Showing papers on "Chromosome published in 1975"

Somatic rearrangement of chromosome 14 in human lymphocytes.

Abstract: Ataxia-telangiectasia is a rare genetic disorder associated with immune deficiency, chromosome instability, and a predisposition to lymphoid malignancy. We have detected chromosomally anomalous clones of lymphocytes in eight patients with this disorder. Chromosome banding disclosed that the clones are consistently marked by structural rearrangement of the long arm (q) of chromosome 14. A translocation involving 14q was found in clones obtained from seven of the eight patients whereas a ring 14 chromosome was found in a clone obtained from the other. These findings as well as data obtained by others for patients with ataxia-telangiectasia suggest that structural rearrangement of 14q is the initial chromosomal change in lymphocyte clones of patients with this disorder. Chromosomes of lymphocytes from one of the patients were studied before and after the onset of chronic lymphocytic leukemia. Before leukemia was diagnosed, the patient had a lymphocyte clone with a 14q translocation. This clone appears to have given rise to the leukemic cells. We hypothesize that structural rearrangement of 14q is directly related to abnormal growth of lymphocytes and that it may be a step toward the development of lymphoid malignancies. Increasing evidence, provided by others, for the nonrandom involvement of 14q in African-type Burkitt's lymphoma and other lymphoid neoplasms further strengthens this hypothesis.

Is Fanconi's anaemia defective in a process essential to the repair of DNA cross links?

Abstract: FANCONI'S anaemia (FA) is a rare autosomal recessive disease of man, characterised by a progressive hypoplastic pancytopenia associated with diverse congenital anomalies1,2, spontaneous chromosome breakage3 and predisposition to leukaemia and other cancers4,5. Lymphocytes from FA patients were found to be excessively susceptible to chromosome breakage by di- or polyfunctional alkylating agents6,7, and this was interpreted as a possible indication of defective DNA repair of the FA cells7. Seeking evidence for this, I have tested lymphocytes from FA patients for their chromosome response to mono- and difunctional mitomycins in relation to the cell cycle phase at the time of treatment, and have found that FA cells have a specific defect in the repair of pre-aberration lesions induced by difunctional mitomycin; the lesions are possibly DNA cross links of the interstrand type. The rationale of this experiment was the knowledge that if damage to DNA is left unrepaired it can be linked causally to the formation of chromosome aberrations by a process that resides in semi conservative DNA replication8–12. Since the repair of DNA damage is a rate-limiting process, the treatment of repair-proficient cells in early G1 would leave more time for repair before the damage is fixed into chromosome aberrations during the S phase, and consequently would result in fewer chromosome aberrations than treatment during the transition from G1 to S. In the repair-deficient cells, however, DNA damage induced by treatment in any position of G1 would be linked maximally to the formation of chromosome aberrations.

Parasexual Approaches to the Genetics of Man

Abstract: SOMATIC CELL GENETIC METHODS Cell Hybridization SCG gene mapping depen�s on parasexual events in cultured somatic cells (1-4). These are cell hybridization (5, 6) and chromosome elimination (7, 8) (see section on chromosome elimination). In cell hybridization (Figure I) cells are fused to form heterokaryons, with nuclei of both types within a single cytoplasm. The heterokaryons may be used for genetic complementation studies (see section on genetic complementation). If the nuclei fuse and the resulting synkaryon divides and proliferates. a hybrid cell population is formed. The human parental cells are normal diploid cells, usually fibrocytes from skin biopsy or leucocytes from peripheral blood. It is important that they possess a well-characterized karyotype and genetic constitution. The nonhuman cells are usually tissue culture-adapted heteroploid rodent cells. The parental cells are mixed together either as substrate (9) or suspension (10) cultures. It may be important to adjust the density and/or ratio of one parental cell type to the other (9, 10) to maximize yield of heterokaryons. Heterokaryons form spontaneously, but only at a low frequency. which de­ pends principally on the cell lines employed. Agents can be added to the parental cell mixtures in order to increase the frequency of heterokaryon formation. The agent most successfully employed is the parainfluenza virus designated

Chromosome measurement and sorting by flow systems.

