Showing papers on "Chromosome published in 1978"

Mechanisms of chromosome banding and implications for chromosome structure.

Abstract: INTRODUCTION 25 HlSTONES AND CHROMOSOME BANDING .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 C-BANDING-EXTRACTION OF NON-C-BAND DNA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 G-BANDS=CHROMOMERES OF MEIOTIC CHROMOSOMES 29 MAJOR G-BANDS ARE COMPOSED OF SEVERAL SMALLER CHROMOMERES .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 GIEMSA STAINING-SIDE STACKING OF THIAZIN DYES ON DNA ..... . . . 30 G-BANDING-ENHANCEMENT OF THE CHROMOMERE PATTERN ... . . . . . 3 1 Q-BANDING-DETECTION OF AT-RICH DNA .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 HOECHST 33258 BANDING-DETECTION OF AT-RICH DNA ... . . . . . . . . . . . . . . . . . . . 35 R-BANDING DETECTION OF GC-RICH DNA 35 Qor R-BANDING BASED ON EARLY REPLICATING DNA IN R-BANDS AND LATE REPLICATING DNA IN Qor G-BANDS . . . . . . . . . . . . . . . . . . . . . . 37 CHROMOSOME BANDS DELINEATE THREE TYPES OF CHROMATIN .... 38 IMPLICATION OF CHROMOSOME BANDING FOR CHROMOSOME STRUCTURE 39

Aneuploidy and ageing: chromosome studies on a random sample of the population using G-banding.

Abstract: Chromosome analysis using G-banding was carried out on cells from 65 males and 102 females of all ages from a random sample of the population. The frequency of aneuploid cells showed a significant inc

Chromosomal localization of human β globin gene on human chromosome 11 in somatic cell hybrids

Abstract: We have successfully used a DNA·cDNA molecular hybridization assay to directly determine the presence or absence of human β globin gene sequences in 20 human—mouse somatic cell hybrids, each of which contained a different subset of human chromosomes. The assay is specific for the individual human globin genes and will detect the presence of a globin gene if the relevant chromosome is present in only 10% of the cells of a hybrid population. The content of human chromosomes in each hybrid clone was characterized by Giemsa 11 staining, Giemsa trypsin-Hoechst 33258 staining, and by the use of 22 independent isozyme markers for 17 different human chromosomes. All human chromosomes were present in one or more cell lines devoid of the human β globin gene except for 6, 8, 9, 11, and 13. Among these latter chromosomes, only chromosome 11 was present in the six hybrid clones that contained the human β globin gene. In fact, chromosome 11 was the only human chromosome that was present in all of the six hybrid clones found to be positive for the human β globin gene. Two sister clones, 157-BNPT-1 and 157-BNPT-4, had similar subsets of human chromosomes except that 11 was present only in 157-BNPT-4. 157-BNPT-4 contained the human β globin gene while 157-BNPT-1 did not. DNA from three hybrid lines was also annealed to purified human γ globin cDNA; two lines positive for human β globin gene sequences also contained human γ globin gene sequences while one line was negative for both β and γ gene sequences. On the basis of these results, the human β and γ globin genes have been assigned to human chromosome 11.

B-A translocations in maize I. Use in locating genes by chromosome arms

Abstract: HE B-A TRANSLOCATIONS of maize (Za mayvs L.) provide a most efficient method for T locating recessive mutants to the proper chromosome arm. More comprehensive knowledge of gene location should permit efficient assembly of genotypes for improving photosynthetic rate and disease reaction and for other practical goals.

Assignment of genes to regions of mouse chromosomes.

Abstract: A genetic mapping procedure, called the duplication-deficiency method, is described. This method permits the genetic location of a translocation to be determined within a linkage group without the use of recombination. By utilizing the duplication-deficiency method to define the genetic breakpoints for a series of translocations involving a given chromosome and integrating this information with their cytological breakpoints, obtained by Giemsa banding, a genetic map of the chromosomes is constructed whereby groups of loci are assigned to banded regions. Duplication-deficiency mapping and Giemsa banding analysis of the T(X;7)1Ct and T(7;19)145H translocations together with information from the c25H deletion have permitted mouse chromosome 7 to be divided into six and chromosome 19 into two definable genetic regions.

