Showing papers in "Chromosoma in 1970"
TL;DR: A convenient measuring technique has been developed for the rapid and accurate recording of fluorescence patterns in human metaphase chromosomes that should be particularly valuable for the identification of chromosomes 4–5 and the individual types in the 6–12 group.
Abstract: The distribution of DNA along metaphase chromosomes that are not excessively contracted can be visualized in the fluorescence microscope with the aid of fluorescent DNA-binding agents. Additional, characteristic details in the fluorescence patterns are obtained with fluorochromes that bind preferentially to certain chromosomal regions. The highly fluorescent alkylating agent quinacrine mustard (QM) effects discrete, fluorescent labeling of both plant and mammalian metaphase chromosomes, presumably by selective binding to guanine residues in DNA, and is also capable of intercalation in the DNA double helix. Chromosome regions fluorescing particularly strongly with QM have been demonstrated in human metaphase chromosomes 3, 13–15 and Y. A convenient measuring technique has been developed for the rapid and accurate recording of fluorescence patterns in human metaphase chromosomes. These photoelectric recordings of the fluorescence patterns contain far greater detail than can be seen by the human eye. The fluorescence patterns described are based on measurements of about 1,000 human metaphase chromosomes. This new technique of determining fluorescence patterns in human chromosomes should be particularly valuable for the identification of chromosomes 4–5 and the individual types in the 6–12 group. Individual, typical patterns also occur within the groups 13–15, 17–18, and 21–22.
919 citations
TL;DR: It is shown that in Drosophila hydei the ribosomal cistrons are located within the nucleolus and in Rhynchosciara hollaenderi and Sciara coprophila, DNA coding for Ribosomal RNA is present both in theucleolus organizer regions of the chromosomes and in micronucleoli scattered throughout the nucleus.
Abstract: Molecular hybridization of radioactive ribosomal RNA with the DNA of cytological preparations is used to study the distribution of the ribosomal cistrons within the polytene chromosomes of three species of Diptera. It is shown that in Drosophila hydei the ribosomal cistrons are located within the nucleolus. In Rhynchosciara hollaenderi and Sciara coprophila, DNA coding for ribosomal RNA is present both in the nucleolus organizer regions of the chromosomes and in micronucleoli scattered throughout the nucleus. The DNA puffs in the salivary chromosomes of these sciarid flies do not contain detectable quantities of ribosomal cistrons. — RNA prepared by in vitro transcription has also been used to localize the ribosomal cistrons in Rhynchosciara. — Modifications in the technique of cytological hybridization are discussed.
253 citations
TL;DR: A similar pattern of induced puffs to that found after temperature treatment is found during recovery of larvae from anoxia, but additional puffs are “induced” after anoxion, and the size and duration of activity of the induced puffed is dependent upon the magnitude of the treatment.
Abstract: Exposure of Drosophila melanogaster larvae to high temperature for short periods of time results in marked changes in the puffing patterns of salivary gland chromosomes. Temperature shock "induces" puffing at 9 specific loci; this pattern of induced puffs shows little developmental specificity and is similar in three strains of D. melanogaster (including the mutant lethal giant-larvae) and in D. simulans. Temperature shock also (i) retards the regression of some devel- opmentally specific puffs and (ii) results in the regression of all other puffs normal to development. The effect of temperature treatment is similar in vivo and after in vitro treatment of salivary glands. The in vitro response is not sensitive to cycloheximide. A similar pattern of induced puffs to that found after temperature treatment is found during recovery of larvae from anoxia, but additional puffs are "induced" after anoxia. The size and duration of activity of the induced puffs is dependent upon the magnitude of the treatment.
243 citations
TL;DR: It has been shown that two cores exist in the sex pair and that their lengths and morphology are rather constant in specific stages, and the existence of a homologous region in the X-Y pair of the mouse is interpreted to be proved.
Abstract: The ultrastructure of whole X-Y pairs has been reconstructed by serial sectioning and model building. Seven X-Y pairs were completely reconstructed and the lengths of the cores of the sex chromosomes were measured. These X-Y pairs corresponded to zygonema, early, middle and late pachynema. Special regions of the X-Y pair were reconstructed from thinner sections. — It has been shown that two cores exist in the sex pair during the cited stages, and that their lengths and morphology are rather constant in specific stages. The long core averages 8.9 μ in length and the short core is 3.5 μ long. Both cores have a common end region in which a synaptonemal complex is formed from zygonema up to midpachynema. This synaptonemal complex shortens progressively up to mid-pachynema and at late pachynema becomes obliterated. Each core has a free end touching the nuclear membrane. During mid-pachynema an anomalous synaptonemal complex is developed on most of the length of the long core. This complex is asymmetric and disappears at late pachynema. The meaning of the cores and the complexes are discussed, and the existence of a homologous region in the X-Y pair of the mouse is interpreted to be proved.
152 citations
TL;DR: Renaturation studies support various evidence that satellite sequences occur in tandemly repetitious units and at least some of this repetitious material seems to be linked to non-satellite DNA sequences or to DNA of other satellites.