Abstract: A flow microfluorometer was used to measure metaphase chromosomes in suspension at rates up to 100,000 per min. Chromosomes from cells of the Chinese hamster M3-1 cell line were isolated, stained for DNA with the fluorescent dye ethidium bromide, and analyzed for DNA content. Nine distinct peaks were resolved that correspond well with independent chromosomal DNA measurements made with a high-resolution scanning cytophotometer. Chromosomes were sorted from each peak by an electronic cell sorter. Visual examination of each fraction indicated the purity of the sorted chromosomes. This novel technology allows separation of purified populations of individual chromosomes suitable for biochemical and biological characterizations.

B-Chromosome Systems in Flowering Plants and Animal Species

Abstract: Publisher Summary This chapter discusses the B-chromosome systems in flowering plants and animal species. The term B chromosome is introduced to describe extra chromosome which have little if any effect on visible characters of the plant, which are not homologous with the A chromosomes of the normal complement, and which are extremely irregular in their meiotic distribution. B Chromosomes are now known under a variety of different names, including supernumerary and accessory, which are the most common alternatives. B chromosomes are dispensable and nonhomologous with A chromosomes. These two characteristics above all others most sharply differentiate them from members of the basic A-chromosome complement. The distribution of B chromosome in plant and animal species is discussed. In many plants and animals the B chromosomes are completely stable during the cell cycle and are inherited in a constant and unchanging form along with the A chromosomes. Some plant species have an apparent order in their instability, which results in exclusion and/or accumulation of B chromosomes in specific tissues and organs. The significance of B-chromosome effects in flowering plants and animals is discussed.

The possibility of latent centromeres and a proposed nomenclature system for total chromosome and whole arm translocations

Abstract: Translocations involving entire chromosomes or whole chromosome arms may not necessarily require deletion of a centromere. Conceivably, in the process of centromeric or telomeric fusion or of fusion of a centromere with a telomere, centromeric inactivation may occur, thus preserving both centromeres—one functional, the other latent—in the resultant translocation chromosome. If such latent centromeres exist and, in addition, are capable of being reactivated, it would explain how additional functional centromeres are acquired in the reverse process of chromosomal fission or fragmentation. A system of nomenclature is proposed for identifying the origin and nature of these chromosomal rearrangements.

Chromosome polymorphism in a human newborn population. II. Potentials of polymorphic chromosome variants for characterizing the idiogram of an individual.

Abstract: Replicate chromosome preparations of umbilical-cord-blood leukocytes from 376 neonates born at the Albert Einstein College Hospital, Bronx, New York, were stained with C-, Q-, and G-banding methods to determine the frequencies and distributions of the variable chromosome bands. The C-band variants of primarily chromosomes 1, 9, and 16, as well as those of the remaining C, E, and F-group chromosomes, and the brightly fluorescing Q-band variants of chromosomes 3 and 4 and all of the acrocentrics, including the Y, were similarly analyzed. Polymorphism of these chromosome regions was so extensive that the idiogram of each of the 376 newborns of this study had a unique variant pattern, even when only the C- or only the Q-band patterns were compared. The distribution of polymorphic Q-bands in the population sampled was consistent with the expectations of the Hardy-Weinberg law, with the exception of chromosomes 3 and 22, where some deficiency of individuals with "homozygous" Q-band patterns was found. The baseline data presented here reinforce the view that polymorphic chromosome characteristics are very useful markers for characterizing the karyotype of an individual, for pedigree studies, for prenatal chromosome analyses, for population studies, for attempts at gene localizations, and for identifying specific cells or their chromosomes in somatic cell genetic studies.

New chromosomal syndromes.

Abstract: The field of human cytogenetics has changed considerably since 1891 when Hansemann studied chromosomes in human cells and attempted to assign a chromosome number to them. 1 The first important discovery was made in 1949 by Barr and Bertram when they observed the sex chromatin body, a small, darkly staining chromatin mass present in the interphase nuclei of females 2 (Fig 1, left). This discovery later made possible the presumptive diagnosis of Turner and Klinefelter syndromes by the simple analysis of a buccal smear. After 1956, when Tjio and Levan together developed a simple technique that made possible the study of human chromosomes, 3 the field progressed rapidly. During the ensuing five years, the causes of trisomy 13, 18, and 21 syndromes; Turner syndrome, and Klinefelter syndrome were established. The next five years saw the application of autoradiography for better identification of chromosomes and the delineation of more subtle chromosome

Late replicating bands of human chromosomes demonstrated by fluorochrome and Giemsa staining.