Heterochromatin and highly repeated DNA sequences in rye (Secale cereale)

Abstract: Secale cereale DNA, of mean fragment length 500 bp, was fractionated by hydroxylapatite chromatography to allow recovery of a very rapidly renaturing fraction (C0t 0–0.02). This DNA fraction was shown to contain several families of highly repeated sequence DNA. Two highly repeated families were purified; (1) a fraction which renatured to a density of 1.701 g/ cc and comprised 2–4% of the total genome, and (2) polypyrimidine tract DNA which comprised 0.1% of the total genome. The 1.701 g/cc DNA consisted of short sequence repeat units (5–50 bp long) tandemly repeated in blocks 30 kb long, while a portion of the polypyrimidine tract DNA behaved as part of a much larger block of tandemly repeated sequences. The chromosomal location of these sequences was determined by the in situ hybridisation of radioactive, complementary RNA to root tip mitotic chromosomes and showed the 1.701 g/cc sequences to be largely limited to the telomeric blocks of heterochromatin, accounting for 25–50% of the DNA present in these parts of the chromosomes. The polypyrimidine tracts were distributed at interstitial locations with 20–30% of the sequences at three well defined sites. The combined distributions of the 1.701 g/cc DNA sequences and polypyrimidine tracts effectively “individualised” each rye chromosome thus providing a sensitive means of identifying these chromosomes. The B chromosomes present in Secale cereale cv. Unevita, did not show defined locations for the sequences analysed. — The data are discussed in terms of the structure of the rye genome and the generality of the observed genomic arrangement of highly repeated sequence DNA.

Cytogenetical studies in wheat

Abstract: Two genes for resistance to Puccinia graminis f. sp. tritici were located in chromosome 2B of Kota wheat. Both were mapped in the long arm. The first designated Sr28 was situated distally to Sr9 and showed 34·6±2·8 per cent recombination with the centromere. The second gene, which was not definitely distinguished from Sr16 either on the basis of recombination or by its response to several pathogen cultures, was inherited independently of the 2B centromere and of Sr9, but showed 38·2±1·9 and 29·2±4·2 per cent recombination with Sr28. Comparisons of present results with those from earlier studies suggested that Kota possesses at least five genes for resistance.

Genetic studies on heterochromatin in Drosophila melanogaster and their implications for the functions of satellite DNA

Abstract: In Drosophila melanogaster the centromeric heterochromatin of all chromosomes consists almost entirely of several different satellite DNA sequences. In view of this we have examined by genetic means the meiotic consequences of X chromosomes with partial deletions of their heterochromatin, and have found that the amount and position of recombination on each heterochromatically deleted X is substantially different from that of a normal X. It appears that the amount of heterochromatin is important in modifying the "centromere effect" on recombination.--In all the deleted Xs tested, chromosome segregation is not appreciably altered from that of a nondeleted control chromosome. Thus satellite DNA does not appear to be an important factor in determining the regular segregation of sex chromosomes in Drosophila. Additionally, since X chromosomes with massive satellite DNA deficiencies are able to participate in a chromocenter within salivary gland nuclei, a major role of satellite DNA in chromocenter formation in this tissue is also quite unlikely.--In order to examine the mechanisms by which the amount of satellite DNA is increased or decreased in vivo, we have measured cytologically the frequency of spontaneous sister chromatid exchanges in a ring Y chromosome which is entirely heterochromatic and consists almost exclusively of satellite DNA. In larval neuroblast cells the frequency of spontaneous SCE in this Y is approximately 0.3% per cell division. Since there is no meiotic recombination in D. melanogaster males and since meiotic recombination in the female does not occur in heterochromatin, our results provide a minimum estimate of the in vivo frequency of SCE in C-banded heterochromatin (which is predominantly simple sequence DNA), without the usual complications of substituted base analogs, incorporated radioactive label or substantial genetic content.--We emphasise that: (a) satellite DNA is not implicated in any major way in recognition processes such as meiotic homologue recognition or chromocenter formation in salivaries, (b) there is likely to be continuous variation in the amount of satellite DNA between individuals of a species; and (c) the amount of satellite DNA can have a crucial functional role in the meiotic recombination system.

