Showing papers in "Chromosoma in 1974"
TL;DR: Chinese hamster ovary cells grown for two rounds of DNA replication in the presence of BrdUrd contain sister chromatids that fluoresce differentially when stained with Hoechst 33258, and the staining patterns obtained in endoreduplicated cells clearly confirm that the polynucleotide strands of the DNA segregate into sister Chromatids as though the newly synthesized strands were laid on the outside of the replicating double helix.
Abstract: Chinese hamster ovary cells grown for two rounds of DNA replication in the presence of BrdUrd contain sister chromatids that fluoresce differentially when stained with Hoechst 33258. If such fluorescent treatments are followed by incubation in 2 X SSC or water at 62° C and staining in 3% Giemsa, the chromosomes now contain one dark (unifilarly substituted) chromatid and one light (bifilarly substituted) chromatid, i.e. are “harlequinized”. These preparations do not fade and can be studied without resorting to fluorescence microscopy. Sister chromatid exchanges (SCE's) are seen with great clarity and resolution; and all the chromosomes in a cell can be scored, which is contrary to the usual experience with autoradiography. It was found that a) the yield of SCE's is dependent upon the concentration of BrdUrd in which the cells are grown and that the maximum number of SCE's that can occur spontaneously is 0.15 per chromosome per division cycle, b) the yield of SCE's doubles if the cells are exposed to visible light that can cause the photolysis of BrdUrd-containing DNA, and c) chromosomes that appear isolabelled in autoradiographic preparations come from observable multiple exchanges and are not the result of the segregation of DNA from a binemic chromosome. Furthermore, the staining patterns obtained in endoreduplicated cells clearly confirm that the polynucleotide strands of the DNA segregate into sister chromatids as though the newly synthesized strands were laid on the outside of the replicating double helix.
565 citations
TL;DR: Chromatids singly and doubly substituted with BrdU acquire differential Giemsa stain affinities after treatment at 88° C for 10 minutes in 1.0 M Na phosphate buffer.
Abstract: Sister chromatid exchanges are sharply demarcated in Giemsa stained metaphase preparations of Chinese hamster ovary cells and human peripheral leukocytes. Chromatids singly and doubly substituted with BrdU acquire differential Giemsa stain affinities after treatment at 88° C for 10 minutes in 1.0 M Na phosphate buffer (pH 8.0).
330 citations
TL;DR: Ciliated protozoa are characterized by generative micronuclei and vegetative polyploid macron nuclei and their kinetic complexity can be determined by comparison with the kinetic complexity of E. coli DNA.
Abstract: Ciliated protozoa are characterized by generative micronuclei and vegetative polyploid macronuclei. Micronuclei of Stylonychia mytilus contain 1 600 times as much DNA per haploid genome as E. coli. Most of this DNA is shown to be repetitive. The development of the macronucleus involves, as demonstrated by cytology, only 1/3 of the chromosomes which in a first replication phase are polytenized in probably 5 replication steps and appear as giant chromosomes. At this developmental stage considerable amounts of repetitive DNA are still present in the chromosomes. During the subsequent disintegration phase more than 90% of the DNA are eliminated from the macronucleus anlage. The remainder is further replicated five times and composes the final macronucleus. Since this DNA reassociates with a reaction rate almost identical to an ideal second order reaction its kinetic complexity can be determined by comparison with the kinetic complexity of E. coli DNA. Macronuclear DNA reassociates with a kinetic complexity of 26 times the kinetic complexity of E. coli DNA (corrected for GC content) which indicates that macronuclear DNA sequences exist at a ploidy level of 4 096 C. We assume that macronuclear DNA may be present only once per haploid genome. In this case it represents only 1.6% of the DNA in micronuclei or 10% of the DNA in the giant chromosome stage.
277 citations
TL;DR: It was concluded that the probability of a chromosome being involved in the formation of a common nucleolus is not a simple function of its rDNA content and other possible factors are considered.