Abstract: It is shown by isopycnic density gradient centrifugation that the DNAs of the sibling species Drosophila hydei, Drosophila neohydei and Drosophila pseudoneohydei differ regarding the numbers and proportions of satellite DNA bands. An overwhelming proportion of all repetitive nucleotide sequences of the DNA is contained in these satellite fractions. The majority of the satellites are species specific despite the close phylogenetic and cytological relationship between the three species studied. — By in situ hybridization experiments it is demonstrated that the various satellite sequences occupy different positions within the chromosomes. All types of localization patterns, from a wide spread occurrence in all chromosomes to an apparent restriction to kinetochore regions of single chromosomes, have been observed. Main band DNA, on the other hand, in its hybridization behavior reflects the DNA distribution according to the banding pattern in giant chromosomes. Generally satellite sequences seem to be included in α-heterochromatic chromosome regions but no relation to the heterochromatin of the Y-chromosome was found. — Renaturation studies support various evidence that satellite sequences occur in tandemly repetitious units. At least some of this repetitious material seems to be linked to non-satellite DNA sequences or to DNA of other satellites.
135 citations
TL;DR: It is inferred that both in mouse and Drosophila the centromeric regions of all chromosomes are enriched in highly reiterated sequences, which might play some role in promoting the close physical approximation of homologous and non-homologous chromosomes or chromosome regions to facilitate regulation of function.
Abstract: The location of highly reiterated nucleotide sequences on the chromosomes has been studied by the technique of in situ hybridisation between the DNA of either Drosophila melanogaster salivary gland chromosomes or mouse chromosomes and tritium labelled complementary RNA (c-RNA) transcribed in vitro from appropriate templates with the aid of DNA dependent RNA polymerase extracted from Micrococcus lysodeikticus. The location of the hybrid material was identified by autoradiography after RNase treatment. — When Drosophila c-RNA, transcribed from whole DNA, was annealed with homologous salivary chromosomes in the presence of formamide the well defined labelling was confined to the chromocentre. With heat instead of formamide denaturation there was evidence of discontinuous labelling in various chromosome regions as well, apparently associated with banding. Xenopus ribosomal RNA showed no evidence of annealing to Drosophila chromosomes with the comparatively short exposure times used here. — When mouse satellite DNA was used as template the resulting c-RNA showed no hybridisation to Drosophila chromosomes but, when annealed with mouse chromosomes, the centromeric regions were intensely labelled. The interphase nuclei showed several distinct regions of high activity which suggested aggregation of centromeric regions of both homologous and non-homologous chromosomes. The results of annealing either c-RNA or labelled satellite DNA to homologous chromosomes were virtually indistinguishable. Incubation of Drosophila c-RNA with mouse chromosomes provided no evidence of localisation of grains. — It is inferred that both in mouse and Drosophila the centromeric regions of all chromosomes are enriched in highly reiterated sequences. This may be a general phenomenon and it might be tentatively suggested that the highly reiterated sequences play some role in promoting the close physical approximation of homologous and non-homologous chromosomes or chromosome regions to facilitate regulation of function.
122 citations
TL;DR: Some types of acridine derivative and especially Quinacrine dihydrochloride and its mustard may be successfully used as chromosome marker and to investigate the chemical differentiation of euchromatin and heterochromatin.
Abstract: Some types of acridine derivative and especially Quinacrine dihydrochloride and its mustard may be successfully used as chromosome marker and to investigate the chemical differentiation of euchromatin and heterochromatin. — There are at least four main types of heterochromatin, showing all possible combinations of positive and negative cold effect “starvation” (St. + or St. -) and enhanced or reduced fluorescence (Fl. + or Fl. -). —The relationship between the four different classes of heterochromatin is not yet clear.
120 citations
TL;DR: Chromosome pairing takes two steps: members of the homologous pair become aligned first and then “zip up” throughout their length, followed by a diffuse stage in which the chromosomes are most indistinct.
Abstract: Chromosome pairing takes two steps: members of the homologous pair become aligned first and then “zip up” throughout their length. Initial contact may begin from one end or from both ends of the chromosomes. Prom late paehytene to diplotene, the chromosomes are somewhat elongated and exhibit lampbrush characteristics. This is followed by a diffuse stage in which the chromosomes are most indistinct. The centrosome divides at this time. The chromosome numbers are as follows: Coprinus lagopus, n=12; C. micaceus, n=12, C. comatus, n=14; and C. atramentarius, n=16.
120 citations
TL;DR: It was possible to observe that the sporal wall of each spore originated from the same unique double membrane formed in the ascus during the meiotic second division and postmeiotical mitosis.
Abstract: The behaviour of the division spindle and centrosomal plaques is described in four species of Ascomycetes (Ascobolus immersus, Ascobolus stercorarius, Podospora anserina and Podospora setosa) studied by light and electron microscopy. Two unique features of the kinetical apparatus were observed: presence of centrosomal plaques and intranuclear location of the spindle. In all types of mitoses (mycelium, crosier and postmeiotical mitosis) the apparatus is structurally identical to that found in meiosis. The centrosomal plaques, present in all divisions, are always contiguous with the nuclear envelope and never show centrioles similar to those commonly found in Metazoa and Protozoa. During metaphase and anaphase the plaque is constituted of two zones situated on each side of the nuclear envelope: an electron opaque outer zone and inner one less opaque in which most of the microtubules end. In Podospora the outer zone appears in sections as consisting of two dark layers separated by a clear one. Two dispositions of plaques are possible: either they are entirely contiguous with the nuclear envelope (Ascobolus) or only partially so, the remainder being perpendicular to the nuclear envelope (Podospora). — The localisation of the plaques in the ascus was determined by light and electron microscopy. The nuclear envelope was shown to remain intact during division. It was possible to observe that the sporal wall of each spore originated from the same unique double membrane formed in the ascus during the meiotic second division and postmeiotical mitosis. This fact is of genetical interest for the study of morphological and physiological characters of the spores.