Chromosome Changes (Trisomies #15 and 17) Associated With Tumor Progression in Leukemias Induced by Radiation Leukemia Virus

Abstract: An experimental system was developed that permitted nonrandom chromosome changes that occur in radiation leukemia virus (RadLV)-induced lymphomas to be followed during tumor progression. RadLV variant-induced preleukemia and leukemia cells originating from female inbred C57BL/6 mice were injected into male animals of the same strain. Since all donors were females and all recipients were males, the sex chromosome complements (XX and XY) were used to distinguish the preleukemia and leukemia cells from those of host origin. The G-banding analysis revealed that more than 50% of animals that were inoculated with preleukemia cells and that developed leukemia possessed tumor stem-lines of 41 chromosomes with a tristomy of chromosome #15. In animals inoculated with overt leukemia cells and in which tumor progression occurred, the G-banding an additional trisomy of chromosome #17. The cytogenic data strongly suggested that the trisomy of chromosome #15 was the first specific tumor-associated chromosome change that occurred in the process of conversion of RadLV-induced preleukemia cells to fully autonomous tumor cells.

Conservation of autosomal gene synteny groups in mouse and man

Abstract: WHILE genes on the X chromosome have been conserved during evolution1 little is known about the degree of conservation of autosomal synteny groups for species distantly related in evolution such as mouse and man. The mouse gene map based on sexual genetics2,3 has been expanded by analysis of interspecific somatic cell hybrids segregating mouse chromosomes, so that the genetic maps of man and mouse can be compared. The available information indicates that genes located on different arms of the same human chromosome are not syntenic in the mouse, and genes which are many map units apart (25–45 cM) in the mouse are unlikely to be syntenic in man4–6. In contrast, genes that are tightly linked (less than 1 cM apart) seem to remain syntenic during evolution5. In addition, in species closely related in evolution, such as mouse and rat,7 or man and non-human primates8, several homologous genes have been assigned to chromosomes that are apparently homologous by chromosome banding. Five genes in the mouse (Eno-1, Pgd, Pgm-2, Ak-2, Gpd-1) are syntenic9–11 and their human homologues have been assigned to human chromosome 1; all but the human homologue of Gpd-1 are regionally assigned to arm 1p (refs 4 and 12). This apparent conservation of a rather large autosomal synteny group prompted us to investigate the extent of conservation of other autosomal regions. The results have provided chromosomal assignments for seven gene loci in the mouse and evidence for synteny of four pairs of gene loci on four different human and mouse autosomes.

High-resolution chromosome analysis in clinical medicine.

Abstract: The field of human cytogenetics has expanded considerably in the past few years due, to a large extent, to the application of the metaphase banding techniques. Among many advances, the chromosomal abnormalities involved in over thirty newly discovered syndromes have been defined and consistent chromosome defects have been observed in several neoplasias. Very recent improvements in culture techniques through cell synchronization and in chromosome treatments, such as the use of minimal exposure to colcemid and/or the use of agents that inhibit chromosome condensation, allow for the routine utilization of highly elongated and finely banded prophase chromosomes. These new techniques are being used clinically to uncover previously undetectable chromosome defects, to localize the exact break points involved in numerous duplication-deficiencies known in man, and to establish possible phenotype-genotype relationships at a refined level.

Reiterated genes with varying location in intercalary heterochromatin regions of Drosophila melanogaster polytene chromosomes.