Abstract: The addition of thymidine (TdR) to cells growing in a medium containing 5-bromodeoxyuridine (BUdR) at the end of the first replication cycle results in the incorporation of TdR into the late replicating DNA regions. These sites can be visualized by staining the metaphase chromosomes with the fluorescent dye “33 258 Hoechst” or a “33 258 Hoechst” Giemsa procedure. A sequence of late replication patterns has been established in metaphase chromosomes of cultured human peripheral lymphocytes. The patterns are in agreement with those obtained by the standard autoradiographic procedures, but are more accurate. As is known from autoradiography, late replicating bands are in the position of G or Q bands. The “33 258 Hoechst” Giemsa staining procedure of chromosomes which have replicated in the presence of BUdR first and in TdR for the last 2 hrs of the S phase is preferable to the currently used Giemsa banding techniques: the method yields very well banded metaphases in all preparations examined, as the chromosome structure is not disrupted by the pretreatment. The bands are very distinct, even in the “difficult” chromosomes (e.g No. 4, 5, 8, and X). In female cells the late replicating X chromosome can be identified by its size and staining pattern. In addition to the replication asynchrony, the sequence of replication within both X chromosomes in female cells is not absolutely identical. The phenomenon of a phase difference in replication between the homologues is not a peculiarity of the X chromosome, but can be found in all autosomes as well as in homologous positions on the chromatids of individual chromosomes.

Distribution of sister chromatid exchanges in the euchromatin and heterochromatin of the Indian muntjac.

Abstract: The frequency of sister chromatid exchanges (SCEs) was determined for the chromosomes (except Y2) of the Indian muntjac stained by the fluorescence plus Giemsa (FPG) or harlequin chromosome technique. The relative DNA content of each of the chromosomes was also measured by scanning cytophotometry. After growth in bromodeoxyuridine (BrdU) for two DNA replication cycles, SCEs were distributed according to the Poisson formula in each of the chromosomes. The frequency of SCE in each of the chromosomes was directly proportional to DNA content. A more detailed analysis of SCEs was performed for the three morphologically distinguishable regions of the X-autosome composite chromosome. The SCE frequency in the euchromatic long arm and short arm were proportional to the amount of DNA. In contrast, the constitutive heterochromatin in the neck of this chromosome contained far fewer SCEs than expected on the basis of the amount of DNA in this region. A high frequency of SCE, however, was observed at the point junctions between the euchromatin and heterochromatin.

Non-random occurrence of 7-14 translocations in human lymphocyte cultures

Abstract: SOMATIC cells dividing in vitro occasionally show chromosome recombination between non-homologues most often in situations associated with an increased frequency of chromosome breakage and reunion1,2 their occurrence being recognised by the observation of exchange figures. With the advent of new techniques for chromosome identification3 it is now possible to identify the chromosomes involved in these rearrangements and to recognise some translocations which might otherwise be missed.

Premature centromere division: A mechanism of non-disjunction causing X chromosome aneuploidy in somatic cells of man

Abstract: Apparent acentric fragments which replaced a C-group chromosome in cultured blood lymphocytes from a woman patient were shown by autoradiography, G-banding and C-banding to be complete X chromosomes in which the centromere had divided prematurely in relation to the centromeres of other chromosomes in the same metaphase. Metaphases with multiple 'fragments' suggested that non-disjunction of the 'fragments' had occurred. This anomaly of the X chromosome was associated with increased aneuploidy of a C-group chromosome, presumed to be X. Premature centromere division of the X chromosome (PCD, X) appeared to be a mechanism of non-disjunction which caused significant monosomy and trisomy of the X chromosome in blood cells and skin fibroblasts. The frequency of cells with multiple fragments and the extent of the aneuploidy in 48 hr. blood cultures indicated that this mechanism of non-disjunction operated during mitosis both in vivo and in vitro. Premature centromere division occurred at a lower frequency in normal women donors, and was age-related, being four times more frequent in women 60 years and older than in women under 40. Associated with the higher frequency of PCD, the older women also showed evidence of increased X chromosome aneuploidy. Premature centromere division of the X chromosome is considered to be the mechanism of non-disjunction, causing the well-documented increased number of 45, -C metaphases in ageing women. Premature centromere division was rare in men, but an age effect was again suggested.

