaps autosomes as well occupy a constant position in sperm of rats.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Bradford : Emerald
    Compel 20 (2001), S. 777-795 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The optimisation of a tubular linear motor with interior permanent magnets is described. For a rapid design the whole process is divided in three parts: an analytical approach for the a preliminary investigation, a parametric analysis by means of a finite element method and an optimisation. The obtained results show that the adopted optimisation process is efficient for rapid and effective optimisation of the tubular linear motor.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0375-9474
    Keywords: Nuclear reactions
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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