Abstract: The localization of two cloned D. melanogaster DNA fragments in polytene chromosomes was determined by means of in situ hybridization. These different fragments (Dm 225 and Dm 234B) are present in the genome in hundreds copies and contain genes whose transcription yields two different classes in abundant mRNA (Ilyin et al., 1976, 1977; Tchurikov et al., 1978). About 20–30 sites of these genes are demonstrable in the polytene chromosomes of a given stock. There are small but significant variations in the number and localization of these sites among individuals of the same stock. On the other hand, different stocks of D. melanogaster have an utterly different distribution of revealed hybridization sites in the polytene chromosomes. The location of both fragments (Dm 225 and Dm 234) was found to be virtually identical within any given stock of D. melanogaster. 69 sites for localization of Dm 225 or Dm 234 genes were detected in the chromosomes of 11 individuals studied. At least 50 (and up to 62) of them coincide with intercalary heterochromatin regions which are known to be characterized by ectopic pairing, late replication and the presence of “weak spots” in the chromosome. The ability of Dm 225 and Dm 234 to code for the “abundant” classes of messenger RNA (Ilyin et al., 1976) and the fact that their location may coincide with the histone and ribosomal genes suggest that intercalary heterochromatin regions are “nests” containing various types of actively transcribable tandem-repeated genes coding for common “household” cell functions.

Cytogenetic mapping of the trisomic segment of chromosome 15 in murine T-cell leukaemia.

Abstract: A NONRANDOM cytogenetic change in the form of trisomy of chromosome 15 is associated with mouse T-cell leukaemia induced by various agents, such as Gross, Rad and Moloney leukaemia viruses, X rays and a chemical carcinogen, 7,12-dimethylbenz(a)anthracene (DMBA)1–4. The uniformity of the chromosomal change and its apparent independence of the inducing agent suggest that it plays an important and perhaps decisive part in the neoplastic transformation of the mouse T lymphocyte. During our studies of the role of chromosome 15 and related factors in lymphoma development, we have investigated whether any particular region of the chromosome needs to be duplicated. Using DMBA to induce T-cell leukaemias in mice carrying chromosome 15 translocations, we have found, and now report that the duplicated chromosome segment is located distal to the T6 breakpoint of chromosome 15.

Karyotype analysis in rice

Abstract: Mitotic chromosomes of rice, Oryza sativa L. (2n=24), were all identified by a newly developed technique. A new technique of cell suspending and flame-drying made chromosomes possible to be well flattened and spreaded. Tissue treatment with KCl and enzyme caused segmental differentiation in chromosome stainability with Giemsa. All chromosomes were able to be identified in a single prometaphase nucleus by individual characteristics. Twelve pairs of chromosomes were gradually different in length and composed of 5 metacentrics, 5 sub-metacentrics and 2 sub-telocentrics including a satellited pair.

Characterization of a mutation in yeast causing nonrandom chromosome loss during mitosis.

Abstract: Diploid strains of the yeast Saccharomyces cerevisiae homozygous for a recessive chromosome loss mutation ( chl ) exhibit a high degree of mitotic instability. Cells become monosomic for chromosome III at a frequency of approximately one percent of all cell divisions. Chromosome loss at this high frequency is also found for chromosome I , and at lesser frequencies for chromosomes VIII and XVI . In contrast, little or no chromosome loss is found for six other linkage groups tested ( II, V, VI, VII, XI and XVII ). The chl mutation also induces a ten-fold increase in both intergenic and intragenic mitotic recombination on all ten linkage groups tested. The chl mutation does not cause an increase in spontaneous mutations, nor are mutant strains sensitive to UV or γ irradiation. The effects of chl during meiosis are observed primarily in reduced spore viability. A decrease in chromosome III linkage relationships is also found.

Co-transfer of human X-linked markers into murine somatic cells via isolated metaphase chromosomes.

