Showing papers on "Ploidy published in 1969"
TL;DR: Electron microscopy of dividing nuclei has revealed that mitosis is carried out within the intact nuclear envelope, and it is proposed that the chromosomes become attached to the central spindle at various points along its length.
Abstract: Mitosis in growing hyphae of haploid and diploid Aspergillus nidulans has been studied with the light microscope in Helly-fixed preparations. At the periphery of the nuleus a sharply defined granule is invariably found which has strong affinity for acid fuchsin. Mitosis begins with the duplication of this granule and the development inside the nucleus of a gradually lengthening fibre between the daughter granules. This fibre is also visibel in dividing nuclei of living hyphae examined by phase-contrast microscopy, when it appears as a grey bar traversing the non-nucleolar region. Division of the chromatin has been studied in preparations stained with aceto orcein, directly or after hydrolysis. It proceeds through four phases, beginning with the condensation of distinct chromosomes from the chromatin network of the resting nuclei. Later the chromosomes become arranged in two parallel rows of chromatinic masses in which individual chromosomes can no longer be distinguished. Division is completed by migration of the chromatin to the ends of each row, giving the appearance of a transverse break in the double bar. The chromatin accumulating at the ends of the double bar condenses to form the two daughter nuclei. The number of chromatinic elements appears to be the same in both haploid and diploid nuclei, although the individual elements are larger in the latter. Successive staining of the same dividing nucleus, first for the fibre (acid fuchsin) and then for the chromosomes (HCl-aceto orcein or HCl-Giemsa) has established that the fibre lies among the chromosomes, and that is elongation is closely related to the anaphase-telophase movements of the chromosomes. This suggests that the fibre is the equivalent of a mitotic spindle. That the fibre is connected with the chromosomes is further suggested by the observation that, in stained preparations, the fibre is considerably thicker in dividing diploid than in haploid nuclei. Electron microscopy of dividing nuclei has revealed that mitosis is carried out within the intact nuclear envelope. The mitotic spindle is composed of a bundle of fibrils which traverses the nucleus between two plaques of dense material associated with the envelope. In order to explain the configurations seen during the division of the chromatin it is proposed that the chromosomes become attached to the central spindle at various points along its length. With the elongation of the spindle the sister chromatids separate and pass, asynchronously, to opposite ends of the spindle along two preferred lines, thereby producing the characteristic double bar figure. The absence of a metaphase plate is thus accounted for by the scattered points of attachment of the chromosomes to the spindle and by their asynchronous division.
144 citations
TL;DR: Four forms of mole rats with diploid numbers of chromosomes of S2, 54, 58, and 60, respectively, were found in Israel and the vicinity and are tentatively considered as sibling species, almost completely isolated by cytogenetic and possibly ethological mechanisms.
Abstract: Four forms of mole rats with diploid numbers of chromosomes of S2, 54, 58, and 60, respectively, were found in Israel and the vicinity. The differences between the chromosome sets are due to whole-arm (Robertsonian) changes and pericentric inversions. The geographic distribution of the different forms is contiguous. Only a few hybrid individuals have been discovered. These chromosome forms are tentatively considered as sibling species, almost completely isolated by cytogenetic and possibly ethological mechanisms. The weak dispersal powers of mole rats may have-contributed to a rapid fixation of adaptive homozygous chromosomal changes.
125 citations
Journal Article•
97 citations
TL;DR: Somatic cell hybrids have been made between an established human cell line with a long culture history and established mouse fibroblast line and the number of human chromosomes is greater than in hybrids made from human diploid fibroblasts.
Abstract: Somatic cell hybrids have been made between an established human cell line with a long culture history and established mouse fibroblast line. When first analyzed, the hybrid cells contained nearly twice as many mouse chromosomes as the mouse parent line and a human chromosome complemnent of about half that of the human parent. There was further loss of human chromosomes on continued cultivation. This behavior resembles that of other human mouse hybrids and appears to be characteristic of the human-mouse combination. However, the number of human chromosomes is greater than in hybrids made from human diploid fibroblasts. Some clones contain more than a haptoid quantity of human DNA per cell and should synthesize a much greater number of human gene products.
93 citations
TL;DR: Ploidy-specific properties in morphological characteristic points are shown in plants restored from anther callus and tetraploid from ovary callus, although only diploid plants were restored from embryo and shoot nodule callus.