Abstract: 3H-rRNA obtained from Xenopus laevis tissue cultured cells, or a 3H-cRNA made from Xenopus ribosomal DNA, was used for heterologous in situ hybridisation with human lymphocyte metaphase chromosomes. Prior to hybridisation, chromosome spreads were stained with Quinacrine and selected cells showing good Q-banding photographed; the same cells were then rephotographed after autoradiography and pairs of photographs for each cell were used to make dual karyotypes. The chromosomes within each karyotype were divided into equal sized segments (approx. 0.7 μ), with a fixed number of segments for each chromosome type. The distribution of silver grains between segments showed that the 3H-RNAs hybridised specifically to the nucleolar organising regions of the D and G group chromosomes with no other sites of localised labelling in the complement. Control experiments showed no localisation, with insignificant labelling, when metaphase spreads were incubated in a mixture containing Xenopus3H-rRNA and competing cold human (HeLa) rRNA. Filter hybridisation experiments on isolated human DNA showed that the Xenopus derived 3H-RNAs hybridised to a fraction of human DNA which was on the heavy side of the main DNA peak and that these RNAs were competed out in the presence of excess cold human rRNA, confirming the specificity of the heterologous hybridisation. In situ hybridisation experiments were also carried out on cells from individuals with one chromosome pair showing heteromorphism for either a very long stalk (nucleolar constriction) subtending a satellite, or a large satellite. It was shown that the chromosome with the large stalk hybridised four times as much 3H-rRNA as its homologue, whereas differences in the sizes of the subtended satellites did not materially affect hybridisation levels indicating that rDNA is located in the stalks and not the satellites. The amount of 3H-rRNA hybridised differs between chromosomes and individuals; these differences are heritable and rDNA can be detected by in situ hybridisation in all three chromosomes number 21 in cells from Down's patients and in translocated chromosomes conta.ining a nucleolar constriction. Different D and G group chromosomes which hybridised equal amounts of 3H-rRNA participated in rosette associations at metaphase in a random fashion in some individuals and in a non-random fashion in others. In all individuals studied chromosomes with large amounts of rDNA were not found to be preferentially involved in association. It was therefore concluded that the probability of a chromosome being involved in the formation of a common nucleolus is not a simple function of its rDNA content and other possible factors are considered.
273 citations
TL;DR: The data obtained in this study with DNA polymers of defined structure or composition, as test model compounds, suggest that 33258 is a useful cytochemical reagent for generally identifying all types of AT-rich regions in chromosomes, including those which are not demonstrable with quinacrine.
Abstract: A new fluorescent probe of chromosomal DNA structure in situ, the bibenzimidazole derivative Hoechst 33258, shows enhanced fluorescence with both AT- and GC-rich DNA; however, enhancement by AT-rich DNA is greater than enhancement with GC-rich DNA. When this compound is used as a probe, it produces localized fluorescence which can be correlated with AT concentration in specific chromosome regions. By the use of 33258, Hilwig and Gropp (1972) were able to demonstrate the relatively AT-rich DNA present in centric regions of mouse chromosomes; these regions do not fluoresce brightly when treated with quinacrine because of the presence of guanine residues which are spaced with high periodicity and which therefore efficiently quench quinacrine fluorescence. The data obtained in this study with DNA polymers of defined structure or composition, as test model compounds, suggest that 33258 is a useful cytochemical reagent for generally identifying all types of AT-rich regions in chromosomes, including those which are not demonstrable with quinacrine.
231 citations
TL;DR: A major role had been played by centric fission as well as fusion, translocation, and pericentric inversion in birds to elucidate mechanisms involved in certain structural changes of macrochromosomes observed in birds.
Abstract: Karyotypes were compared in 48 species, including 6 subspecies, of birds from 12 orders: Casuariiformes, Rheiformes, Sphenisciformes, Pelecaniformes, Ciconiiformes, Anseriformes, Phoenicopteriformes, Gruiformes, Galliformes, Columbiformes, Falconiformes and Strigiformes. — With the exception of the family Accipitridae, all the species studied are characterized by typical bird karyotypes with several pairs of macrochromosomes and a number of microchromosomes, though the boundary between the two is not necessarily sharp. The comparative study of complements revealed that a karyotype with 3 morphologically distinct pairs of chromosomes is frequently encountered in all orders except the Strigiformes. Those 3 pairs, submetacentric nos. 1 and 2, and a subtelocentric or telocentric no. 3, are not only morphologically alike but also have conspicuous homology revealed by the G-banding patterns. Furthermore, G-banding analysis provided evidence for the derivation of the owl karyotype from a typical bird karyotype.—The above cytogenetic features led to the assumption that the 3 pairs of marker chromosomes had been incorporated into an ancestral bird karyotype. It seems probable that those chromosomes have been transmitted without much structural changes from a common ancestor of birds and turtles, since the presence of the same marker chromosomes in the fresh water turtle Geoclemys reevesii is ascertained by G-banding patterns. — A profile of a primitive bird karyotype emerged through the present findings. Hence, it has become possible to elucidate mechanisms involved in certain structural changes of macrochromosomes observed in birds. It was concluded that a major role had been played by centric fission as well as fusion, translocation, and pericentric inversion.