Abstract: Transformation frequencies of 4 × 10-5 were obtained in chromosome-mediated gene transfer experiments using human cell line HeLa S3 as donor and mouse cell line A9 as recipient. This high frequency of interspecific transformation was achieved by treating the recipient cells with dimethylsulfoxide in addition to other facilitators. The high frequency of transformation correlated positively with transgenome size on the basis of both co-transfer of linked markers and chromosome analysis. The syntenic human markers glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate:NADP+ 1-oxidoreductase, EC 1.1.1.49) and phosphoglycerate kinase (ATP:3-phospho-D-glycerate 1-phosphotransferase, EC 2.7.2.3) were sometimes transferred together with the selected X-linked prototrophic marker hypoxanthine phosphoribosyltransferase (IMP: pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) into murine somatic cells. Donor human chromosome material could be demonstrated cytologically in some of the transformed cell lines. Transformants exhibited various rates of loss of the human hypoxanthine phosphoribosyltransferase marker when grown under nonselective conditions. These results reveal a broader range of possible interspecific transgenome sizes than has been recognized in the past. The largest transgenomes consist of cytologically detectable donor fragments and contain syntenic markers that are not closely linked to the selected marker.

The B chromosome of corn.

Abstract: INTRODUCTION ........ ........ . . . . .. . . . . ...... ... 5 PROCESSES CONTROLLED BY THE B CHROMOSOME ........ . .. .. ....... ... 8 Nondisjunction 8 Preferential Fertilization , . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . ,. . . . . . . . . . . . ....... 11 Recombination 12 MOLECULAR AND CELLULAR BIOLOGY . . . . . 13 RELATIONSHIP TO ABNORMAL CHROMOSOME 10 IS APPLICATION OF B CHROMOSOME NONDISJUNCTION TO GENETIC STUDIES 16 Chromosome Mapping 16 Transfer of A Chromosome Segments Between Lines .. 16 Gene Dosage and Gene Imprinling Studies 17 SUMMARY ..... . . . . .. ......... ... . ....... 18

Distribution of heterochromatin in a reconstructed karyotype of Vicia faba as identified by banding- and DNA-late replication patterns

Abstract: 1) The distribution pattern of heterochromatin characterized by Giemsa-banding, Quinacrine-banding and DNA-late replication has been studied in a reconstructed karyotype of Vicia faba with all chromosome pairs interdistinguishable. 2) By means of two Giemsa-banding methods both an interstitial and a centromeric Giemsa-banding pattern are described. The former one comprehends 14 “marker” and 18 “additional” bands of lower but characteristic visualization frequencies. The centromeric Giemsa-banding pattern consists of 7 bands, located in the centromeric and in the secondary constrictions of the metaphase chromosomes. Chromosomes with banding patterns intermediate between the interstitial and the centromeric Giemsa-banding have also been observed. 3) Quinacrine-banding revealed 10–12 brightly fluorescent bands and 1–2 regions of dim fluorescence. Most Q-bands occupy chromosomal positions also characterized by interstitial Giemsa bands. 4) The DNA-late replication pattern, analyzed both by autoradiography and by FPG-technique, revealed 9 late replicating chromosome regions; all of these correspond positionally to the sites of interstitial Giemsa bands. 5) The results are discussed with respect to (a) the relationships between the banding- and the DNA-late replication pattern; (b) banding and heterochromatin characteristics; (c) the correlations between the distribution of chromatid aberrations and special types of heterochromatin. — The patterns of heterochromatin distribution found are in basic conformity with the corresponding patterns reported for the standard karyotype of Vicia faba. The heterochromatin type characterized by both Giemsabanding and late replication is characteristic of all those chromosome regions which after mutagen treatments show up as aberration hot spots. Positional correlations between interstitial Giemsa marker bands and chemically induced isochromatid breaks are indicative of preferential aberration clustering in heterochromatin/euchromatin junctions.

Entrapment of metaphase chromosomes into phospholipid vesicles (lipochromosomes): carrier potential in gene transfer.