Abstract: Successful production of haploid, triploid and pentaploid as well as diploid was achieved in the plants restored from anther callus and tetraploid from ovary callus, although only diploid plants were restored from embryo and shoot nodule callus. A series of plants in polyploid, x, 2x, 3x, 4x, and 5x, showed the ploidy-specific properties in morphological characteristic points.
93 citations
TL;DR: The chromosome number of these cultures was determined, which could then be compared with those of the commercial hybrid to determine if a change had occurred in chromosome number, and this has implications in the use and interpretation of data from pathological, cytogenetical, biochemical, and physiological studies using cell cultures.
Abstract: A B S T R A C T Chromosome numbers of five Saccharum species hybrids and their cell suspension cultures were determined. The chromosome number was stable in four parental clones (2n = 122, 114, 114, and 112), but was variable in another (2n = 108-128). The cell suspension cultures have been maintained in a yeast extract-enriched nutrient medium for more than 6 years. These cultures were variable in chromosome number for all clones, with a partial aneuploid series at the haploid and/or polyploid level. Each clone had different chromosomal population modes after 6 years of culture. The loss of chromosomes over a period of time would have an effect on the genetic makeup of a cell population. This has implications in the use and interpretation of data from pathological, cytogenetical, biochemical, and physiological studies using cell cultures and is probably a partial explanation for the loss of totipotency in 6-year-old sugarcane tissue and suspension cultures. SUGARCANE CELL suspension cultures are being used at our experiment station in biochemical, physiological, cytogenetical, and pathological studies. The identification of suspension cultures with stable chromosome levels would be useful in the interpretation of certain phases of these studies. Suspension cultures of several commercial sugarcane hybrids have been maintained on the same medium, under the same conditions, for 6 years. The present study was undertaken to determine the chromosome number of these cultures, which could then be compared with those of the commercial hybrid to determine if a change had occurred in chromosome number.
78 citations
TL;DR: Electron micrographs of serial sections through a meiotic prophase nucleus of the mycetozoan Labyrinthula sp.
Abstract: Electron micrographs of serial sections through a meiotic prophase nucleus of the mycetozoan Labyrinthula sp. show that there are nine separate and distinct synaptinemal complexes. Since each complex represents a set of paired homologous chromosomes, it follows that the haploid chromosome number of this protist is nine.
73 citations
TL;DR: Two male diploid fibroblast strains, each carrying deficiency mutations at different X-linked loci (glucose-6-phosphate dehydrogenase and hypoxanthine-guanine- phosphoribosyltransferase) have been successfully hybridized, indicating that both X chromosomes are functionally active in the hybrid cells.
Abstract: Two male diploid fibroblast strains, each carrying deficiency mutations at different X-linked loci (glucose-6-phosphate dehydrogenase and hypoxanthine-guanine-phosphoribosyltransferase) have been successfully hybridized. The resulting mononucleated hybrid cells have been shown to synthesize both normal gene products, indicating that both X chromosomes are functionally active in the hybrid cells. We believe this is the first reported example of intergenic complementation in fused human diploid cells.
69 citations
TL;DR: Somatic segregation for three different autosomes was demonstrated in two strains of human diploid fibroblasts derived from subjects known to be heterozygous for chromosomal variants, suggesting a parasexual cycle with recombination of entire linkage groups could from the basis of a beginning formal genetic analysis in man.
Abstract: Somatic segregation for three different autosomes was demonstrated in two strains of human diploid fibroblasts derived from subjects known to be heterozygous for chromosomal variants. Recombinant diploid cells appeared within cultures of tetraploid clones isolted from mass cultures. Tetraploid cells regularly occur in mass cultures and within clones of diploid cells. Such a parasexual cycle (2n-->4n-->2n), with recombination of entire linkage groups, could from the basis of a beginning formal genetic analysis in man.
64 citations
TL;DR: Cytological examination revealed that all plants had 2n = 7 chromosomes and the vegetative characters of most of these haploids were intermediate between those of the two parental species whereas all haploids had the spike characters of H. vulgare.
Abstract: Ninety-seven hybrid seeds were obtained from seven crosses of Hordeum bulbosum (2x) × H. vulgare (2x), using embryo culture. Cytological examination revealed that all plants had 2n = 7 chromosomes. The vegetative characters of most of these haploids were intermediate between those of the two parental species whereas all haploids had the spike characters of H. vulgare. Possible origins from true nuclear gene hybridity followed by somatic reduction or by male parthenogenesis with differences in plasmagene activity are discussed.