200 citations
TL;DR: Findings place severe constraint on possible models concerning the structure of the Tetrahymena macronucleus, and are very different from the situation observed in Stylonychia where it has been suggested that only a small percentage of the sequences in micronuclei are present in significant amounts in macron nuclei.
Abstract: Macro- and micronuclei were isolated from Tetrahymena pyriformis (Syngen 1, strain WH-6) and their DNAs compared by isopycnic centrifugation in neutral and alkaline CsCl, by analysis of thermal denaturation properties and by molecular hybridization. Unlike the situation observed in Stylonychia the buoyant densities and thermal denaturation patterns of Tetrahymena macro- and micronuclear DNAs were virtually identical—the only observable differences bordering on the limits of resolution of these techniques. DNA was isolated from the two nuclei which had been labelled with different radioactive isotopes (i.e.
14C-thymidine and 3H-thymidine), and the renaturation kinetics of mixtures of macro- and micronuclear DNA were examined using a single-strand specific deoxyribonuclease (S1). Renaturation kinetics obtained using varying ratios of macro- and micronuclear DNA suggested that 80–90% of the sequences present in micronuclei were present in similar amounts in macronuclei. However, careful analyses of the renaturation kinetics indicate that approximately 10–20% of the sequences found in micronuclei are probably absent in macronuclei, and that most of these sequences are probably moderately repetitive (100 copies per genome or less). These findings place severe constraint on possible models concerning the structure of the Tetrahymena macronucleus, and are very different from the situation observed in Stylonychia where it has been suggested that only a small percentage of the sequences in micronuclei are present in significant amounts in macronuclei. Nonetheless, these results along with those in Stylonychia can be taken as an indication that the loss or under-replication of some DNA sequences accompanies macronuclear differentiation in ciliates.
190 citations
TL;DR: The New Mexican species was exceptional in showing little homology with other species with respect to either repetitive or slowly reassociating sequences, but higher levels of homology were observed in the case of repetitive sequences.
Abstract: Chromosomes and DNA sequence homologies have been studied in 15 species of North American salamander belonging to the genus Plethodon. These include 4 Eastern small species, 5 Eastern large species, 5 Western, and 1 New Mexican species. All species have 14 metacentric or sub-metacentric chromosomes. Their karyotypes are closely similar, but their C values range from 18–69 pg. DNA:DNA molecular hybridization studies showed that salamanders belonging to the same species group had between 60 and 90% of the observed repetitive DNA sequences in common, different groups of Eastern species had between 40 and 60% in common, and Eastern and Western groups had less than 10% in common. The slowly reassociating DNA sequences were also diverse among species, but higher levels of homology were observed than in the case of repetitive sequences. The New Mexican species was exceptional in showing little homology with other species with respect to either repetitive or slowly reassociating sequences.
147 citations
TL;DR: Electron microscopic examinations revealed that many chromosomes are connected by submicroscopic chromatin strands of various widths, which is interpreted as entanglement of chromatin fibers between unrelated chromosomes, probably caused by abnormal condensation behaviors prior to mitosis.
Abstract: When two types of mammalian cells were treated with ethidium bromide for several hours, the mitotic figures showed no chromatid breaks or exchanges but a high incidence of sticky chromosomes. Electron microscopic examinations revealed that many chromosomes are connected by submicroscopic chromatin strands of various widths. Chromosome stickiness, therefore, is interpreted as entanglement of chromatin fibers between unrelated chromosomes, probably caused by abnormal condensation behaviors prior to mitosis. Presumably, chromatin breaks would occur when sticky chromosomes separate during anaphase. Such microscopically undetectable breaks expressed as various kinds of chromosomal aberrations in the next mitosis when the damaged cells were permitted to recover in the absence of ethidium bromide.
141 citations
TL;DR: The nature of the centromere and the orientation in meiosis of Silkworm chromosomes were investigated using the trivalent of the F1 hybrid between the wild and domestic silkworm and X-ray-induced aberrant chromosomes as well as normal silkworm chromosomes.