Abstract: Transfer of genes from one type of cultured mammalian cell to another by using isolated metaphase chromosomes has been reported with a frequency of one per 106-108 cells. Very recently a rate of 16/106 has been reported with Chinese hamster ovary cells [Spandidos, D. A. & Siminovitch, L. (1977) Proc. Natl. Acad. Sci. USA 74, 3480-3484]. To increase the frequency of gene transfer, we isolated metaphase chromosomes from hypoxanthine guanine phosphoribosyltransferase (HGPRT) positive cells, entrapped them in liposomes, and fused the lipochromosomes with HGPRT-negative cells. Lipochromosomes were prepared with cholesterol and egg lecithin, using isolated metaphase chromosomes from a mouse-human somatic hybrid cell line (A9/HRBC2); the entire X chromosome, including the HGPRT, glucose-6-phosphate dehydrogenase, and phosphoglycerate kinase genes, is the only recognizable human genetic material retained by the hybrids. Enclosure of the chromosomes in the lipid envelope was confirmed by electron and fluorescence microscopy and differential centrifugation. These lipochromosomes were fused with HGPRT- mouse cells (A9) in the presence or absence of polyethylene glycol and transferents were selected in hypoxanthine/aminopterin/thymidine (HAT) medium. The frequency of transfer was at least once per 105 cells, a minimum 10-fold improvement over previous methods. The selected cells contained HGPRT activity similar to the amount found in the A9/HRBC2 cells. Starch gel electrophoresis verified that the observed HGPRT activity in the transferents is due to the human enzyme. Human glucose-6-phosphate dehydrogenase and phosphoglycerate kinase were also identified electrophoretically in the transferents. Karyotyping with C and Q banding did not reveal the presence of the whole human X chromosome or a visible extra fragment of a human chromosome associated with the mouse genome. The biochemical data strongly suggest, however, that transfer of a portion of the human X chromosome has occurred in these transferents. Thus, at least three X-linked genes have been transferred from one cell to another with high frequency, using metaphase chromosomes.

Homologous genes for enolase, phosphogluconate dehydrogenase, phosphoglucomutase, and adenylate kinase are syntenic on mouse chromosome 4 and human chromosome 1p.

Abstract: It is possible to generate interspecific somatic cell hybrids that preferentially segregate mouse chromosomes, thus making possible mapping of mouse genes. Therefore, comparison of the linkage relationships of homologous genes in man and mouse is now possible. Chinese hamster × mouse somatic cell hybrids segregating mouse chromosomes were tested for the expression of mouse enolase (ENO-1; EC 4.2.1.11, McKusick no. 17245), 6-phosphogluconate dehydrogenase [PGD; EC 1.1.1.44, McKusick no. 17220], phosphoglucomutase-2 (PGM-2; EC 2.7.5.1, McKusick no. 17190), and adenylate kinase-2 (AK-2; EC 2.7.4.3, McKusick no. 10302). In man, genes coding for the homologous forms of these enzymes have been assigned to the short arm of human chromosome 1. Analysis of 41 primary, independent, hybrid clones indicated that, in the mouse, ENO-1 and AK-2 are syntenic with PGD and PGM-2 and therefore can be assigned to mouse chromosome 4. In contrast, they were asyntenic with 21 other enzymes including mouse dipeptidase-1 (DIP-1, human PEP-C; EC 3.4.11.*, McKusick no. 17000) assigned to human chromosome arm 1q and mouse chromosome 1. Karyologic analysis confirmed this assignment. These data demonstrate that a large autosomal region (21 map units in the mouse and 51 map units in the human male) has been conserved in the evolution of mouse chromosome 4 and the short arm of human chromosome 1. Identification of such conserved regions will contribute to our understanding of the evolution of the mammalian genome and could suggest gene location by homology mapping.

Sex chromosomes in the sockeye salmon: a y-autosome fusion

Abstract: Chromosomes of 21 sockeye salmon [Oncorhynchus nerka (Walbaum)] from three locations in Washington state were examined. All males had 57 chromosomes, while all females had 58 chromosomes. Both sexes had 104 chromosome arms. It appears that in males of this species the Y chromosome and an autosome have fused to form a metacentric chromosome.