TL;DR: A cytological and cytochemical examination of Sapro Legnia terrestris Cookson was undertaken to resolve the conflict of opinion regarding the life cycle of fungi in the Saprolegniaceae, i.e., whether meiosis is zygotic or gametic, and the evidence is completely consistent with gametic meiosis.
Abstract: A cytological and cytochemical examination of Saprolegnia terrestris Cookson was undertaken to resolve the conflict of opinion regarding the life cycle of fungi in the Saprolegniaceae, i.e., whether meiosis is zygotic or gametic. Microspectrophotometric analysis reveals that pre-divisional oogonial and antheridial nuclei are 4C; a subsequent reduction division in the sex organs produces 1C male and female gametes. These division products coexist in the developing oospore and presumably fuse to produce the diploid zygote. Analysis of the somatic hyphal nuclei shows a 2C DNA content, with the characteristic skew and bimodal character indicative of predominantly G1, and some S-period and G2 types. The evidence is completely consistent with gametic meiosis, i.e., a predominant diploid vegetative phase and short haploid phase, and refutes the notion of zygotic meiosis. Further ramifications of the work are discussed along with preliminary results of related work in progress. THERE is an increasing body of evidence indicating that meiosis occurs during gametogenesis in members of the Saprolegniales and Peronosporales (Trow, 1895, 1899, 1904; Stevens, 1899; Sansome, 1961, 1963, 1965; Sansome and Harris, 1962; Barksdale, 1966, 1968). Collectively this evidence is in favor of such an interpretation. However, no report has been presented which is, in itself, entirely convincing. The occurrence of gametic meiosis in members of the Saprolegniales was first reported by Trow (1895, 1899, 1904) and in members of the Peronosporales by Stevens (1899). Two years later Stevens (1901) stated that a reduction in chromosome number during gametogenesis was improbable in those fungi he had studied. In the next 50 years numerous reports were made of the occurrence of one mitotic division rather than two divisions of meiosis in the sex organs of the Oomycetes (see Barksdale, 1968). Schrader (1938) and Ziegler (1953) claimed that meiosis occurred in the germinating oospore of members of the Saprolegniaceae. In spite of the generally accepted view of zygotic meiosis in this group of fungi, the question was again raised through the efforts of Sansome (1961, 1963, 1965) and Sansome and Harris (1962). The observations of these investigators on the gametangial nuclei of several species of Oomycetes may be summarized as follows: (1) Two successive divisions occur with an associated reduction in nuclear size. (2) The number of IReceived for publication 17 February 1969. Research supported by Office of General Research, University of Georgia, Athens 30601. 2Present address: Division of the Sciences, Kirklani College, Clinton, N.Y. 13323. nuclei in the gametangia following the second division are approximately four times the number of nuclei undergoing the first division. (3) Chromosomal configurations with loops are present in early anaphase figures. (4) Irregularities in chromosomal behavior occur such as early separation or failure of pairing. (5) Typical metaphase figures are present only in the gametangia. (6) Multiple associations of more than two chromosomes (e.g., trivalents and quadrivalents) occur. (7) A bridge and fragment are present occasionally in first division anaphase nuclei. Clearly this evidence is substantial. Nonetheless the nuclei of these fungi are small, and as a result the photomicrographs presented in support of these observations are not convincing. Supporting her own contentions, Sansome (1963, 1965) aptly points out that Ziegler's (1953) illustrations of the metaphase nuclei in the oogonia of Achlya recurva show considerably larger chromosomes than the supposed meiotic metaphase chromosomes in the oospore drawn at the same magnification. Further doubt is cast upon Ziegler's (1953) observations since the zygote nucleus in sectioned material is clearly illustrated by Ziegler (p. 62Fig. 8, Fig. 24; p. 64: Fig. 34) as being situated within the ooplast (Moore and Howard, 1968), a vacuolar-like region of the oospore, rather than within the organelle-containing cytoplasm. Mullins and Raper (1965) present genetic evidence which suggests that meiosis is gametic in Achlya ambisexualis and Dictyuchus monosporus. However, as pointed out by Mullins and Raper (1965), their results are also consistent with a zygotic meiosis followed by the survival of a single meiotic product.