The Giemsa-staining centromeres of Nigella damascena

Abstract: The centromere regions of each chromosome in the complement of Nigella damascena (2n equals 2x equals 12) stain differentially with Giemsa at interphase and throughout all the principal stages of mitosis and meiosis. Each centromere is seen to consist of a pair of sister half-centromeres which appear as 2 differentially stained dots. The appearance and behaviour of these dots indicates that they are kinetochores. The technique used does not stain centromeres in other plant species investigated, a fact which shows that the centromeres of Nigella are in some way different. The implications of this observation in relation to centromere polymorphism are discussed.

Attraction between centric heterochromatin of human chromosomes.

Abstract: An analysis of the pattern of association of acrocentric chromosomes with nonacrocentric chromosomes in human lymphocyte metaphases was performed. This pattern in nonrandom with respect to chromosome length and intrachromosomal distribution. There is a general preference for the centric regions, most pronounced at the proximal segments of the long arms of chromosomes 1, 9, and 16, which is interpreted to reflect heterochromatin attraction during interphase. Comparison of the association patterns of homologous chromosome 1's differing with regard to the size of their heterochromatic regions corroborates this interpretation. The possible significance of heterochromatin attraction for the formation of spontaneous and induced chromosome anomalies is discused.

Genetic Control of Chromosome Elimination during Haploid Formation in Barley.

Abstract: Genetic control over chromosome stability in the interspecific hybrid embryos of Hordeum vulgare and H. bulbosum has been hypothesized to reside on specific chromosomes. In this study, crosses between the primary trisomic lines for the seven different H. vulgare chromosomes and tetraploid H. bulbosum revealed that both chromosomes 2 and 3 of H. vulgare were involved in the control of chromosome elimination. Subsequent crosses using the available monotelotrisomics for chromosomes 2 and 3 led to the conclusion that both arms of chromosome 2 and the short arm of chromosome 3 most likely contain major genetic factors.—From the results of this study and the genome balance observed in the interspecific crosses between H. vulgare and H. bulbosum at the diploid and tetraploid cytotypes, it appears that the factors causing the elimination of the bulbosum chromosomes are located on the H. vulgare chromosome. These factors are offset or balanced by factors on the H. bulbosum chromosomes which, when present in sufficient dosage, either neutralize the effects of the vulgare factors or are able to "protect" the bulbosum chromosomes.

Chromosome abnormalities as a cause of infertility in mares.

Abstract: Chromosomal abnormalities have been detected in seven mares isolated by their poor reproductive performance. All had small or rudimentary gonads and absent or irregular oestrous cycles. Two mares had an XO genotype, one was a 65,XXX female and another a 64,XY sex-reversed female. Two other mares were sex chromosome mosaics of the 63,X/64,XX type. The seventh mare showed a normal female karyotype but a small extra autosomal fragment was found in a few cells.

5-Methylcytosine in Heterochromatic Regions of Chromosomes: Chimpanzee and Gorilla Compared to the Human

Abstract: Fixed metaphase chromosomes of gorilla and chimpanzee were UV-irradiated to produce regions of single-stranded DNA and then treated with antibodies specific for the minor DNA base 5-methylcytosine (5 MeC). An indirect immunofluorescence technique was used to visualize sites of antibody binding. In the gorilla six pairs of autosomes contained major fluorescent regions, indicating localized regions of highly methylated DNA. These corresponded, with the exception of chromosome 19, to the major regions of constitutive heterochromatin as seen by C-banding. The Y chromosome also contained a highly fluorescent region which was located just proximal to the intense Q-band region. In the chimpanzee no comparable concentrations of highly methylated DNA were seen. Smaller regions of intense 5 MeC binding were present on perhaps six chimpanzee chromosomes, including the Y. Five of these corresponded to chromosomes which were highly methylated in the gorilla.--There is diversity among the human, gorilla and chimpanzee in both the size and location of concentrations of 5 MeC, supporting the idea that satellite DNA evolves more rapidly than DNA in the remainder of the chromosome.

Chromosome banding pattern conservatism in birds and nonhomology of chromosome banding patterns between birds, turtles, snakes and amphibians.

