Showing papers on "Karyotype published in 1977"

Microcell-mediated transfer of murine chromosomes into mouse, Chinese hamster, and human somatic cells.

Abstract: In this report, we describe the production and characterization of proliferating hybrid cell populations generated by fusion of murine microcells with intact mouse, Chinese hamster, and human recipient cells. The microcell hybrids so produced contained one to five intact murine chromosomes derived from the microcell donor. these transferred chromosomes were maintained as functioning genetic elements in the hybrid cells. Our results firmly establish subnuclear particle-mediated chromosome transfer as a valid somatic cell genetic tool.

Karyotype evolution in Australian ants

Abstract: 105 Australian ant species, including members of the important primitive genera Amblyopone and Myrmecia, were karyotyped using a C-banding air-drying technique. The observed haploid numbers in this survey ranged from 2n=84 (the highest known in the Hymenoptera) to 2n=9. Seven types of chromosome rearrangement were detected, namely: Robertsonian rearrangements, pericentric inversions, saltatory changes in constitutive heterochromatin, simple reciprocal translocations, complex translocations accompanied by significant loss of euchromatin, supernumerary (B-) chromosome variation, and chromosome deletion. Most ant karyotype evolution is explicable in terms of the first three of these. No evidence was found for polyploidy or centric dissociation being of evolutionary significance in ants. The C-band analysis supports a model in which pericentric inversions converting acrocentrics to other types greatly predominate over those with reverse effects. There appears to be little, if any, correlation between whether a species is morphologically primitive or advanced and its karyotype organization. The data provide little support for the ancestral chromosome number in ants having been high with subsequent reduction (“fusion hypothesis”), but rather suggest that the ancestral number was either very low with subsequent increase (“fission hypothesis”) or coincident with the present mode (“modal hypothesis”). Moreover, for these ant data, the modal hypothesis is interpretable as a subset of the fission hypothesis.

Chromosomes and causation of human cancer and leukemia. XXVI. Banding studies in acute lymphoblastic leukemia (ALL)

Abstract: Chromosomes were studied in the bone marrow cells of 101 patients with acute lymphoblastic leukemia (ALL) hospitalized at or attending the clinics of Roswell Park Memorial Institute (RPMI) between January, 1968, and December, 1976. Aneuploidy was observed in about 50% (54/101) of the cases. Two cases were hypodiploid and the remaining were either pseudo or hyperdiploid. The frequency of abnormalities and the chromosomal numbers were similar to those of 106 cases studied in our laboratory prior to 1968. Of 50 recently unselected cases of ALL in whom Q- and G-banded karyotypes were attempted, 31 were successfully analyzed with these techniques. The banding patterns revealed 16 cases to have chromosome abnormalities and four of these to have a similar abnormality, i.e., partial deletion of the long arm of chromosome no. 6: two cases had a 6q- with additional abnormalities and two had 6q- as the sole karyotypic abnormality. The breakpoint in chromosome no. 6 seemed to involve a segment from q21 to q25. An isochromosome of the long arm of no. 7, i(7q), was observed in two cases, two additional no. 21 chromosomes were observed in five cases and, except for the Y, all other chromosomes participated in the karyotypic changes encountered in the 16 cases in which banding analyses were performed. Banding analysis has afforded the first reliable approach towards ascertaining karyotypic evolution in ALL, which was achieved in eight cases of the present study. The chromosomes contributing to this karyotypic evolution were distributed widely. Thus, all chromosomes except the Y participated in numerical and/or structural karyotypic changes. Even though nonrandom chromosome changes may occur early in ALL, the pristine prototypic picture of the karyotypes in ALL is often obfuscated by successive chromosomal changes and hyperdiploidy by the time the karyotypes are analyzed in this condition. Further cytogenetic studies are required, with special attention to karyotypic evolution, in order to uncover the significance of chromosomal changes in early and late ALL.