107 citations
TL;DR: Since the morphological features of the central element of the synaptonemal complex persist despite extensive deoxyribonuclease digestion, pairing is perhaps best visualized as a two-step process consisting of a) chromosomal pairing during which the proteinaceous synaptic complex pulls homologous chromosomes into approximate association with each other, and b) molecular pairing, which probably takes place in the area around the synapses.
Abstract: The mechanism by which homologous chromosomes pair and crossover has been a major unsolved problem in genetics. Thin section electron microscopy of the synaptonemal complex has not provided enough details to allow any significant insight into this problem. Whole mount preparations of the testis of mice, quail, crayfish, and frogs provided a striking improvement in visualization of the morphological features of meiotic chromosomes. These studies, when combined with the use of deoxyribonuclease and trypsin allowed the following conclusions. 1. The synaptonemal complex (lateral and central elements with connecting L-C fibers) is composed of protein. 2. Contrary to common speculation the central element is not the pairing surface of homologous chromosomes. 3. The L-C fibers, averaging 75–100 A in width, extend from the lateral elements and meet to form the central element which is usually composed of four fibers. 4. During leptotene, homologous axial elements, although unpaired for most of their length, attach next to each other at the nuclear membrane. 5. Short segments of the chromatin fibers attach to the lateral elements. These points of attachment are clustered, producing the chromomeres seen by light microscopy. 6. The chromatin fibers extend out from the lateral element as loops. Lampbrush chromosomes are thus not restricted to oogenesis but are common to all meiotic chromosomes. Since the morphological features of the central element of the synaptonemal complex persist despite extensive deoxyribonuclease digestion, pairing is perhaps best visualized as a two-step process consisting of a) chromosomal pairing during which the proteinaceous synaptonemal complex pulls homologous chromosomes into approximate association with each other, and b) molecular pairing, which probably takes place in the area around the synaptonemal complex.
104 citations
TL;DR: Meiosis in the male mouse has been studied autoradiographically in air-dried preparations and the labelling pattern of the sex-chromosomes and autosomes observed at diakinesis and metaphase II in cells labelled at the spermatocyte S-period appears to be similar to that found during the sPermatogonial S- period.
Abstract: Meiosis in the male mouse has been studied autoradiographically in air-dried preparations. Information has been obtained on the relative rates of DNA synthesis and the lengths of the S-periods in spermatogonia and spermatocytes. The average rate of synthesis in the spermatocyte is lower, and the S-period is of longer duration than the preceding spermatogonial generations. The labelling pattern of the sex-chromosomes and autosomes observed at diakinesis and metaphase II in cells labelled at the spermatocyte S-period appears to be similar to that found in cells labelled during the spermatogonial S-periods. Replication in the autosomes commences before the sex-chromosomes. Late replicating autosomal centric regions show a marked degree of asynchrony in labelling both between and within bivalents. The Y chromosome starts and finishes replication later than the X. There is a short, late-replicating, segment of the X in the vicinity of the centromere. There is a short, early-replicating segment of the Y in the vicinity of the centromere which may represent the euchromatic short arm. The X and Y appear to associate at diakinesis by the distal ends of their long arms.
TL;DR: It is supposed that in addition to the duplication of structural DNA an extra DNA is synthesized which disappears immediately from the chromosome at the end of the replication cycle in the salivary gland nuclei of the hybrid Chironomus th.