Abstract: The nature of the centromere and the orientation in meiosis of silkworm chromosomes were investigated using the trivalent of the F1 hybrid between the wild and domestic silkworm and X-ray-induced aberrant chromosomes as well as normal silkworm chromosomes. The results of the experiments were as follows: (1) Pro-metaphase chromosomes showed no distinct primary constriction even after treatment with hypotonic solution, (2) sister chromatids separated in parallel along the entire length of the chromosome at mitotic anaphase, (3) chiasmata underwent complete terminalization during diakinesis and thus chromosome dyads were always connected end-to-end by a terminal chiasma at metaphase I, (4) radiation-induced aberrant chromosomes were stably transmitted throughout a number of cell generations, and (5) although the homomorphic bivalents generally orientated axially at metaphase I and equatorially at metaphase II, this normal sequence tended to be inverted or modified in the X-ray-induced aberrant chromosomes and in the trivalent of the F1 hybrid silkworms. These observations may be best interpreted by assuming the holocentric nature of silkworm chromosomes.
134 citations
TL;DR: In this article, it was shown that the final plane of division is not determined by the orientation of the spindle at metaphase, but instead is established during late anaphase-telophase as a result of directed reorientation movements of spindle-phragmoplast and associated daughter nuclei.
Abstract: Division of the guard mother cell (GMC) in Allium cotyledons has been examined in epidermal slices viewed with Nomarski optics and electron microscopy Special attention has been directed towards elucidating the process by which the dividing cell determines its plane of division In normal development, the cell plate formed during GMC division ultimately lies along the longitudinal axis of the cotyledon, in contrast to the transverse planes formed in other epidermal divisions Our observations reveal that the final plane of division is not determined by the orientation of the spindle at metaphase but instead is established during late anaphase-telophase as a result of directed reorientation movements of the spindle-phragmoplast and associated daughter nuclei The metaphase plate may lie at an oblique angle, even as great as 90°, from the final plane of the plate Thus, daughter chromosomes separate into opposite corners of the cell During late anaphase-telophase, movement of the spindle is activated; the daughter nuclei move along the sides of the cell while the interzone rotates Movement continues until daughter nuclei reach positions opposite each other along the sides of the cell and the midzone or cell plate is positioned in the longitudinal orientation Movement requires 15–20 minutes for completion, is highly directional, and does not overshoot the correct alignment Following movement cytokinesis proceeds to completion forming two young guard cells Possible mechanisms for reorientation are discussed, including one that suggests that interzone microtubules may interact with a cortical site on the plasmalemma adjacent to the end and paradermal walls Such a site may be related to and governed by the same properties which controlled the prior formation of the preprophase band of microtubules in these cells
TL;DR: Chromatid interchange between somatic chromosomes, a phenomenon occasionally observed in normal lymphocytes in culture, occurs with a greatly increased frequency in Bloom's syndrome lymphocytes.
Abstract: Chromatid interchange between somatic chromosomes, a phenomenon occasionally observed in normal lymphocytes in culture, occurs with a greatly increased frequency in Bloom's syndrome lymphocytes. Highly characteristic interchanges occur at apparently homologous sites on homologous chromosomes and affect certain regions preferentially.
TL;DR: The higher the chiasma frequency of a population the lower the phenotypic and genetic variance for characters under polygenic control, such as flowering time, and the less effective also is the response to selection for such characters.
Abstract: There are significant differences in mean pollen mother cell chiasma frequencies between populations within Lolium perenne, L. multiflorum and Festuca pratensis. The differences are genotypically controlled. With low chiasma frequencies the chiasmata are distally located. With increasing chiasma frequency the frequency of chiasmata in interstitial segments increases. Shorter lived populations have higher chiasma frequencies than the more perennial. — The higher the chiasma frequency of a population the lower the phenotypic and genetic variance for characters under polygenic control, such as flowering time, and the less effective also is the response to selection for such characters. These observations are interpreted on the premise that high chiasma frequencies are instrumental in the breaking up of supergene sequences in interstitial chromosome segments.
TL;DR: The behavior of heterochromatin during premature chromosome condensation (PCC) was studied in a cell line of Microtus agrestis after fusion with mitotic HeLa cells.