Double minute chromosomes and the homogeneously staining regions in chromosomes of a human neuroblastoma cell line

Abstract: Four human neuroblastoma cell lines were studied by chromosome banding techniques. All of the lines contained a marker chromosome with a long nonbanding homogeneously staining region (HSR). The HSR-containing chromosome differed in each line. One line contained two classes of cells: one with an HST marker chromosome and the other with double minute chromosomes. Each cell had one of these abnormalities; no cell had both. The presence of two additional chromosomal markers in all cells of this line indicates a common origin. These observations suggest that the double minute chromosomes are derived from the HSR.

Heteromorphic sex chromosomes in male rainbow trout

Abstract: A pair of subtelocentric chromosomes differs in the size of the short arm in male, but not female, rainbow trout (Salmo gairdneri). The morphological similarity of the X and Y chromosomes, and the observation of Y chromosomes intermediate between the X and normal Y, suggest that the sex chromosomes are at an early stage of differentiation in this species.

Correlation of DNA distribution abnormalities with cytogenetic findings in human adult leukemia and lymphoma

Abstract: Pulse cytophotometric analysis of bone marrow cells from 175 patients with leukemia or lymphoma showed abnormalities of cellular DNA distribution in 29 patients for an overall incidence of 16.6%. Comparative standard cytogenetic examination indicated that high-degree chromosomal aberrations (≤44, ≥53 chromosomes) can generally be detected on DNA histograms, whereas patients with diploid, pseudodiploid, 45-hypodiploid, and 47-hyperdiploid abnormalities usually escape recognition by this technique. There were 11 patients with normal diploid or near-diploid karyotypes exhibiting marked DNA deviations; this discrepancy may reflect lack of proliferation of some leukemic clones which is a prerequisite for cytogenetic identification.

Frequency of satellite association of human chromosomes is correlated with amount of Ag-staining of the nucleolus organizer region.

Abstract: Methaphase chromosomes from karyotypically normal adult humans (three males, six females) and one male with a 13p - chromosome were stained by quinacrine and then by the Ag-AS silver staining method to reveal nucleolus organizer regions (NORs). Each person had a characteristic number of Ag-stained chromosomes per cell, always fewer than 10. Determination of the mean Ag-size of each chromosome showed that each of the 10 individuals had a unique distribution of Ag-stain. Within each individual, there was some variation from cell to cell in the number of acrocentric chromosomes that were Ag-stained; this was not random, and the same chromosomes (those that had at most a small amount of Ag-stain) tended to be unstained in every cell. Satellite associations were scored on the same cells. Chromosomes that had no Ag-stain were involved in satellite association less than 20% as often as those that had some Ag-stain. Chromosomes that had a small amount of Ag-stain were involved in association about 50% as often as those that had a large amount of stain. Regression analysis of the 50 (of a total of 100) acrocentric chromosomes which could be individually identified by quinacrine markers showed that the frequency with which a chromosome was involved in satellite association was strongly correlated with the amount of Ag-stained material in the NOR.

Chromosome Stability in CHO Cells

Abstract: The established cell line derived many years ago from Chinese hamster ovary (CHO cells) has been studied for the extent of chromosomal variation. Because this cell line is used extensively for genetic studies, the contribution of chromosome variability to genetic variability has also been examined. The quasidiploid CHO cells were found to have a banded karyotype somewhat altered from that of the Chinese hamster from which the line was derived. However, most of the genome could be accounted for among the rearranged marker chromosomes. In addition, the CHO line was found to have a relatively stable karyotype, the same basic karyotype being found in a majority of the uncloned cells, as well as in most cells of several but not all independent clones. Many, but not all, mutant cell lines derived from CHO also showed the same basic karyotype. Quasitetraploid cells, derived either spontaneously or by Sendai-virus-induced fusion, showed considerably more variation resulting in loss or gain of whole chromosomes, rearrangement of chromosomes, and appearance of new “marker” chromosomes.

Chromosomal abnormalities and their specificity in human neoplasms: an assessment of recent observations by banding techniques.