Abstract: The pattern of DNA-synthesis of the salivary gland chromosomes of Chironomus thummi thummi, Ch. th. piger, Ch. annularius, Ch. plumosus and Ch. melanotus was studied using H3-thymidine-autoradiography. Contrary to the previous conception the bands of the salivary gland chromosomes of Chironomus do not begin replication simultaneously. H3-thymidine incorporation in bands of high DNA content begins later than in bands with a lesser amount of DNA. This difference in time is very small in bands outside the kinetochore regions and not comparable to the asynchrony in replication of typical heterochromatin in the salivary gland chromosomes of Chironomus melanotus. Differences in the amount of DNA in homologous bands do not affect the onset of replication. — Bands of high DNA content are replicating during a longer time than those having less DNA. However, certain chromosome regions behave differently. In these regions bands of very low DNA content are synthesizing DNA during the whole replication cycle. Since no excessive increase of DNA could be observed in these regions it is supposed that in addition to the duplication of structural DNA an extra DNA is synthesized which disappears immediately from the chromosome. — At the end of the replication cycle in the salivary gland nuclei of the hybrid Chironomus th. thummi X Ch. th. piger a labeling pattern is found in the chromosomes of Ch. th. thummi which differs from that in the parental subspecies Ch. th. thummi.ZusammenfassungDer Verlauf der DNS-Synthese in den Speicheldrüsen-Chromosomen von Chironomus thummi thummi sowie anderer Chironomus-Arten wurde mit Hilfe der H3-Thymidin-Autoradiographie untersucht. Dabei ergaben sich gegenüber den bisher bekannten Befunden folgende neue Resultate:1.Bei Ch. th. thummi beginnt die DNS-Synthese nicht wie bisher angenommen in allen Querscheiben und den Zwischenscheibenregionen gleichzeitig. Am Anfang des Replikationsschritts steht vielmehr eine kurze Phase, in der bestimmte Querscheiben mit hohem DNS-Gehalt — dazu gehören auch Strukturen der Kinetochorregionen — nicht replizieren.2.Die bisherige Annahme, daß die Querscheiben stets in bestimmter Reihenfolge die DNS-Synthese beenden, kann in dieser strengen Formulierung nicht aufrecht erhalten werden. Zwar gilt weiterhin, daß Querscheiben mit hohem DNS-Gehalt länger replizieren als DNS-ärmere, doch wird die darauf basierende Reihenfolge in Einzelfällen auch ohne feststellbaren Grund verändert.3.Während der Endphase des Replikationsschritts, an der nach den bisherigen Befunden ausschließlich die Querscheiben der Kinetochorregionen beteiligt sein sollen, konnte an bestimmten interkalaren Querscheibengruppen von Chromosom II (A2j-A3(d); E1g; E2c) und III (A3a; B3n) H3-Thymidin-Einbau festgestellt werden. Der geringe DNS-Gehalt dieser Chromosomen-Abschnitte steht im klaren Mißverhältnis zu der beanspruchten Replikationsdauer. Für die Erscheinung gibt es zur Zeit nur die Erklärung, daß durch Extra-DNS-Synthesen nach erfolgter Verdopplung der betreffenden Strukturen zusätzlicher Thymidin-Bedarf eintritt. Da bisher keine disproportionierte Erhöhung des DNS-Gehalts dieser Abschnitte nachgewiesen werden konnte, muß angenommen werden, daß die überschüssige DNS von den Chromosomen sogleich wieder abgegeben wird. Der an seinem Querscheibenmuster leicht identifizierbare Abschnitt A2j-A3(d) in Chromosom II zeigt auch bei anderen Chironomus-Arten (Ch. annularius; Ch. plumosus; Ch. melanotus) das gleiche Replikationsverhalten.4.Die Querscheiben der Kinetochorregionen von Ch. th. thummi beenden die Replikation in einer bevorzugten Reihenfolge, bei der Chromosom IV den Abschluß macht. Im Bastard von Ch. th. thummi X Ch. th. piger ist die Reihenfolge verändert. In diesem Fall markiert die alleinige Replikation der Kinetochorregion von Chromosom III die Schlußphase.5.An den Heterochromatin-Blöcken der Speicheldrüsen-Chromosomen von Chironomus melanotus wurde der für Heterochromatin typische asynchrone Replikationsablauf festgestellt. Die offen bleibende Frage, inwieweit die geringe Asynchronie beim Replikationsbeginn in den Kinetochor- und Interkalarstrukturen der Speicheldrüsen-Chromosomen von Ch. th. thummi eine funktionelle Annäherung an eine echte Heterochromatinisierung einschließlich ihrer funktionellen Konsequenzen darstellt, wird diskutiert.
TL;DR: It has been inferred that the convergence regions represent chiasmata and that the single axes do not represent axial structures of chromatids.
Abstract: The fate of the synaptonemal complex and its elements after pachytene has been studied by serial sectioning of diplotene nuclei in mouse spermatocytes. The lateral elements of the synaptonemal complex separate from each other during diplotene, and they form single axes, 300 A wide, surrounded by chromatin fibrils. The single axes are continuous and end on the nuclear membrane by two different ends: the basal knob and the simple end. The single axes do not cross-over each other, but they remain approached at the convergence regions. In these regions a modified piece of synaptonemal complex is found. This piece changes into a chromatin bridge during diplotene. It has been inferred that the convergence regions represent chiasmata and that the single axes do not represent axial structures of chromatids.
TL;DR: The available evidence points to the neo-XY system having evolved following a secondary movement of the species into the higher ground it now occupies after the climatic amelioration at the end of the last ice age.
Abstract: Populations of the alpine grasshopper Podisma pedestris are either completely XO/XX or else completely neo-XY/neo-XX in character. The neo-XY form is limited in its occurrence to near the extreme southwest edge of the present distribution of the species. Both kinds of population also contain B-chromosomes. These are of two types differing with regard to size, stability and origin. Both types can occur in the same population but have not so far been found in the same individual. The pattern of distribution of the larger, mitotically-stable supernumerary suggests that it might be a remnant X-chromosome which became converted into a B in the initial phase of neo-XY evolution. The smaller, partly unstable supernumerary, on the other hand, may well have originated from a heteromorphic S11 pair also found in some of the populations with small B's. The available evidence points to the neo-XY system having evolved following a secondary movement of the species into the higher ground it now occupies after the climatic amelioration at the end of the last ice age.
TL;DR: Electron microscopic observations on sections of squashed glutar-aldehyde-fixed salivary gland X-chromosomes of Drosophila melanogaster provided an ultrastructural map of the band sequence of region 1A1 to 4E3, which revealed a significantly lower number of bands.