Abstract: The G-banded karyotypes of 4 species of birds representing the orders Galliformes, Columbiformes and Musophagiformes were compared. Banding pattern homology between orders was limited to 5 major chromosome arms and the Z chromosome. Even in these major chromosome arms pericentric and paracentric inversions produced alteration of the banding pattern sequences. Addition of constitutive heterochromatin was responsible for changes in banding pattern in the Z chromosome. The chromosome banding patterns of an emydid turtle, Terrepene Carolina, 5 species of boid snakes of the genera Liasis, Acrantophis, and Sanzinia and the African clawed-frog, Xenopus muelleri, were also compared to the bird chromosome banding patterns. No homology was observed between any of these major groups: bird, snake, turtle, amphibian. However, intergrouphomology was apparent. — The data obtained do not support reports of broad interordinal direct homology of the macrochromosomes of birds and refutes the idea of a primitive bird karyotype with 3 pairs of “A group” chromosomes and 3 pairs of “B group” chromosomes. — The major mechanisms responsible for chromosome evolution in birds appear to be centric and tandem fusions, paracentric and pericentric inversions, and addition or deletion of heterochromatin.

Chromosomal evolution in the lizard genus Varanus (reptilia).

Abstract: The karyotypes have been determined of 16 of the 32 species of the genus Varanus, including animals from Africa, Israel, Malaya and Australia. A constant chromosome number of 2n = 40 was observed. The karyotype is divided into eight pairs of large chromosomes and 12 pairs of microchromosomes. A series of chromosomal rearrangements have become established in both size groups of the karyotype and are restricted to centromere shifts, probably caused by pericentric inversion. Species could be placed in one of six distinct karyotype groups which are differentiated by these rearrangements and whose grouping does not always correspond with the current taxonomy. An unusual sex chromosome system of the ZZjZW type was present in a number of the species examined.

Cytoplasm-chromosome interactions in Drosophila melanogaster

Abstract: INSTANCES of exceptionally high frequencies of mutation1, male recombination2, chromosomal aberration3 and sterility4 have been observed, often simultaneously5–8, in many natural populations of Drosophila melanogaster during the past thirty years. In some cases2,6,8, these exceptional phenomena seem to be associated with chromosomes but not necessarily with specific loci. Tests for an infectious agent have given negative results2,4. Cytoplasmic factors, interacting with specific chromosomes, have been implicated in a few cases4,7 but in many others the experimental design did not provide for their detection. We report large differences in male recombination and F1 sterility between reciprocal crosses of strains derived from temporally and geographically diverse natural populations and several commonly-used laboratory marker and balancer stocks. Cytoplasm–chromosome interactions are suggested.

Lateral asymmetry in human constitutive heterochromatin.

Abstract: Human lymphocytes were grown for one replication cycle in BrdU, stained with 33258 Hoechst, exposed to UV light and subsequently treated with 2 x SSC and stained with Giemsa. This technique differentially stains the constitutive heterochromatin of chromosomes 1, 9, 15, 16, and the Y. In the heterochromatin of chromosome 9 both sister chromatids stained darkly and symmetrically but in the other four chromosomes the heterochromatin showed lateral asymmetry, one chromatid being darkly stained while its sister chromatid was as pale or paler than the rest of the chromosome. The lateral asymmetry is presumed to reflect an underlying asymmetry in distribution of thymine between the two strands of the DNA duplex in the satellite DNA component of the chromosomes. In some number 1 chromosomes compound lateral asymmetry was seen; darkly staining material was present on both sister chromatids although at any given point lateral asymmetry was maintained so that if one chromatid stained darkly the corresponding point on the sister chromatid was very pale. The pattern of compound lateral asymmetry varied among the number 1 chromosomes studied but was constant for any one homologue from one individual. This technique reveals a previously unsuspected type of polymorphism within the constitutive heterochromatin of man.

Subunit structure of chromatin is the same in plants and animals

Abstract: ALTHOUGH plants and animals diverged from each other nearly 109 yr ago, the histone composition of their chromosomes is remarkably similar1; in particular, the arginine-rich histones III and IV of peas and cows differ by only four and two amino acids, respectively2,3. Such extreme evolutionary conservation of a protein sequence argues that histones are crucial to chromosome structure and/or function, and further suggests considerable similarity, at the molecular level, between the chromosomes of plants and animals. We present evidence here for such a similarity.