Abstract: Publisher Summary The innovation of chromosome banding methods has affected the entire field of cytogenetic tumor research. Interest has been focused upon technically comparatively easy materials such as neoplastic hematological diseases, malignant exudates, and cell lines. Keeping in mind the fact that available data have been biased because of technical shortcomings, there exist several types or groups of neoplasms or neoplastic conditions that have been investigated to such an extent as to enable interpretations and assessments. The disorders chosen for this purpose are meningiomas and some myeloproliferative and lymphoproliferative diseases. In several disorders, the gonosomes comprise the chromosome types, which are possibly also involved in the nonrandom superimposed deviations. This is of interest because studies of the occurrence of Barr bodies and Y-bodies in tumor cells of mammary carcinomas, bladder carcinomas, and lung carcinomas and a variety of other neoplasms have indicated a fairly common loss of sex chromosomes in these cases. The reasons for this possible common loss of sex chromosomes in various neoplasms are at the current time completely obscure.

Nucleolus organizers in Mus musculus subspecies and in the RAG mouse cell line.

Abstract: Silver staining has been used to detect active nucleolus organizer regions (NOR's). By this criterion six mouse chromosomes, numbers 12, 15, 16, 17, 18 and 19, can have an NOR. The number and distribution of chromosomes with NOR's vary among inbred strains of Mus musculus musculus (C57BL/6J, BALB/cJ, C3H/HeJ and C3H/StCpr1BR) and in M. musculus molossinus. In a musculus X molassinus F1 hybrid, nucleolus organizers from each parent are silver stained.--Chromosomes which have NOR's in diploid cells also show them in tetraploid cells and in established cell lines. The BALB/cJ strain shows Ag-staining of NOR's on chromosomes 12, 15, 18 and occasionally 16. In the RAG cell line, which was derived from BALB/c, active NOR's are seen on 12, 15 and 18, even after these chromosomes have undergone structural rearrangements in the cell line. Some correlation exists between the amount of Ag-stain and the size of a secondary construction region, with a large amount of Ag-stain present on a chromosome which has a prominent secondary constriction. There is no correlation between the amount of Ag-stain and the presence or absence of C-band material.

Karyotype peculiarities of malignant lymphomas.

Abstract: Karyotypes of 30 malignant lymphomas were studied with the aid of G-banding. Frequent occurrence of rearranged chromosomes 14 and 11 was noted. In several tumors, identical acrocentric markers, appearing after translocation of the long arm of chromosome 11 on the long arm of chromosome 14, were revealed. Other common karyotype abnormalities in lymphomas were trisomy 3 and trisomy 18. The chromosomes preferentially involved in karyotype abnormalities of the malignant lymphomas are mostly not altered in other hemoblastoses.

Chromosome mapping of the genes that control differentiation and malignancy in myeloid leukemic cells

Abstract: The chromosome banding pattern has been analyzed in clones of mouse myeloid leukemic cells that differ in their ability to be induced to differentiate by the protein inducer MGI (macrophage and granulocyte inducer). None of the clones had a completely normal diploid banding pattern. The clones studied were either MGI+ (that can be induced to form Fc and C3 rosettes), a stage in the differentiation of myeloid cells, or MGI- (that cannot be induced to form these rosettes). All six cultured clones of MGI- cells from myeloid leukemias independently produced in six separate animals showed a loss of a piece of one chromosome 2 and this abnormal chromosome was maintained in leukemias derived from the cultured cells. This loss was not found in MGI+ clones or lymphoid leukemias. Five MGI+ mutants, derived from an MGI- clone with a loss of a piece of one chromosome 2, one normal chromosome 12, and two translocated chromosomes 12, maintained the abnormal chromosome 2 but lost either the one normal or one of these translocated chromosome 12. These results indicate that chromosomes 2 and 12 carry genes that control the differentiation of myeloid leukemic cells and that inducibility by MGI is controlled by the balance between these genes. We suggest that these chromosomes also carry genes that control the malignancy of these cells.