Abstract: The behaviour of heterochromatin during premature chromosome condensation (PCC) was studied in a cell line of Microtus agrestis after fusion with mitotic HeLa cells. In the G1- and G2-PCC, the heterochromatic nature of the X-chromosomes was detectable by their intense staining. The pulverized appearance of the S-phase PCC was correlated with incorporation of 3H TdR into the DNA. Three types of S-PCC were observed. PCC with a pulverized appearance of: (a) only the autosomes (early S); (b) autosomes and X-chromosomes (mid S); and (c) only the X-chromosomes (late S). The behaviour of heterochromatin during replication, as observed by the PCC method, was no different from that of euchromatin. The data on the sequence of chromosome replication indicate that the centromeric regions of the X-chromosomes were the last segments to replicate. The completion of DNA synthesis in the X-chromosomes appears to be followed by progressive chromosome condensation during G2 even before the actual initiation of prophase.
TL;DR: Banding patterns were revealed in the karyotypes of six species of Anemone and in Hepatica nobilis using a Giemsa staining technique and there was considerable inter-specific variation both regarding the amount and distribution of bands.
Abstract: Banding patterns were revealed in the karyotypes of six species of Anemone and in Hepatica nobilis using a Giemsa staining technique. — There was considerable inter-specific variation both regarding the amount and distribution of bands. Small but significant intra-specific differences in banding patterns were also found. The results are discussed both as they relate to the use of Giemsa banding in karyotype analysis and to understanding the nature of the banding phenomenon itself.
TL;DR: In situ hybridization of I125-labelled ribosomal RNA to mouse chromosomes was used to determine the location of the rDNA loci and demonstrated the presence of rDNA sites on chromosomes 15, 18 and 19.
Abstract: In situ hybridization of I125-labelled ribosomal RNA to mouse chromosomes was used to determine the location of the rDNA loci. The results demonstrate the presence of rDNA sites on chromosomes 15, 18 and 19.
TL;DR: The number of active ribosomal eistrons found in some X-Y translocation stocks and in XO males deviates considerably from that expected on the basis of DNA/RNA hybridization data, and it is concluded that a mechanism adjusting the number of Ribosomal cistrons may be operating in these cases.
Abstract: Transcribing ribosomal RNA genes in primary spermatocyte nucleoli of Drosophila hydei have been visualized by electron microscopy using a microspreading technique. The length of the transcribing unit is in agreement with the length of the ribosomal RNA precursor as determined by acrylamide gel electrophoresis (2.6×106 daltons). The length of the non-transcribed spacer is approximately 1.0×106 daltons. The maximum number of active cistrons in wild type (XY) males only approaches one half the estimated number of ribosomal cistrons of the replicated diploid genome (∼300) of D. hydei and is found to vary between 120 and 320 cistrons in different developmental stages of spermatocytes. There is also some variation between different males. In a few cases a variation in the transcriptional activity of different cistrons has been observed. The synthesis of ribosomal RNA therefore seems to be regulated primarily by the activation or inaetivation of varying numbers of ribosomal cistrons. Groups of adjacent cistrons seem to be under coordinated control. Inhibition of RNA synthesis by actinomycin, in contrast, follows a random pattern. The frequent observation of a bipartite nucleolus indicates that the nucleolus organizer regions of the two sex chromosomes are both active in transcription. The number of active ribosomal eistrons found in some X-Y translocation stocks and in XO males deviates considerably from that expected on the basis of DNA/RNA hybridization data. We conclude that, in agreement with the observations of other authors, a mechanism adjusting the number of ribosomal cistrons may be operating in these cases.
TL;DR: Results suggest that determination of the correct plane of division is an energy requiring process and interzone microtubules appear essential for spindle reorientation either by acting as cytoskeletal agents or by providing the force necessary for movement.
Abstract: The correct positioning of the plane of the cell plate of the dividing guard mother cell (GMC) of Allium is controlled by reorientation movements of the spindle-phragmoplast structure during anaphase-telophase, as described in a previous publication (Palevitz and Hepler, 1974). In an attempt to clarify the mechanism of movement a series of experiments involving the application of different drugs has been performed. The metabolic inhibitors, azide, 2–4 DNP and cyanide reversibly block reorientation. The antimicrotubule agents, colchicine, vinblastine sulfate and isopropyl-N-phenylcarbamate (IPC) prevent reorientation and cause shrinkage of the interzone. They also produce aberrant and malaligned cell plates. Caffeine has no effect on reorientation although it inhibits cell plate formation. Cytochalasin B (CB) produces variable effects; frequently, but not always, it blocks reorientation and induces misshapened cell plates. These results suggest that determination of the correct plane of division is an energy requiring process. In addition interzone microtubules appear essential for spindle reorientation either by acting as cytoskeletal agents or by providing the force necessary for movement.