TL;DR: A direct correlation was found between observed DNA absorbance and chromosome number except for plants of B. papyrifera with 84 somatic chromosomes, which may be an adaptation for the establishment of higher ploidy in birches.
Abstract: Relative amounts of DNA were determined on telophase nuclei by Feulgen cytophotometry for euploid taxa of birch (Betula) with somatic chromosome numbers of 28, 42, 56, 70, and 84. A direct correlation was found between observed DNA absorbance and chromosome number except for plants of B. papyrifera with 84 somatic chromosomes. The DNA density value for nuclei of the 84-chromosome plants fitted a 1∶2.25 ratio instead of the expected 1∶3.0 ratio. The DNA density value for these plants was calculated to be approximately equivalent to plants which would possess 63 somatic chromosomes. The average DNA value per chromosome was 2.73 for the 84-chromosome plants in contrast to 3.50 per chromosome in each of the lower euploids. Nuclear diameters of the 84-chromosome plants were directly related to chromosome number and not to DNA density value. The genomic number of Betula was considered to be x=7, rather than x=14, since a DNA value equivalent to 63 chromosomes is a multiple of 7 and not 14. Diploid birch species (2n=2x=28), therefore, would actually be tetraploids (2n=4x=28). The reduction in DNA content may be an adaptation for the establishment of higher ploidy in birches.
TL;DR: Forty-two mutants of the anther smut fungus Ustilago violacea were mapped by means of complementation tests, mitotic haploidization, and meiotic segregation, and the genetical evidence for a haploid chromosome number of at least 10–12 is in conflict with the observations of several cytologists that n = 2.
Abstract: Forty-two mutants of the anther smut fungus Ustilago violacea were mapped by means of complementation tests, mitotic haploidization, and meiotic segregation. Spontaneous mitotic haploidization was very rare, but haploids were induced at a high frequency using p–fluorophenylalanine (PFP). Haploid segregants appeared as fast-growing, spherical colonies (papillae) which grew away from the diploid growth on PFP medium. Thirty-three markers, classified by complementation tests into 21 genes, were mapped by mitotic haploidization in 10–12 linkage groups. There were no discrepancies in the linkage data, and all the markers could be assigned unequivocally to linkage groups. Although about 250 diploids were analysed, there were no segregants in which mitotic crossing-over and mitotic haploidization appeared to have occurred simultaneously.Thirteen of the 33 markers, in six or seven genes, were expressed infrequently (0–5%) in the papillae produced on PFP medium. These markers, which behaved unusually and were designated missing-markers, were found to be on two chromosomes which tended to remain disomic on PFP medium. Thus 8–10 chromosomes haploidize readily on PFP medium, whereas two other chromosomes are resistant to the effects of PFP and remain disomic. Meiotic segregation was investigated in crosses of genetically marked haploid stocks and also hi diploids, using the host plant. Some of the results enabled preliminary maps to be made of three linkage groups. The results from meiotic segregation were fully compatible with those from mitotic haploidization and the complementation tests.The genetical evidence for a haploid chromosome number of at least 10–12 is in conflict with the observations of several cytologists that n = 2 in this species.
TL;DR: Echymipera kalabu (Peramelidae: Marsupialia) does not have the full chromosome complement in all its adult somatic tissues, and a parallel mosaicism to this exists with respect to small supernumerary chromosomes which are found in certain animals of this species.
Abstract: Echymipera kalabu (Peramelidae: Marsupialia) does not have the full chromosome complement in all its adult somatic tissues. The chromosomes missing are the Y-chromosome in the male and an X-chromosome in the female. The full complement is present in the corneal epithelium and the reproductive tissue. A parallel mosaicism to this exists with respect to small supernumerary chromosomes which are found in certain animals of this species. These supernumeraries must be subject to the same control system as that which is responsible for the elimination of the sex chromosomes.
TL;DR: The chromosomes were studied in five species of cobitiid loaches with the application of current air-drying techniques and it was found that Misgurnus anguillicaudatus, Barbatula toni, Lefua nikkonis and Cobitis delicata had the same diploid number of 50.
Abstract: The chromosomes were studied in five species of cobitiid loaches with the application of current air-drying techniques. It was found that Misgurnus anguillicaudatus, Barbatula toni, Lefua nikkonis and Cobitis delicata had the same diploid number of 50. Comparison of karyotypes revealed the chromosome morphology characteristic of each species. In contrast, Cobitis biwae was remarkable by having 96 chromosomes. No evidence for sexual difference of chromosomes was obtained in the species studied here.