Microsurgically produced homozygous-diploid uniparental mice

Abstract: Shortly after fertilization, either the male or the female pronucleus was microsurgically removed from 202 F1 hybrid eggs derived from crosses of two inbred strains. Subsequent incubation of these haploid eggs in medium containing cytochalasin B, which inhibits cytokinesis but not nuclear division, enabled the remaining pronucleus to become diploid. After nuclear diploidization and transfer to regular culture medium, cleavage commenced normally, and a total of 135 successfully manipulated eggs continued in development and yielded 93 morulae and blastocysts. These embryos were surgically transferred to the uteri of pseudopregnant foster mothers who gave birth to seven live female offspring. Five of the females were derived from the maternal genome (gynogenesis) and the remaining two mice inherited only the paternal genes (androgenesis), depending on whether the female or male pronucleus had been retained in the egg, respectively. Homozygosity for a number of genetic loci positioned on different chromosomes and effecting the coat color phenotype and strain-specific allelic variants of several enzymes, urinary and plasma proteins, and hemoglobins could be demonstrated unequivocally in all instances. Chromosomal analysis revealed a normal diploid karyotype including two X chromosomes. Thus far, six of the seven homozygous-diploid (isogeneic) females have proved to be fertile and have given birth to progeny corresponding only to the pronuclear genotype of the mother.

Suppression of production of mouse 28S ribosomal RNA in mouse-human hybrids segregating mouse chromosomes

Abstract: Mouse-human somatic cell hybrids that lose (segregate) human chromosomes produce only mouse 28S ribosomal RNA even when they retain copies of the human chromosomes that contain the genes for 28S ribosomal RNA. In contrast, mouse-human hybrid cells that segregate mouse chromosomes produce only human 28S ribosomal RNA even when they have retained copies of mouse chromosomes that contain the 28S ribosomal RNA genes.

Serological evidence for H-Y antigen in Sxr, XX sex-reversed phenotypic males

Abstract: IT is generally considered that the Y chromosome is necessary for the development of the mammalian testis and the consequent male phenotype. Exceptions occasionally occur in man and other animals, where a male phenotype is associated with an apparently normal female karyotype. In some instances it has been possible to show that such “sex reversal” has an autosomal genetic basis. Although this might imply that the Y chromosome is not a prerequisite of maleness, it has not been excluded that a small male-determining region of the Y may have been translocated to an autosome without producing a recognisable karyotypic change1 (reviewed in ref. 2). The best studied case of male development with an apparently female karyotype is provided by the Sxr mutant in the mouse. This autosomal dominant condition causes both XX and XO mice to develop as males, although germ cells are absent in Sxr,XX animals and spermatogenesis is impaired in Sxr,XO mice. Sxr,XY males have a slightly reduced testis size but are usually fertile. Cytological scrutiny of mitotic and meiotic chromosomes (including chromosome banding) has revealed no evidence for a Y–autosome translocation, although a small translocation undetectable by the methods used cannot be ruled out (reviewed in ref. 2). This situation can now be investigated using serological methods for detecting H–Y (histocompatibility–Y) antigen on the surface of mouse sperm3 and male epidermal cells4. These techniques have provided further evidence that expression of this antigen is governed by a gene (or genes) on the Y chromosome even in the absence of the normal male phenotype5. Thus, serological demonstration of H–Y antigen offers a non-karyological criterion for the presence of a translocated portion of the Y in Sxr,XX males, because their cells should express H–Y if Sxr is a translocation involving the H–Y genetic determinant. We report here that Sxr,XX males express H–Y to a degree that may be the same or slightly lower than that of normal males, and that their Sxr,XY siblings seem to have near-normal levels of H–Y. The simplest explanation is that male-determining and H–Y-determining portions of the Y chromosome are present in the animals carrying Sxr.