TL;DR: X chromatin in man condenses around a center which is situated on Xq at a short distance from the centromere, so that chromosomes lacking the center would form no Barr body and therefore presumably would not be inactivated, thus leaving the cell severely unbalanced.
Abstract: The following hypothesis is put forward: X chromatin in man condenses around a center which is situated on Xq at a short distance from the centromere. The hypothesis is based on, and explains, two classes of observations. (1) Abnormal X chromosomes that have the assumed center in duplicate form bipartite Barr bodies in part of the cells. The frequency of bipartite bodies and the distance between the two parts seem to be determined by the distance between the postulated centers. (2) A large number of variously abnormal X chromosomes have been described. Almost all of them possess the postulated center and it seems possible that the very few apparent exceptions represent misidentifications of chromosome Xq — as isochromosome i(Xp). According to the hypothesis, chromosomes lacking the center would form no Barr body and therefore presumably would not be inactivated, thus leaving the cell severely unbalanced. Furthermore, absence of the center might interfere with the viability of the chromosome itself.
TL;DR: The size and nucleotide sequence complexity of the Bombyx mori genome has been determined from the kinetics of reassociation of its DNA and compares favorably with the DNA content of haploid B. mori spermatids and mature sperm determined cytophotometrically by Rasch (1973).
Abstract: The size and nucleotide sequence complexity of the Bombyx mori genome has been determined from the kinetics of reassociation of its DNA. Nonrepeated DNA comprises 55% of the genome, and the remainder is divided equally between sequences repeated roughly 500 and 50000 times. Non-repeated sequence DNA virtually free of repeated sequences was prepared by partial reassociation and subsequent fractionation on hydroxyapatite. The nucleotide sequence complexity of this component was determined relative to DNA from B. subtilis and E. coli. After correction for the size of the repeated sequence fraction, the DNA content of the Bombyx mori genome was calculated to be 0.53±0.02×10−12 g. This value compares favorably with the DNA content of haploid B. mori spermatids and mature sperm determined cytophotometrically by Rasch (1973).
TL;DR: From the virtual absence of chiasmata in metaphase I stages of the haploids it is inferred that crossing over requires a more precise DNA alignment than is provided by synaptonemal complex formation alone.
Abstract: Normal synaptonemal complexes have been found in haploid barley meiotic prophase at stages equivalent to pachytene in diploids. Reconstructions of serially sectioned nuclei have shown that up to 60% of the haploid chromosomes may pair in either intra- or interchromosomal associations. The extent and nature of the synaptonemal complex formation suggest that the chromosome pairing is non-homologous. From the virtual absence of chiasmata in metaphase I stages of the haploids it is inferred that crossing over requires a more precise DNA alignment than is provided by synaptonemal complex formation alone.
TL;DR: It was observed that the chromosomes of the complement were capable of responsing to the treatment with analogs by the appearance of extended segments along their length, and the most regular and distinctive segmentation was observed in chromosomes having large late replicating regions, such as Nos. 4, 6, 9, 13, 16, X, and Y.
Abstract: The morphology of human metaphase chromosomes of peripheral blood lymphocytes taken from normal persons of both sexes and cultured at the final stages of the S-period in the presence of 5-bromodeoxyuridine (BUdR), or 5-bromodeoxycytidine (BCdR) was studied. It was observed that the chromosomes of the complement were capable of responsing to the treatment with analogs by the appearance of extended segments along their length. The pattern of segmentation was constant and specific for a given chromosome, serving as a basis for its identification, and appeared to be similar for both analogs. — Autoradiography of such chromosomes performed with 3H-thymidine (3H-TdR), 3H-deoxycytidine (3H-CdR), and 3H-BUdR showed that the extended chromosomal segments are late replicating. In accordance with this correlation, the most regular and distinctive segmentation was observed in chromosomes having large late replicating regions, such as Nos. 4, 6, 9, 13, 16, X, and Y. — A comparative analysis of the BUdR-induced differential spiralization pattern and banding pattern obtained with the G-staining technique was carried out. A good correspondence between the extended segments and Giemsa-positive bands was found. The data are discussed in relation to the mechanism of differential staining of metaphase chromosomes.