Abstract: Electron microscopic observations on sections of squashed glutar-aldehyde-fixed salivary gland X-chromosomes ofDrosophila melanogaster provided an ultrastructural map of the band sequence of region 1A1 to 4E3. Comparison of this map with the map of Bridges (1938) revealed a significantly lower number of bands. Only 67% of the bands depicted in Bridges' map could be identified. This discrepancy seems to be a consequence mainly of the absence of doublet characters of bands on Bridges' map. — A possible relationship between bands and genes is discussed for some regions, including the white-Notch region. It appears that a one to one relationship between bands and genes does exist for two regions, whereas in region 3C1–3C7 more genes than bands are present. In this respect the structural organization of bands at the submicroscopic level is discussed. — The average DNA content of a band at the haploid level is calculated on the basis of the reduction in band number to be 4.5 × 10−5 picogram.
TL;DR: Observations support the classical view that synapsis of homologous chromosomes takes place during zygotene, followed by crossing-over at pachytene.
Abstract: A period of chromosome spiralization and contraction was observed between premeiotic interphase and leptotene in Lilium longiflorum “Croft”. There was variation in the extent of preleptotene spiralization and contraction of chromosomes among microsporocytes, anthers and buds. The chromosomes sometimes contracted sufficiently to be visible as separate entities. It could then be determined that the chromosomes were single and entirely separate; synapsis and crossing-over had not yet occurred. Furthermore there was no evidence of alignment or association of homologues during the preleptotene contraction period; the chromosomes appeared to be distributed at random. The chromosomes subsequently elongated into the leptotene stage. Wherever they were visible separately the chromosomes were single in early leptotene. These observations support the classical view that synapsis of homologous chromosomes takes place during zygotene, followed by crossing-over at pachytene.
TL;DR: In this paper, the DNS-Synthese in the Speicheldrusen-Chromosomen von Chironomus thummi thummmi et al. was untersucht in all Querscheiben and den Zwischenscheibenregionen.
Abstract: Der Verlauf der DNS-Synthese in den Speicheldrusen-Chromosomen von Chironomus thummi thummi sowie anderer Chironomus-Arten wurde mit Hilfe der H3-Thymidin-Autoradiographie untersucht. Dabei ergaben sich gegenuber den bisher bekannten Befunden folgende neue Resultate:
1.
Bei Ch. th. thummi beginnt die DNS-Synthese nicht wie bisher angenommen in allen Querscheiben und den Zwischenscheibenregionen gleichzeitig. Am Anfang des Replikationsschritts steht vielmehr eine kurze Phase, in der bestimmte Querscheiben mit hohem DNS-Gehalt — dazu gehoren auch Strukturen der Kinetochorregionen — nicht replizieren.
2.
Die bisherige Annahme, das die Querscheiben stets in bestimmter Reihenfolge die DNS-Synthese beenden, kann in dieser strengen Formulierung nicht aufrecht erhalten werden. Zwar gilt weiterhin, das Querscheiben mit hohem DNS-Gehalt langer replizieren als DNS-armere, doch wird die darauf basierende Reihenfolge in Einzelfallen auch ohne feststellbaren Grund verandert.
3.
Wahrend der Endphase des Replikationsschritts, an der nach den bisherigen Befunden ausschlieslich die Querscheiben der Kinetochorregionen beteiligt sein sollen, konnte an bestimmten interkalaren Querscheibengruppen von Chromosom II (A2j-A3(d); E1g; E2c) und III (A3a; B3n) H3-Thymidin-Einbau festgestellt werden. Der geringe DNS-Gehalt dieser Chromosomen-Abschnitte steht im klaren Misverhaltnis zu der beanspruchten Replikationsdauer. Fur die Erscheinung gibt es zur Zeit nur die Erklarung, das durch Extra-DNS-Synthesen nach erfolgter Verdopplung der betreffenden Strukturen zusatzlicher Thymidin-Bedarf eintritt. Da bisher keine disproportionierte Erhohung des DNS-Gehalts dieser Abschnitte nachgewiesen werden konnte, mus angenommen werden, das die uberschussige DNS von den Chromosomen sogleich wieder abgegeben wird. Der an seinem Querscheibenmuster leicht identifizierbare Abschnitt A2j-A3(d) in Chromosom II zeigt auch bei anderen Chironomus-Arten (Ch. annularius; Ch. plumosus; Ch. melanotus) das gleiche Replikationsverhalten.
4.
Die Querscheiben der Kinetochorregionen von Ch. th. thummi beenden die Replikation in einer bevorzugten Reihenfolge, bei der Chromosom IV den Abschlus macht. Im Bastard von Ch. th. thummi X Ch. th. piger ist die Reihenfolge verandert. In diesem Fall markiert die alleinige Replikation der Kinetochorregion von Chromosom III die Schlusphase.
5.
An den Heterochromatin-Blocken der Speicheldrusen-Chromosomen von Chironomus melanotus wurde der fur Heterochromatin typische asynchrone Replikationsablauf festgestellt. Die offen bleibende Frage, inwieweit die geringe Asynchronie beim Replikationsbeginn in den Kinetochor- und Interkalarstrukturen der Speicheldrusen-Chromosomen von Ch. th. thummi eine funktionelle Annaherung an eine echte Heterochromatinisierung einschlieslich ihrer funktionellen Konsequenzen darstellt, wird diskutiert.