Gene duplication in Saccharomyces cerevisiae.

Abstract: Five indepdendent duplications of the acid-phosphatase (aphtase) structural gene (acp1) were recovered from chemostat populations of S. cerevisiae that were subject to selection for in vivo hyper-aphtase activity. Two of the duplications arose spontaneously. Three of them were induced by UV. All five of the duplication events involved the transpositioning of the aphtase structural gene, acp1, and all known genes distal to acp1 on the right arm of chromosome II, to the terminus of an arm of other unknown chromosomes. One of the five duplicated regions of the right arm of chromosome II was found to be transmitted mitotically and meiotically with very high fidelity. The other four duplicated regions of the right arm of chromosome II were found to be unstable, being lost at a rate of about 2% per mitosis. However, selection for increased fidelity of mitotic transmission was effective in one of these strains. No tandem duplications of the aphtase structural gene were found.

Somatic cell hybridization of Vicia faba+Petunia hybrida

Abstract: Isolated protoplasts of Vicia faba and Petunia hybrida have been fused by the action of Ca++, high pH and, occasionally, PEG. The heterokaryotic stage frequently endured mitotic divisions. Only one cell was found with apparently fusing nuclei. Another heterokaryon showed asynchronous phases in the nuclear cycle. Three hybrid tissues have been identified 50 and 60 days after fusion. One of them could be propagated, is 9 months old and still rapidly proliferating. The fusion hybrids contained predominantly nuclei or chromosomes of one or the other species and a few chromosomes of the second parent. These observations were assigned to chromosome elimination which has been conclusively seen in cells containing nuclei of Petunia-type and one or two chromosomes of Vicia left in the cytoplasm. Breakage of chromosomes was the only type of chromosome mutations found in hybrid tissue.

Assignment of a type I collagen structural gene to human chromosome 7

Abstract: COLLAGEN is the major extracellular protein of the body, and forms the fibres which impart tensile strength to all of its structural elements, including skin, bone, tendon and cartilage. It occurs as a family of molecules with closely related structures but distinctive tissue distributions1. Four types have been described with varying degrees of precision; the most abundant and best studied (type I) is a heteropolymer of three polypeptides, two identical (α1(I)), and a third (α2(I)) which differs slightly in primary structure. Types II-IV are homopolymers of the general formula (α1(X))3, where the designation α1 reflects the close sequence homologies shared with α1(I), although this relationship is only tentative in the case of α1(IV). These collagens are probably the products of at least five non-allelic structural genes, and knowledge of their linkage would be useful in view of their possible origin by duplication and divergence from an ancestral collagen gene. Quantitative variations in the expression of these genes are important in normal tissue development, and defective expression has been implied in two inherited disorders, Ehlers-Danlos IV2 and osteogenesis imperfecta3. The chromosomal assignment of these structural genes is a first step towards discovering their linkage relationship and perhaps towards understanding more about their differential expression. Because collagen is readily synthesised by cells in vitro, the problem of chromosome assignments may be investigated by the techniques of somatic cell genetics. When mouse and human cells are fused, random loss of human chromosomes occur, while the full set of mouse chromosomes is usually retained. Assignment of a gene to the chromosome carrying it can be achieved by examining sets of hybrids for expression of the human gene product and ascertaining the segregation of this phenotype with a particular human chromosome. We have examined a series of human–mouse hybrid clones for the production of collagen and report here the consistent segregation of human collagen with human chromosome 7.

A new chromosome type replacing the double minutes in a mouse tumor.

Abstract: For several years the SEWA mouse ascites tumor has been a carrier of double minute chromosomes (DMs), some 90% of its cells containing from one to several hundred DMs. In one specific subline of this tumor, the cells with DMs had decreased in frequency to less than 5% of the cells. At the same time, the stemline chromosome number had increased from 43 to around 50. This was due to the presence, in addition to the ordinary telocentric chromosomes, of a varying number of medium-sized metacentrics. The fact that these chromosomes deviated from ordinary mouse chromosomes in special features, such as median centromeric position, early DNA replication, and complete lack of centromeric heterochromatin, indicates that they represent a new type of chromosome. Their striking agreement with the DMs in many properties makes it tempting to associate their origin with the disappearance of the DMs.