TL;DR: In hexaploid wheat and diploid rye, different varieties have different numbers of ribosomal RNA genes as indicated by rRNA/DNA hybridisation, but analyses of DNA isolated from substitution lines have indicated that none of the four organiser chromosomes possess an invariant number of riboRNA genes.
Abstract: In hexaploid wheat and diploid rye, different varieties have different numbers of ribosomal RNA genes as indicated by rRNA/DNA hybridisation. Wheat has four different chromosomes which carry nucleolar organisers. Analyses of DNA isolated from substitution lines in which each of these nucleolar organiser chromosomes of several varieties has been substituted one at a time into a common genetic background, have indicated that none of the four organiser chromosomes possess an invariant number of ribosomal RNA genes. The ribosomal RNA gene complement of the varieties investigated can be approximately accounted for by the sum of the ribosomal RNA genes on each of the four nucleolar organiser chromosomes.
TL;DR: The major concentrations of human satellite DNA I (1.688 g/ml) have been localised on human chromosome preparations by the technique of in situ hybridisation using radioactive complementary RNA synthesised in vitro.
Abstract: The major concentrations of human satellite DNA I (1688 g/ml) have been localised on human chromosome preparations by the technique of in situ hybridisation using radioactive complementary RNA synthesised in vitro Chromosomes were identified by prior study using quinacrine fluorescence microscopy The satellite DNA is concentrated, mainly in centromeric constitutive heterochromatin, on many chromosomes but is especially obvious in the fluorescent distal segment of the Y chromosome
TL;DR: These values compare favorably with estimates of genome size based upon analysis of the kinetics of reassociation of DNA isolated from B. mori and provide an independent basis for assessing the degree of polyploidy achieved by the giant nuclei in the posterior silk gland prior to its secretion of fibroin at the end of the fifth larval instar.
Abstract: To estimate the size of the haploid genome of the silkworm, Bombyx mori (Lepidoptera), amounts of Feulgen-DNA staining in individual nuclei of primary spermatocytes, spermatids, maturing sperm, and larval or pupal hemocytes were determined with an integrating microdensitometer and compared with the Feulgen-DNA levels found for chicken erythrocyte nuclei, or the sperm and erythrocyte nuclei of Xenopus laevis that were included with each Bombyx preparation as empirical reference standards of 2.5, 3.15, and 6.3×10−12 g DNA per cell, respectively. Under these conditions, the haploid male genome of B. mori was estimated as 0.52±0.01 (S.E.)×10−12 g DNA, corresponding to a molecular weight of roughly 3.1×1011 daltons. From similar measurements of Feulgen-stained hemocyte nuclei, approximately 1.0±0.05 (S.E.)×10−12 g DNA was estimated for the diploid or 2C male genome of Bombyx. These values compare favorably with estimates of genome size based upon analysis of the kinetics of reassociation of DNA isolated from B. mori and provide an independent basis for assessing the degree of polyploidy achieved by the giant nuclei in the posterior silk gland prior to its secretion of fibroin at the end of the fifth larval instar.
TL;DR: The fluorescence and circular dichroism of quinacrine complexed with nucleic acids and chromatin were measured to estimate the relative magnitudes of factors influencing the fluorescence banding patterns of chromosomes stained with quinACrine or qu inacrine mustard.
Abstract: The fluorescence and circular dichroism of quinacrine complexed with nucleic acids and chromatin were measured to estimate the relative magnitudes of factors influencing the fluorescence banding patterns of chromosomes stained with quinacrine or quinacrine mustard. DNA base composition can influence quinacrine fluorescence in at least two ways. The major effect, evident at low ratios of quinacrine to DNA, is a quenching of dye fluorescence, correlating with G-C composition. This may occur largely prior to relaxation of excited dye molecules. At higher dye/DNA saturations, which might exist in cytological chromosome preparations stained with high concentrations of quinacrine, energy transfer between dye molecules converts dyes bound near G-C base pairs into energy sinks. In contrast to its influence on quinacrine fluorescence, DNA base composition has very little effect on either quinacrine binding affinity or the circular dichroism of bound quinacrine molecules. The synthetic polynucleotides poly(dA-dT) and poly(dA)-poly(dT) have a similar effect on quinacrine fluorescence, but differ markedly in their affinity for quinacrine and in the circular dichroism changes associated with quinacrine binding. Quinacrine fluorescence intensity and lifetime are slightly less when bound to calf thymus chromatin than when bound to calf thymus DNA, and minor differences in circular dichroism between these complexes are observed. Chromosomal proteins probably affect the fluorescence of chromosomes stained with quinacrine, although this effect appears to be much less than that due to variations in DNA base composition. The fluorescence of cytological chromosome preparations may also be influenced by fixation effects and macroscopic variations in chromosome coiling.