TL;DR: It has been suggested that meiotic abnormality is not the cause of pollen degeneration in the material studied and a segmental allopolyploid origin of the present day cultivars of cassava has be suggested.
Abstract: Detailed analyses of chromosomes at pachytene and later stages of meiosis were made in a cultivated type of cassava Pachytene chromosomes are depicted on the basis of total length, relative length, arm ratio, amount and distribution of heterochromatin and number and position of chromomeres Idiograms showing details of all the eighteen pachytene bivalents in the haploid complement are presented and based on the average values of lengths obtained by accurate measurements of the bivalents in a minimum of 15 completely analyzable nuclei, the eighteen pachytene bivalents have been arranged and numbered in order of their decreasing length as chromosome I to chromosome XVIII The haploid chromosomal complement, inter alia, has three functional nucleolar chromosomes and six chromosomal types represented in duplicate Based on the data of the pachytene karyology obtained, a segmental allopolyploid origin of the present day cultivars of cassava has been suggestedBased on cytological data, it has been suggested that meiotic abnormality is not the cause of pollen degeneration in the material studied
TL;DR: It is concluded from this that both cessation of growth in cells of fixed size and the timing of mitoses in coencytes are determined by a critical volume of cytoplasm per genome, rather than per nucleus.
Abstract: SUMMARY: Diploid conidiospores of Aspergillus nidulans are uninucleate and have twice the volume of haploid conidiospores. On the other hand, the hyphae are coenocytic, and it has been found that the dimensions of the hyphal cell are unaffected by ploidy but that diploid cells have half as many nuclei as haploid ones. It is concluded from this that both cessation of growth in cells of fixed size and the timing of mitoses in coencytes are determined by a critical volume of cytoplasm per genome, rather than per nucleus.
In the conidial apparatus, the dimensions of the coenocytic conidiophore, like the hyphae, are unaffected by ploidy, while the uninucleate sterigmata are larger in the diploid. In the case of the primary sterigmata, however, the volume in the diploid is less than twice that in the haploid, suggesting that the mechanism controlling cytoplasmic volume is not fully operative at this stage.
TL;DR: The presence of a chromosome bearing a sub-terminal centromere within the complement of the Amazon molly provides the only direct evidence to date of centric shifts within the chromosome complements of the subgenus Poecilia.
Abstract: Cytological studies of fish from the subgenus Poecilia (Pisces) including members of an all-female species, P. formosa, have clearly shown diploid, somatic chromosome complements and Robertsonian arm numbers of 46. A triploid somatic chromosome complement of 3N = 69 was demonstrated for members of a naturally occurring variant clone of P. formosa, a form whose general body morphology closely resembles that of its sympatric species P. mexicana. Chromosomes of the different poeciliid species studied are remarkably similar in size, shape and structure, being mostly short acrocentrics, 2 μ long or less.The presence of a chromosome bearing a sub-terminal centromere within the complement of the Amazon molly provides the only direct evidence to date of centric shifts within the chromosome complement of the subgenus Poecilia. This finding also provides the first plausible cytogenetic basis for concluding that P. formosa is of relatively recent origin. Comparisons of relative chromosome lengths from both mitotic a...
TL;DR: It is reported that mouse spermatozoa of the genotype H-2d absorb specific H- 2d antibodies, and whether the diploid prereduction or haploid postreduction activity of theH-2 locus is responsible for the presence of H-1 antigens on spermutozoa remains to be elucidated.
Abstract: THE view that the phenotype of mammalian gametes does not reflect their haploid genotype but rather the gene content of their diploid parent still predominates in mammalian genetics. But the differential melanizing activity, in the presence of dihydroxyphenylalanine, of spermatozoa from rabbits of different coat-colour genotypes1 suggests haploid gene action in mammalian gametes. And the very irregular transmission ratios of some alleles of the T-locus (brachyury) in the mouse provide very clear examples of gene action in spermatozoa2,3. These findings justified a search for further evidence on gene action in mammalian spermatozoa. Histocompatibility antigens might be suitable markers of such action; they are present on the membrane of many types of mammalian cells, probably associated with general cell physiology rather than with specific functions of differentiated cells. Here we report that mouse spermatozoa of the genotype H-2d absorb specific H-2d antibodies. Whether the diploid prereduction or haploid postreduction activity of the H-2 locus is responsible for the presence of H-2 antigens on spermatozoa remains to be elucidated.