TL;DR: Demonstration of cytogenetic criteria by which females from triploid clones may be clearly distinguished from sympatric diploid specimens of P. formosa or P. mexicana leaves unresolved, for the present, problems of an appropriate systematic designation for natural populations of Triploid gynogenetic fishes.
Abstract: Natural populations of triploid females resembling the gynogenetic teleost, Poecilia formosa (Girard), occur in northeastern Mexico where they intermingle with diploid populations of this species and the members of congeneric bisexual species such as P. mexicana or P. latipinna. Mitotic configurations from gill epithelial cells show 46 chromosomes for the diploid fishes, but 69 chromosomes for members of the triploid clones associated with P. formosa. Triploid females have erythrocytes that are significantly larger than those from diploid specimens and also show a roughly 50% elevation in the average DNA content of their somatic nuclei. Similar analyses of two functionally incompetent males of P. formosa, of a number of bisexual F1 and F2 hybrid offpsring from P. latipinna x P. mexicana, and of females from several other poeciliid species consistently show only diploid DNA levels and somatic chromosome complements where 22N=46. Demonstration of cytogenetic criteria by which females from triploid clones may be clearly distinguished from sympatric diploid specimens of P. formosa or P. mexicana leaves unresolved, for the present, problems of an appropriate systematic designation for natural populations of triploid gynogenetic fishes. The role of sympatric speciation in the evolution of poeciliid genomes is discussed in terms of alternative mechanisms to account for the persistence in nature of a vertebrate triploid of hybrid origin.
TL;DR: A comparison between the position of heterochromatic, late replicating and fluorescing segments in the mitotic chromosomes shows differences which demonstrate, for the first time, the chemical, morphological and genetical diversity of these three types of segments.
Abstract: Mitotic and salivary gland chromosomes of D. melanogaster show striking fluorescent patterns when stained with Quinacrine. In the salivary gland chromosomes there are up to five strongly fluorescing bands located on the fourth chromosome and at the proximal end of the X chromosome.—In mitotic cells the Y chromosome shows four fluorescent segments and other fluorescent regions are found proximally on the third pair and on the X chromosome. It is, therefore, possible to distinguish male and female interphase cells by their patterns of fluorescence.—A comparison between the position of heterochromatic, late replicating and fluorescing segments in the mitotic chromosomes, shows differences which demonstrate, for the first time, the chemical, morphological and genetical diversity of these three types of segments.
TL;DR: Locusta migratoria has only 70% of the germ line DNA value of the related species Schistocerca gregaria in spite of a uniform karyotype and the peaks in the distributions do not conform with members of a doubling series.
Abstract: Locusta migratoria has only 70% of the germ line DNA value of the related species Schistocerca gregaria in spite of a uniform karyotype. This difference is maintained in the nuclei of the testis wall, ovariole tip, mid-gut diverticulum, Malpighian tubule and fat. The distribution of nuclear DNA contents is tissue specific but the peaks in the distributions do not conform with members of a doubling series. It is suggested that both phenomena may be connected with the mechanism of tissue differentiation in insects, the latter by differential replication of those chromosome regions which are active in particular tissues.
TL;DR: The results strongly suggest that variation in chromosome size indicates a corresponding change in the rate of cell metabolism and may well reflect change in genetic activity.
Abstract: The natural variation in chromosome size in root-tip and shoot apex meristems of Vicia faba has been studied. Chromosomes in main root-tips of one week old plants are 2–3 times larger than those in small lateral root-tips of 3 week old plants. While the nuclear DNA content remains constant, the nuclear RNA and nuclear histone contents show a positive linear correlation with chromosome volume. The DNA: histone ratio varies and is lowest in cells with large chromosomes. Nuclear volume and chromosome volume are not linearly related and changes in nuclear density therefore seem likely. A positive linear relationship between chromosome volume and mitotic index in colchicined squashes is demonstrated. The results strongly suggest that variation in chromosome size indicates a corresponding change in the rate of cell metabolism and may well reflect change in genetic activity.
TL;DR: Heterochromatic chromosome regions are genetically inactive irrespective of their state of condensation in interphase, indicating that the genetic inactivity of heterochromatin is therefore not necessarily connected with heteropycnosis.
Abstract: In M. agrestis the large heterochromatic sex chromosomes may form heteropycnotic structures of varying size and degree of condensation in interphase nuclei of different tissues. In certain cell types (kidney epithelial cells in vitro, brain cells) the whole sex chromosomes of both sexes form large heteropycnotic chromocenters in interphase. Autoradiographs after incubation with H3-uridine show that in such cell nuclei the chromocenters are always free of label, indicating a transcription inactivity of the heterochromatic sex chromosomes. In other cell types (fibroblasts in vitro from female animals) only a small part of one of the two X-chromosomes is heteropycnotic in interphase, forming a “sex chromatin” like body. But also in such cells two areas, corresponding in size to the large chromocenters of the other cell types, are free of label. One of these two label free areas is consistently found in close proximity to the sex chromatin body. In cell nuclei without any heteropycnotic structures (some of the female and all male fibroblasts) two label-free areas can similarly be observed. — These findings indicate that heterochromatic chromosome regions are genetically inactive irrespective of their state of condensation in interphase. The genetic inactivity of heterochromatin is therefore not necessarily connected with heteropycnosis.