N banded karyotypes of wheat species

Abstract: Nine of the twenty-one chromosome pairs of the hexaploid wheat Triticum aestivum var. Chinese Spring (genome constitution AABBDD) show distinctive N-banding patterns. These nine chromosomes are 4A, 7A and all of the B genome chromosomes. The remaining chromosomes show either faint bands or no bands at all. Tetraploid wheat, T. dicoccoides (AABB), showed banded chromosomes similar to those observed in the hexaploid. Of the diploid species T. monococcum, T. boeoticum, T. urartu and Aegilops sauarrosa showed little or no banding as would be expected of donors of the A and D genomes. Ae. speltoides had a number of N-banded chromosomes as would be expected of a candidate for the B genome donor. Since N-bands are not evident on some nucleolar organiser chromosomes, the staining specificity cannot be correlated with the presence of nucleolar organiser regions.

Replication pattern of the X chromosomes in three X/autosomal translocations.

Abstract: Three X/autosomal translocations, two familial and one de novo, were analyzed. Late-replicating chromosomes and chromosome regions were studied with R-banding techniques after BrdU incorporation. The first translocation, t(X;4)(q21;q13), was a de novo translocation, found in a woman with amenorrhea. The structurally normal X was late replicating in all cells. The second translocation, t(X;6)(p21;q26), was found in an unbalanced form, 46,XX,der(6), in a phenotypically abnormal girl; her mother carried the balanced translocation. In the mother's blood culture inactivation of the X's followed two modes: In 85% of the cells the normal X was late replicating, and in the remaining 15% the der(X) was inactivated, including the attached fragment of chromosome 6. The third translocation, t(X;17)(p11;q24), was found in three generations. In the phenotypically normal mother, who carried the balanced translocation, the late-replicating X was always the normal X. In her daughters, who had an unbalanced karyotype, 46,X,der(X), and multiple congenital abnormalities, the X part of the translocation chromosome was always late replicating. No spreading of inactivation over the attached autosomal region was observed, resulting for these patients in a partial trisomy of 17q. Their peculiar phenotype is described.

Chromosomes and causation of human cancer and leukemia. XXII. Karyotypic changes in malignant melanoma

Abstract: Detailed karyotypic analysis with G- and C-banding has been performed on cells of four malignant melanomas. The modal number in two cases was in the hypodiploid range, the chromosome numbers varying from 39 to 43. These two tumors had 5 to 13 marker chromosomes. The other two tumors were in the polyploid range, with modal numbers of 63 to 157 chromosomes. The cells had a minimum of 11 and a maximum of 40 marker chromosomes. Chromosome no. 1 was more frequently involved in aberrations than any other chromosome. The most common breakpoints on this chromosome were 1q21, 1q25 and 1q32. Frequent breakpoints were also noticed in the centromeric region in various chromosomes. In chromosome no. 1, however, the centromeric area does not seem to be involved. The more common breakpoints on the various chromosomes were 1q21, 1q25, 1q32, 5p13, 9q13, 11q23, 12q13. No common markers were noticed among these four cases of melanoma, but are noticed in unrelated tumors.

A cell line from an anaplastic transitional cell carcinoma of human urinary bladder.

Abstract: A cell line, TCCSUP, derived from an undifferentiated, Grade IV transitional cell carcinoma is described. The karyotype showed an abnormal distribution of chromosomes, with no obvious modal number. Distinct marker chromosomes were observed in both early and late in vitro passages. These cells have been subcultured over 50 times during a 20-month period. TCCSUP differs in certain morphological and immunological features from other cell lines from transitional cell carcinomas.

Possible localization of Gc-System on chromosome 4. Loss of long arm 4 material associated with father-child incompatibility within the Gc-System.

Abstract: A mentally retarded girl with a sporadically occurring B/F translocation was reexamined with new banding techniques. Chromosome material from the long arm of chromosome 4 was inserted into the long arm of chromosome 20. The segment 4q11 leads to q13 was lost. The formerly reported abnormal segregation of the Gc-system was verified. The localization of the Gc-locus on the lost segment cannot be ruled out.