TL;DR: The sex chromosomes segregate precociously in prometaphase I of male meiosis, without prior synapsis or any physical connection, in 4 species of American mantispids (Neuroptera: Mantispidae).
Abstract: The sex chromosomes segregate precociously in prometaphase I of male meiosis, without prior synapsis or any physical connection, in 4 species of American mantispids (Neuroptera: Mantispidae). Segregational movements are interpolar, and are implemented through chromosomal fibers. Univalent autosomes, present from diakinesis on in several species, are capable of a similar distance segregation in prometaphase. The sex chromosomes are XX ♀ —XY ♂, as is characteristic of the Order, with the exception of Entanoneura phthisica in which both elements are compound —X1X2X3Y1Y2Y3in the male, and X1X1X2X2X3X3 in the female. In tetraploid sectors of gonial origin in testes of this species no sex bivalents are formed; a distance segregation of 6 sex univalents to each pole is effected, but — as observed in the one individually identifiable pair — segregation separates complete homologues, Y1 from Y1, X1 from X1, etc. In all species the male meiotic spindle is formed by the collocation of individual chromosomal spindle units within which bivalents become deformed; the timing and degree of deformation vary with the species. In karyotype the American species conform to a common pattern with the known Japanese and European species; diploid numbers range only from 18 to 22, and each complement carries the family insigne of one pair of disproportionately large autosomes in a set of small and rather uniformly sized chromosomes.
TL;DR: The chromosomes of a Burkitt lymphoma case were followed through a period of three months, including stages before treatment and during treatment and progression, finding a difference characterized both the facial tumors and the neck metastases.
Abstract: The chromosomes of a Burkitt lymphoma case were followed through a period of three months, including stages before treatment and during treatment and progression. The patient had bilateral facial tumors with metastases to lymph nodes on either side of the neck. The chromosomal stemlines were different on the left and the right side. Both were diploid, the left side representing the normal karyotype, the right side exhibiting a number of marker chromosomes. This difference characterized both the facial tumors and the neck metastases.
During early stages of the right-side tumor, the marker chromosomes M2 and MC predominated. Both were derived from C group chromosomes and had a constriction on their longer arm, separating a distal segment from the rest of the chromosome. M2 had the appearance of a small No. 2 chromosome, MC that of a large C chromosome. Later on, M2 was replaced by M1 through translocation of the distal segment to a No. 1 chromosome. Two other marker chromosomes MB and MD resembled B and D chromosomes, respectively, with elongated long arms.
At terminal stages of the disease, when chemotherapeutic treatments had been administered repeatedly, highly disturbed chromosome conditions prevailed with numerous signs of chromosome breakage and errors of spiralization. Also a cultured cell line established at an early stage from the right-side tumor showed a high incidence of similar aberrations. All the marker chromosomes, except, M1, were recovered in the culture.
TL;DR: The following conclusion may be reasonably drawn as far as wheat and its relatives are concerned: appreciable changes of DNA content might have resulted from chromosome aberrations accumulated in the course of genome differentiation of a common primitive genome at the diploid level.
Abstract: 1. Comparisons were made of DNA content per nucleus in common wheat, artificially synthesized 6x wheat, its parental species and three analyzers.2. DNA content per nucleus in the D genome analyzer was the lowest, B genome had a little lower DNA content than A genome, but the difference between the last two was not significant.3. Ssp. strangulata had a significantly higher DNA value than var. typica of the same species, Ae. squarrosa.4. Two strains of synthesized 6x wheat, ABD No. 1 and ABD No. 13, have nuclear DNA equal to the sum of the DNA contents of their respective parents. Nuclear DNA content of cultivated common wheat (Chinese Spring) is quite the same as that of synthesized 6x wheat, especially ABD No. 13.5. In three subspecies of T. aestivum, vulgare, spelta and macha no significant difference was found in DNA content per nucleus.6. Based on the above facts, the following conclusion may be reasonably drawn as far as wheat and its relatives are concerned:a) Appreciable changes of DNA content might have resulted from chromosome aberrations accumulated in the course of genome differentiation of a common primitive genome at the diploid level.b) The three different genomes, once established, have been appreciably stable and kept the amount of DNA constant either in diploid or polyploid condition.
