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  • 1
    Electronic Resource
    Electronic Resource
    Evolution of the genome size inAkodon (Rodentia, Cricetidae) (1983)
    Springer
    Journal of molecular evolution 19 (1983), S. 362-370 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF02101640
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  • 2
    Electronic Resource
    Electronic Resource
    Sperm-chromatin maturation in the mouse (1986)
    Springer
    Histochemistry and cell biology 84 (1986), S. 484-491 
    Details
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Cytochemical techniques were used to study chromatin during spermiogenesis and sperm maturation in the mouse, starting from the stages at which the substitution of somatic histones by testis-specific proteins occurs. It was possible to distinguish and analyze the different temporal incidence of two processes involved in sperm maturation, i.e. chromatin condensation (a tridimensional highly compacted arrangement) and chromatin stabilization (a tough structure, which protects the genome DNA). The first process, involving a reduction in the nuclear size and a decrease in the amount of sperm DNA accessible to specific cytochemical reactions and stainings, was found to reach its maximum in caput-epididymidis spermatozoa, in which electron microscopy revealed that the sheared chromatin was mainly organized into 120-Å-thick knobby fibers. No further changes were found in sperm up to their appearance in the fallopian tubes. On the contrary, chromatin stabilization, the onset of which occurs in the testis (at the late spermatid stage) via the formation of -S−S- cross-links, is completed in the vas deferens, where chromatin has a superstructure consisting of thicker fibers, with diameters of 210 and 350 Å. The reductive cleavage of disulfides in vas-deferens spermatozoa does not completely destroy the superstructure of sperm chromatin, which could indicate ‘coiling’ of the basic knobby fiber. In fact, when the ion concentration was increased, the chromatin of vas-deferens spermatozoa appeared to be organized into fibers with diameters similar to those of the caput epididymidis. This unique organization of mature sperm chromatin should have an essential role in the fast swelling of spermatozoa during fertilization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00482981
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  • 3
    Electronic Resource
    Electronic Resource
    Feulgen-DNA amounts and karyotype lengths of three planarian species of the genusDugesia (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 75-77 
    Details
    ISSN: 1420-9071
    Keywords: Cytotaxonomy ; genome size ; karyotype length ; nuclear DNA amount ; planarians
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Genome sizes of the planariansD. lugubris (2n=8),D. polychroa (2n=8) andD. benazzii (2n=16) were evaluated on metaphase plates by measuring both the Feulgen-DNA contents and the karyotype lengths. In the three species, genome sizes are significantly different; this finding rules out the possibility of a karyotype evolution through simple chromosome rearrangements betweenD. lugubris andD. polychroa. A different Feulgen-DNA content per unit length of karyotype in the three species studied was also found, which suggests that DNA could be differently packed along metaphase chromosomes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01975903
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  • 4
    Electronic Resource
    Electronic Resource
    Osservazioni sull'istochimica della corda dorsale diLampetra planeri Bl. (1956)
    Springer
    Cell & tissue research 45 (1956), S. 280-303 
    Details
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Riassunto A conclusione di una vasta ricerca istochimica compiuta sulla corda dorsale diLampetra planeri adulto e allo stadio diAmmocoetes al massimo di accrescimento l'A. ha potuto dimostrare: a) la presenza di glicogeno nelle cellule cordali; b) la presenza di un mucopolisaccaride e di una proteina in rapporti abbastanza costanti (probabilmente costituenti un complesso mucoproteico) nel citoplasma delle cellule dello strato epiteliomorfo, nella guaina fibrosa e nella lamina interna della guaina elastica; c) 1'esistenza di gradienti di concentrazione di sostanza secca sia all'interno del tessuto cordoide propriamente detto, sia nello spessore delle guaine. Si prospetta la possibilità di inquadrare il complesso corda-guaine, prescindendo dalla sua origine embrionale, fra i tessuti connettivi, considerando come sostanza intercellulare la sostanza costituente le guaine. L'A. fa inoltre alcune considerazioni morfomeccaniche ed istofunzionali sulla struttura della corda.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01106082
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  • 5
    Electronic Resource
    Electronic Resource
    Genome size and «C-heterochromatic-DNA» in man and the african apes (1990)
    Springer
    Human evolution 5 (1990), S. 261-267 
    Details
    ISSN: 1824-310X
    Keywords: Hominoidea ; C-heterochromatin ; genome size ; flow cytometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The genome sizes and the amounts of DNA after C-banding pretreatments (C-heterochromatic DNA) were measured by quantitative cytochemical methods in man and the African apes,Gorilla gorilla andPan troglodytes. As evaluated by flow cytometry on propidium-iodide-stained lymphocytes, gorilla and chimpanzee have genome sizes larger than man. On the basis of the different resistance of metaphase chromosome DNA to the C-banding procedure, two genome compartments were defined, i.e.,C-heterochromatic-DNA andeuchromatic-DNA. The latter proved to be fairly constant in man and the African apes (as well as in two hylobatid species), whereas the variable amounts ofC-heterochromatic-DNA account well for the interspecific differences of genome size among the hominoid species studied so far. During karyotype diversification, quantitative changes (with either gains or losses) ofC-heterochromatic-DNA seem to have taken place independently in the hylobatid and the man/African ape lineages.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02437242
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  • 6
    Electronic Resource
    Electronic Resource
    The effect of different fixatives on chromatin: Cytochemical and ultrastructural approaches (1981)
    Springer
    Journal of molecular histology 13 (1981), S. 763-779 
    Details
    ISSN: 1573-6865
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary This study explores the effects of two types of fixative on chromatin. The first type (acrolein, glutaraldehyde) engenders a high degree of ultrastructural preservation. The other type are fixatives that are widely used in cytochemistry and cytogenetics (acetic acid, 3∶1 by vol. methanol-acetic acid, methanol alone, formaldehyde). Lymphocytes of adult rats so-fixedin vitro were prepared for electron microscopy or microdensitometric evaluations of smears. Assessments were made of variations in their total protein, nuclear basic protein and DNA contents. DNA was determined both as Feulgen-positive material and by its binding of intercalating dyes (Methyl Green, specific for double-stranded polynucleotides). Our results showed that some fixatives break up the chromatin organization by acting on particular components of chromatin fibres. They can thus be considered to be destructive agentsin situ. In addition, a revaluation of some aldehyde fixatives is proposed for both ultrastructural and cytochemical research.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01003288
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