Patterns of silver staining of human chromosomes

Abstract: The chromosomes of twenty individuals with normal karyotypes were studied to determine the patterns of staining with the Ag-AS technique. These patterns were shown to be variable from one individual to another, but characteristic and constant within each individual. In addition, one patient with chronic lymphocytic leukemia was studied, and shown to have an Ag-AS staining pattern that was distinctly different from that of normal subjects.

Pericentric inversion of chromosome 14 and the risk of partial duplication of 14q (14q31 leads to 14qter).

Abstract: Cytogenetic analysis after conventional staining and Q-banding demonstrated a pericentric inversion of chromosome 14 in the mother of a child with a mental retardation/multiple congenital abnormality syndrome and an abnormal chromosome 14. The proposita's partial duplication for the distal segment of 14q is apprently the result of crossing over within the inverted segment during meiosis. An attempt is made at assessing the risk that a carrier of the described pericentric inversion faces of having an abnormal child. The estimate of the risk depends on two factors: 1) the probability of a crossover occurring within the inverted segment during meiosis, and 2) the probability of a child with either of the two possible unbalanced recombinant chromosomes being born alive. An explanation is offered as to why some pericentric inversions confer a signifcant risk while others are so benign and occur with such a high frequency that they can be considered normal chromosomal variants, rather than chromosome aberrations.

Racial differences in the frequency of Q and C chromosomal heteromorphisms.

Abstract: THE biological and clinical implications of human chromosome heteromorphisms are poorly understood. These heteromorphisms are limited to certain groups, and are heritable1. Consistent variability between people, in both size and staining properties, is observed. This may reflect either structural or biochemical variations. Before chromosome banding procedures, the length of the Y was known to vary from person to person and from one ethnic group to another2. Some autosomal regions were also found to differ in various racial groups3,4. Using Q- and C-banding procedures, we have regions scored were (1) on the long arms (qh) of chromosomes 1,9 and 16; (2) on the short arms (P) of the acrocentric autosomes (13–15 and 21–22); and (3) on the centromere (c) of all other chromosomes. The results indicate significant differences between the samples of black and white children.

Stable association of the human transgenome and host murine chromosomes demonstrated with trispecific microcell hybrids

Abstract: Trispecific microcell hybrids were prepared by transferring limited numbers of chromosomes from a human/mouse gene-transfer cell line to a Chinese hamster recipient line. The donor cells employed were murine L-cells that stably expressed the human form of the enzyme hypoxanthine phosphoribosyltransferase. Karyotypic, zymographic, and back-selection tests of the resulting human/mouse/Chinese hamster microcell hybrids provided strong genetic evidence for a stable association of the human transgenome with host murine chromosomes in stable gene-transfer cell lines. This association, which may represent physical integration of the transgenome into the host cell genome, occurred at multiple chromosomal sites.

Evidence suggesting the existence of two H-Y antigens in the mouse

Abstract: An exceptional (C57BL/6 × BALB/c)F1 male mouse, from an X-irradiated father, and lacking the H-Y (“male”) antigen, on the basis of skin-graft testing, was found. Conventional serological tests for H-Y antigen, however, were positive. His karyotype contained only 39 chromosomes, the Y chromosome apparently being absent. Although the testes were small, lacked germ cells, and were essentially Leydig cell tumors, the mutant was normal with respect to external male phenotype, accessory glands, and sexual behavior. The data suggest that the histogenic and serological tests for H-Y antigen may detect two different antigens, paralleling findings with mutants of theH-2 complex, where histoincompatibility can be generated without accompanying serological changes.

Chromosomal polymorphisms of constitutive heterochromatin and inversions in Drosophila.