Base ratio, DNA content, and quinacrine-brightness of human chromosomes

Abstract: Human chromosomes were labeled with base-specific radioactive DNA precursors and examined autoradiographically to measure their DNA content and base ratio (percentage A-T base pairs). The requirement that incorporation of labeled bases be uniform during DNA synthesis was met by the use of inhibitors of de novo synthesis of DNA precursors. The genome was subdivided into 75 segments based on quinacrine banding, and the base ratio of each was calculated by a method that corrects for bias due to the scatter of grains about their source. Estimates of base ratio are shown to be sufficiently precise to detect variability among chromosomes and among segments within a chromosome. Analysis of these data and of measurements of the quinacrine fluorescence intensity of segments leads to the following conclusions. Base ratio is positively correlated with brightness, as predicted from independent in vitro studies. Larger chromosomes tend to have higher base ratios and to be brighter than smaller ones. The best prediction of the brightness of a segment must take into account not only its base ratio but also its DNA content. To explain these results, we suggest an evolutionary model in which chromosomes containing repeated sequences of A-T-rich DNA tend to grow by means of unequal sister chromatid and meiotic exchanges.

Abnormalities of chromosome No. 1: significance in malignant transformation.

Abstract: Studies of human hematologic malignancies have provided sufficient data not only for the identification of nonrandom abnormalities of whole chromosomes, but also for determination of the specific chromosome regions involved. In clonal aberrations leading to an excess of chromosome No. 1, or a partial excess of No. 1, trisomy for bands 1q25 to 1q32 was noted in the myeloid cells obtained from every one of 35 patients who had various disorders, such as acute leukemia, polycythemia vera, or myelofibrosis. Similar chromosome changes were a consistent finding in various solid tumors as well. This rearrangement was not the result of a particularly fragile site in that region of the chromosome, since the break points in reciprocal translocations that involve No. 1 occurred almost exclusively in the short arm. The nonrandom chromosome changes found in neoplastic cells can now be correlated with the gene loci on these chromosomes or chromosome segments as an attempt is made to identify specific genes that might be related to malignancy.

Use of the 5-bromodeoxyuridine-labelling technique for exploring mechanisms involved in the formation of chromosomal aberrations I. G2 experiments with root-tips of Vicia faba

Abstract: Chromosomes in root-tip cells of Vicia faba were exposed in the G2 phase to long-wave (320–380 nm) ultraviolet radiation and to X-rays. Before exposure, 5-bromouracil had been substituted for thymine in various numbers of DNA strands in these chromosomes. The experiments involved cells with chromosomes of the following constitutions: TT—TT (both chromatids of the chromosome containing unsubstituted DNA), TT—TB (one chromatid with unsubstituted DNA and one with unifilarly substituted DNA), TB—TB (both chromatids containing unifilarly substituted DNA) and TB—BB (one chromatid with unifilarly and one with bifilarly substituted DNA). The sister chromatids in chromosomes of the TT—TB and TB—BB constitution could be distinguished by differential staining with the FPG technique. Long-wave UV induced no aberrations in chromosomes with unsubstituted DNA. In chromosomes with 5-bromouracil-substituted DNA, long-wave UV, like X-rays, induced sub-chromatid and chromatid aberrations. Because these aberrations were found in the first mitosis after exposure of G2 cells, the effect of long-wave UV was of the S-independent, ionizing type. The sensitivity to the production of aberrations by X-rays increased with increasing number of 5-bromouracil-substituted DNA strands, i.e. TT—TT The results of both the UV and the X-ray experiments clearly indicate that two lesions are required to produce one exchange, thus providing direct evidence in support of an indirect conclusion arrived at long ago on the basis of the dose—effect relationship for radiation-induced exchanges.