TL;DR: The transmission of complex chromosome rearrangements and fragments for 3 generations of outcrossing correlates with the persistence of sterility in this species possessing holokinetic chromosomes.
Abstract: AdultOncopeltus fasciatus males were irradiated with 9000 R of X-rays, and crossed to untreated females. Fertility was reduced to 4.1%. F1 males and F2 and F3 males and females were outcrossed to untreated partners. All F1 males were partially or totally sterile and a significant number of F2 and F3 males and females had reduced fertility. The fertility of each generation was higher than the preceding one, even though the progeny studied in the 3rd generation were selected mostly from low-fertility lines. Cytogenetic studies showed that complex chromosome rearrangements and fragments were transmitted to each generation and were severe enough to account for reduced fertility. — The transmission of complex chromosome rearrangements and fragments for 3 generations of outcrossing correlates with the persistence of sterility in this species possessing holokinetic chromosomes. — Over half the inviable embryos derived from irradiated sperm from P1 males died in the early stages of development. The inviable embryos produced in later generations died in much later stages of development. — A stable rearrangement of a Y-chromosome fragment translocated to an autosome was isolated from a single F1 male. This rearrangement was transmitted to all F2 and F3 sons. Fertility of the males of this line was reduced to about 75–80%.
TL;DR: It is proposed that interstitially located supernumerary segments may prove to be more common than has previously been accepted and that the rod chromosomes of many Acridids may well be telocentric as in the case under study.
Abstract: Three species of the genus Stethophyma carry supernumerary heterochromatic segments. The European species, S. grossa, has segments located close to the centromere on the S11 chromosome pair, while the North American species, S. lineatum and S. gracile, have both interstitial and terminal segments on the S10 and S11 chromosomes. The latter species show a high degree of segment variation between individuals and the interstitial segments also show variation in size. The presence of segments on the S10 and S11 chromosomes, whether homozygous or heterozygous, modifies the pattern of chiasma distribution in these chromosomes when compared with that found in the basic homozygotes. When interstitial, they also lead to a high frequency of ring bivalents.Two points suggest that interstitially located supernumerary segments may prove to be more common than has previously been accepted. Firstly, combined equational and reductional segregation in unequal bivalents is only otherwise explicable in terms of chiasma formation in a short arm. Secondly the rod chromosomes of many Acridids may well be telocentric as in the case under study.It is proposed that these segments have arisen through a process of duplication with no evidence of interchromosomal movement.
TL;DR: The microchromosomes of Japanese quail fibroblasts are shown to be heterochromatic and nucleolus-organizing and autoradiographic studies indicate that although some DNA replication takes place early, the time of intense replication is in the late S period after most replication in the macrochromosome has ceased.
Abstract: The microchromosomes of Japanese quail fibroblasts are shown to be heterochromatic and nucleolus-organizing. Autoradiographic studies indicate that although some DNA replication takes place early, the time of intense replication is in the late S period after most replication in the macrochromosomes has ceased. Analytical centrifugation of quail DNA demonstrated a main band with a buoyant density of 1.701 g/cm3 and a satellite constituting about 5% of the DNA with a buoyant density of 1.715. The G-C content of the main and satellite band was 42 and 55 percent respecively by both buoyant density and DNA Tm. The satellite band renatured much more rapidly than main band DNA indicating it was composed of highly repetitive sequences. When purified satellite DNA was centrifuged at pH 13 it separated into three portions, a major central band constituting 72% of the satellite DNA, and two smaller bands, one heavier and one lighter than the central band, each constituting 14% of the satellite DNA. This indicated that in a portion of the satellite DNA the bases were non-randomly distributed in the half-DNA helices.
TL;DR: The pattern of chiasma distribution along each of the five A bivalents was related to the DNA labelling pattern of mitotic chromosomes, and Regions that showed heavy labelling at the end of the DNA synthetic phase had fewer chiasmata than lightly labelled regions.
Abstract: The presence of the partly heterochromatic supernumerary chromosomes in pollen mother cells of Puschkinia libanotica raises the chiasma frequency in the A chromosome bivalents. The pattern of chiasma distribution along each of the five A bivalents was related to the DNA labelling pattern of mitotic chromosomes. Regions that showed heavy labelling at the end of the DNA synthetic phase had fewer chiasmata than lightly labelled regions. As this relation is the opposite to that found by Rees and Evans in another species we regard any correlation between labelling pattern and chiasma distribution as fortuitous.
TL;DR: The significance of the 8-nucleate condition in Ascaphus oocytes is discussed, and the amount of nucleolar DNA synthesized at pachytene and ofucleolar material present in germinal vesicles is compared with corresponding situations in other amphibians.