TL;DR: The G-band patterns of mitotic metaphase chromosomes No. 1 and 2 of the Chinese hamster cells correlate closely to the chromomere patterns of the meiotic pachytene bivalents, interpreted to indicate that the regions of centromeric and intercalary heterochromatin, which are more tightly condensed or more tightly packaged during interphase, tend to remain so during meiosis and mitosis.
Abstract: The G-band patterns of mitotic metaphase chromosomes No. 1 and 2 of the Chinese hamster cells correlate closely to the chromomere patterns of the meiotic paehytene bivalents. This is interpreted to indicate that the regions of centromeric and intercalary heterochromatin, which are more tightly condensed or more tightly packaged during interphase, tend to remain so during meiosis and mitosis.
TL;DR: In further studies on DNA from larval diploid tissues, the following findings were made: 1) the Ybb-chromosome carries no rDNA; 2) flies carrying four nucleolus organizers do not tend to lose rDNA, even after eleven generations, and 3) theucleolus organizer on the wild type Y chromosome may have significantly less rDNA than does that on the corresponding X chromosome.
Abstract: The proportion of the Drosophila genome coding for ribosomal RNA was examined in DNA from both diploid and polytene tissues of Drosophila melanogaster by rRNA-DNA hybridization. Measurements were made on larvae with one, two, three and four nucleolus organizer regions per genome. In DNA from diploid tissues the percent rDNA (coding for 28S and 18S ribosomal DNA) was found to be in proportion to the number of nucleolus organizers present. The number of rRNA genes within a nucleolus organizer therefore does not vary in response to changes in the number of nucleolus organizers. On the other hand, in DNA from cells with polytene chromosomes the percent rDNA remained at a level of about 0.1% (two to six times lower than the diploid values), regardless of either the number of nucleolus organizers per genome or whether the nucleolus organizers were carried by the X or Y chromosomes. This independence of polytene rDNA content from the number of nucleolus organizers is presumably due to the autonomous polytenization of this region of the chromosome. When the rDNA content of DNA from whole flies is examined, both the rDNA additivity of the diploid cells and the rDNA independence of polytene cells will affect the results. This is a possible explanation for the relative rDNA increase known to occur in X0 flies, but probably not for the phenomenon of rDNA magnification. — In further studies on DNA from larval diploid tissues, the following findings were made: 1) the Ybb-chromosome carries no rDNA; 2) flies carrying four nucleolus organizers do not tend to lose rDNA, even after eleven generations, and 3) the nucleolus organizer on the wild type Y chromosome may have significantly less rDNA than does that on the corresponding X chromosome.
TL;DR: A Giemsa C-banding technique applied to the mosquito, Aedes aegypti, has revealed a distinctive banding pattern which is described as a reliable means of distinguishing between the morphologically similar X and Y chromosomes during all stages of mitosis and meiosis.
Abstract: A Giemsa C-banding technique applied to the mosquito, Aedes aegypti, has revealed a distinctive banding pattern which is described as a reliable means of distinguishing between the morphologically similar X and Y chromosomes during all stages of mitosis and meiosis. The essential difference is that the Y chromosome, unlike the X and the autosomes, is not C-banded in the centromere region. An intercalary band is also present in one arm of all X chromosomes and some Y chromosomes. The distribution of these cytological markers throughout meiosis indicates that the sex locus occurs somewhere within a pericentric region, the minimum extent of which includes both the intercalary band and the centromere.
TL;DR: Microsporocytes of Lilium that are exposed to colchicine as late as early zygotene show reduced chiasma frequencies and the presence of univalents at Division I, and chiasMA formation appears to be reduced by failures in synapsis.
Abstract: Microsporocytes of Lilium that are exposed to colchicine as late as early zygotene show reduced chiasma frequencies and the presence of univalents at Division I. These effects are preceded at pachytene by the appearance of pairing gaps (light microscopy) and by a relatively high ratio of uncomplexed lateral elements/synaptonemal complexes (EM). Chiasma formation thus appears to be reduced by failures in synapsis. Unlike the behavior of wheat, colchicine can disrupt chiasma formation in Lilium after cells have entered meiosis.