Abstract: A simple technique for preparing mitotic metaphases from a larval ganglion of Drosophila is described. Parallel examination of polytene and metaphase chromosome groups shows that inversion polymorphism in chromosome 3 of D. recticilia from East Maui (Hawaii) manifests a one-to-one correlation with a metaphase karyotype polymorphism due to the presence of an extra heterochromatic portion. These observations are consistent with the previous findings on other species of Hawaiian Drosophila. They strongly support the hypothesis that when one breakpoint of a long inverted segment of a chromosome element occurs in the vicinity of the constitutive heterochromatin, it may exert an effect in eliciting the production of heterochromatic material in the same chromosome.

Chromosomes and Causation of Human Cancer and Leukemia. XX. Banding Patterns of Primary Tumors

Abstract: Banding techniques were used in the study of the chromosomes of primary tumors from 16 patients with various types of cancer. The initial analysis with conventional Giemsa staining revealed chromosome abnormalities in 13 of the 16 tumors. Eleven of these 13 tumors and 2 of the 3 with normal karyotypes were reexamined with Q-, G-, and C-banding techniques: The 2 tumors were conventionally stained normal karyotypes were found to have no abnormalities. Nine of the tumors wre characterized by numerical changes only and 4 by both numerical and structural abnormalities. In 11 tumors, excessive chromosomes, identified with banding techniques, were usually found in the following groups (number of tumors involved is shown in parentheses): No. 5 (5), No. 8 (6), No. 11 (5), no. 13 (5), and No. 21 (5). The primary tumors examined had hyperdiploid modes; only 4 of these tumors contained marker chromosomes, as opposed to the high frequency of markers in metastatic cancer cells and the presence, usually, of high polidy (near-triploidy or near-tetraploidy). The data suggested that the karyotypic changes in primary cancers consist primarily of numerical changes (hyperploidy), rather infrequent appearance of marker chromosomes, and, when present, only 1 or 2 markers.

The origin and behavior of two isodicentric bisatellited chromosomes.

Abstract: Karyotyping revealed three cell lines in a boy with mental retardation and few other abnormalities. Thirty cells exhibited a normal karyotype, and 54 had an extra acrocentric chromosome of E group size with satellites on the long and short arms. The remaining 20 cells each had, in addition to the first marker (M1), a second tiny bisatellited chromosome (M2). C-banding demonstrated that both markers were dicentric. G-, C-, and Q-banding and satellite association data were consistent with the markers having originated from chromosome 15 material. We propose that M1 was formed from a meiotic breakage and a chromatid fusion in the proximal long arms of an acrocentric pair. This would have produced a symmetrical isodicentric chromosomes, plus one or two acentric fragments. M2 then could have resulted from a dicentric bridge-break-synthesis-reunion phenomenon. This model of abnormal meiotic exchange can be generalized to encompass the formation of other dicentric isochromosome cases of isochromosome X.

Assignment of the integration site for simian virus 40 to chromosome 17 in GM54VA, a human cell line transformed by simian virus 40.

Abstract: GM54VA human cells transformed by simian virus 40 (SV40) were fused with peritoneal macrophages obtained from three different mouse strains. All 27 hybrid clones studied were positive for SV40 tumor antigen in 100% of their cells and contained human chromosome 17. Human chromosome 17 was the only human chromosome present in five of the hybrid clones. Fusion of GM54VA cells and either thymidine kinase (EC 2.7.1.75)-deficient mouse or Chinese hamster fibroblasts resulted in the growth in hypoxanthine-aminopterin-thymidine medium of hybrid clones positive and negative for SV40 tumor antigen. Counterselection of the hybrid clones positive for tumor antigen in medium containing 5-bromodeoxyuridine resulted in the growth of hybrid cells that were negative for tumor antigen. These experiments indicate that negative for tumor antigen. These experiments indicate that SV40 is integrated in only one of the two parental human chromosomes 17. Because the genome of SV40 has been assigned to human chromosome 7 in two other SV40-transformed human cell lines, at least two different integration sites for SV40 would seem to be present in human cells: one located in human chromosome 7 and the other located in human chromosome 17.