Abstract: In the last 3 oogonial mitoses in Ascaphus truei all daughter nuclei remain in the same cell. The oocyte is 8-nucleate at the start of meiotic prophase and remains so until late in oogenesis when 7 of the nuclei disappear. All 8 nuclei in a single oocyte resemble one another with respect to size and chromatin distribution at all stages of meiotic prophase. Much of the Feulgen-positive material in pachytene nuclei is concentrated into one region of the nucleus. — All of the 8 germinal vesicles of yolky oocytes have a full set of lampbrush diplotene bivalents. Germinal vesicles from oocytes of up to 0.8 mm diameter have less than 100 nucleoli, some of which are multiple nucleoli in the sense that they have more than one core region. Each of the 8 nuclei in oocytes from one animal had about the same volume of nucleolar material. — Two values have been obtained for the amount of DNA in a diploid nucleus from Ascaphus. A biochemical estimate utilizing erythrocyte nuclei and the diphenylamine reaction yielded a value of 7.1 pg per nucleus. Microphotometry of erythrocyte nuclei stained with Feulgen's reagent gave a value of 8.2 pg per nucleus. — Microphotometric measurements of Feulgen-stained nuclei at various stages of meiotic prophase up to diplotene indicate that each nucleus synthesizes up to 5 pg of extrachromosomal DNA during and immediately after pachytene. This DNA is considered to be nucleolar. Autoradiography of nuclei from oocytes which had been incubated for 6h in 3H thymidine showed silver grains over pachytene and early diplotene nuclei only. In pachytene nuclei the silver grains overlaid that part of the nucleus where Feulgen-positive material was most concentrated. Most of the chromosomal material was unlabelled. — The significance of the 8-nucleate condition in Ascaphus oocytes is discussed, and the amount of nucleolar DNA synthesized at pachytene and of nucleolar material present in germinal vesicles is compared with corresponding situations in other amphibians.
TL;DR: Two conflicting results can be reconciled by assuming that the same basic event, perhaps “stickiness” of the B9 chromosome, produces nondisjunction at the second pollen mitosis and isochromosome formation in the developing sporophyte.
Abstract: Bianchi et al. (1961) found that sectored losses of B-translocation chromosomes occur at a significant rate during early development of the endosperm and sporophyte. The losses were attributed to nondisjunction of the chromomosome, since B type chromosomes are known to undergo nondisjunction at the second pollen mitosis. Sector formation was further analyzed in the present paper, using the translocation, TB-9b. It was found that losses of the B9 chromosome during early endosperm mitoses occur only if the 9B chromosome is present. In addition, sectors are produced in the sporophyte only if the 9B and B9 chromosomes are inherited from the male parent. Both of these findings suggest that nondisjunction is indeed responsible for the B9 losses (see text). However, cytological observation of sectored plants demonstrates that isochromosome formation, rather than nondisjunction, produces most B9 losses in the sporophyte. The conflicting results can be reconciled by assuming that the same basic event, perhaps “stickiness” of the B9 chromosome, produces nondisjunction at the second pollen mitosis and isochromosome formation in the developing sporophyte. Observation of the isochromosome in pachytene reveals that a heterochromatic region corresponding to the short arm of the normal B9 is missing. The normal B9 chromosome is, therefore, an acrocentric chromosome.
TL;DR: The lampbrush chromosomes of Triturus vulgaris meridionalis were isolated from the germinal vesicle of medium and large-sized oocytes and studied with phase-contrast microscope to construct maps constructed on the basis of the lengths and major morphological features of the chromosomes.
Abstract: The lampbrush chromosomes of Triturus vulgaris meridionalis were isolated from the germinal vesicle of medium and large-sized oocytes and studied with phase-contrast microscope. The maps were constructed on the basis of the lengths and major morphological features of the chromosomes. The length of each map is equal to the mean of the relative lengths of the corresponding chromosome from different oocytes (the relative length of each chromosome is represented by the ratio between its absolute length and that of chromosome XII from the same complement, conventionally considered as 100 units long). The maps arranged in decreasing length order, were oriented according to the most frequent position of chiasmata, as centromeres were not always evident. — Chromosomes VI and XI bear a sphere in subterminal position. Landmarks typical for T. vulgaris meridionalis are the loops inserted on chromosomes VIII (47 units), X (23 units), XI (34 units) and XII (34 units) frequently presenting themselves under the form of double loop bridges of considerable extension. On chromosomes I (4 units), VI (13 units), X (4 units) and XI (36 units) giant bodies were found that are sometimes comparable to dense-matrix loops. Chromosome XI includes a nucleolus-organizing region, sometimes identifiable by the presence of an inserted nucleolus. Normal and granular loops (much extended at times), axial granules, globules, and loopless bars supplement the morphology of the lampbrush chromosomes of this species.
TL;DR: In certain stages of oocyte development, there is a striking correspondence in the number of bundles of the E chromosomes with the haploid number of the S chromosomes, which could be a hint to polyploidy of the supernumerary chromosomes.
Abstract: Autoradiographic and cytological investigations were performed to elucidate the role of supernumerary chromosomes (E chromosomes) in the oogenesis of Wachtliella persicariae. In contrast to the compact S chromosomes, these extra chromosomes are despiralized during the entire oogenesis (Fig. 1) and synthesize RNA (Fig. 10c). As no nucleoli could be found in the oocyte nucleus, the E chromosomes are thought to produce messenger RNA. — The S chromosomes are inactive in the first period of oocyte growth and surrounded by concentric lamellate bodies (Fig. 4). After degeneration of the nurse chamber, they also despiralize and synthesize RNA. — In certain stages of oocyte development, there is a striking correspondence in the number of bundles of the E chromosomes with the haploid number of the S chromosomes (Fig. 5). These findings could be a hint to polyploidy of the supernumerary chromosomes.