TL;DR: Treated cultures of human fetal fibroblasts showed an incidence of chromosomal aberrations and percentages of aberrant cells that did not differ from the values obtained in untreated control cultures.
Abstract: Diploid cultures of human fetal fibroblasts were treated with various concentrations of chlordiazepoxide and of diazepam, with exposure times ranging from 8 h to 4 days. At termination of treatment, the chromosomes of the cells were prepared and analyzed with respect to chromosome damage. In all experiments, treated cultures showed an incidence of chromosomal aberrations and percentages of aberrant cells that did not differ from the values obtained in untreated control cultures.
TL;DR: The three electrophoretic variants of phosphoglucomutase in Saccharomyces cerevisiae breeding stocks are produced by two unlinked genes, pgm-1 and pgM-2.
Abstract: The three electrophoretic variants of phosphoglucomutase in Saccharomyces cerevisiae breeding stocks are produced by two unlinked genes, pgm-1 and pgm-2; pgm-1 contains two known alleles, pgm-1a and pgm-1b, each of which specifies a minor phosphoglucomutase component, and pgm-2 specifies the major phosphoglucomutase component.
TL;DR: Evidence is provided that pulverization, incomplete condensation, as well as some varieties of enhanced secondary constrictions form a spectrum of changes characterized by their spontaneous occurrence in permanent cell lines of several species and by DNA synthesis in G2.
Abstract: An appearance suggesting extreme fragmentation of chromosomes has been referred to as \"pulverization\" by Nichols et al. (1). A different appearance, that of accentuated secondary constrictions (or chromomeres), was described by Stubblefield in a Chinese hamster cell line, Don (2). In 1967 zur Hausen (3) described an appearance more often occurring in chromosome No. 1 and referred to as \"incomplete condensation.\" The incompletely condensed segments were shown to synthesize DNA after the normal segments had ceased replication. Subsequently, both Nichols et al. (4) and Kato and Sandberg (5) have reported that pulverized chromosomes exhibit a similar asynchrony. The present report will provide evidence that pulverization, incomplete condensation, as well as some varieties of enhanced secondary constrictions form a spectrum of changes characterized by their spontaneous occurrence in permanent cell lines of several species and by DNA synthesis in G2 .
Journal Article•
TL;DR: Present chromosome data indicate that, among the transplantable Morris rat hepatomas, only six are diploid, and only two have a completely normal karyotype, and regular reexamination seems indicated on those being used for metabolic studies.
Abstract: Summary Present chromosome data indicate that, among the transplantable Morris rat hepatomas, only six are diploid (9618A, 9633, 7794A, 7800, 9121, and 9098), and only two (9618A, 9633) have a completely normal karyotype. Two previously diploid hepatomas (9618B, 9611B) have recently undergone transition to an aneuploid state. Despite the difficulty in obtaining adequate chromosome preparations from the slow-growing tumor lines, regular reexamination seems indicated on those being used for metabolic studies.
TL;DR: The species Solanum chacoense BITT is a tuber-bearing, self-incompatible species which is important both for breeding and for genetic research, and doubles the chromosome number by colchicine makes it a self-compatible autotetraploid.
Abstract: The species Solanum chacoense BITT (2n=2x=24) is a tuber-bearing, self-incompatible species which is important both for breeding and for genetic research It crosses readily with most other tuber-bearing Solanum species including the common potato S tuberosum (2n=4x=48) Gametophytic incompatibility hampers research in and utilization of this species Doubling the chromosome number by colchicine makes it a self-compatible autotetraploid By crossing selfed progeny of 4x-S chacoense with a number of haploid-inducing diploid Solanum species a high yield of different dihaploid S chacoense individuals (2n=24) could be obtained from one originally diploid clone: S chacoense CPC 1153 More than 160 haploids showing a large variability were identified The average haploid frequency was 537 per 100 berries Most hybrid plants (70–100%) from four 4x × 2x crosses studied were tetraploid The frequency of triploid hybrids was low (0–10%) Haploid-inducing capacity of fifteen male parents used in this study varied from 0–141 haploids per 100 berries Careful examination of 156 haploids revealed 15 viable aneuhaploids (2n=25, 26, and 27), ie 94% The potential value of these aneuhaploids is discussed