Detection of nonintegrated plasmid deoxyribonucleic acid in the folded chromosome of Escherichia coli: physiochemical approach to studying the unit of segregation.

Abstract: Physiocochemical evidence presented indicates plasmid deoxyribonucleic acid (DNA) can associate with host chromosome without linear insertion of the former into the latter. This conclusion is based on the observation that covalently closed circular (CCC) plasmid DNA can cosediment with undegraded host chromosome in a neutral sucrose gradient. When F plus bacteria are lysed under conditions that preserve chromosome, approximately 90% of CCC F sex factor plasmid (about 1% of the total DNA) is found in folded chromosomes sedimenting at rates between 1,500 and 4,000s. The remaining 10% of the CCC F DNA sediments at the rate (80S) indicative of the free CCC plasmid form. Reconstruction experiments in which 80S, CCC F DNA is added to F plus or F minus bacteria before cell lysis show that exogenous F DNA does not associate with folded chromosomes. In F plus bacteria, F plasmid is harbored at a level of one or two copies per chromosomal equivalent. In bacteria producing colicin E1, the genetic determinant of this colicin, the Col E1 plasmid, is harbored at levels of 10 to 13 copies per chromosomal equivalent; yet, greater than 90% of these plasmids do not cosediment with the 1,800S species of folded chromosome. However, preliminary evidence suggests one or two Col E1 plasmids may associate with the 1,800S folded chromosome. Based on evidence presented in this and other papers, we postulate F plasmid can link to folded chromosome because the physicochemical structure of the plasmid resembles a supercoiled region of the chromosome and, therefore, is able to interact with the ribonucleic acid that stabilizes the folded chromosome structure. Implications of this model for F plasmid replication and segregation are discussed.

Chromosome relationships between Lolium and Festuca (Gramineae)

Abstract: With a view to eclucidating chromosome relationships between Lolium perenne (Lp), L. multiflorum (Lm) and Festuca pratensis (Fp), chromosome pairing in different diploid (2n=14), auto-allotriploid (2n=3x=21), trispecific (2n=3x=21), amphidiploid (2n=4x=28) and auto-allohexaploid (2n=6x=42) hybrids between them was analysed. At all these levels of ploidy there was very good chiasmate pairing between the chromosomes of the three species and, on the whole, there was little evidence of preferential pairing of the chromosomes of a particular species in the triploid, tetraploid and hexaploid hybrids. A critical test for this also came from the synaptic ability of the chromosomes of the single genome with those of the duplicated genome in the auto-allotriploids which formed predominantly trivalents with 2, 3 or even 4 chiasmata. Moreover, the homology between the Lp and Lm chromosomes seems strong enough to pass the discrimination limits of the B-chromosomes which do not suppress homoeologous pairing in the Lp LmLm triploid and LpLm diploid hybrids. — The triploids having two genomes of a Lolium species and one of F. pratensis had some male and female fertility which suggested genetic compatibility of the parental chromosomes resulting, presumably, in compensation at the gametic level. Also, the occurrence of comparable chiasma frequencies in the auto-allotriploids and trispecific hybrids showed that they were not markedly affected whether two doses of one genome and one of the other or all the three different genomes from the three species were present. From the trend of chromosome pairing in all these hybrids it is concluded that there is little structural differentiation between the chromosomes of the three species, no effective isolation barrier to gene-flow between them, and that they are closely related phylogenetically, having possibly evolved from a common progenitor. Taxonomic revision of the two Lolium species is suggested.

Two complex translocations in chronic granulocytic leukemia involving chromosomes 22, 9, and a third chromosome

Abstract: Among 13 Ph-positive cases of chronic granulocytic leukemia (CGL), banding studies revealed two with complex rearrangements involving translocation of the long arm of number 22 to another autosome and a segment of that chromosome translocated to the long arm of number 9. In a patient with both CGL and sickle cell anemia, the 3-way rearrangement involved chromosomes 5, 9, and 22; and he also had a second Phildaelphia chromosome and two constitutional variants: pericentric inversion of the other number 9 chromosome and satellite polymorphism in the G group. The karyotype of the leukemic cells was interpreted as: 47,XY,inv(9) (p11q13),t(5;9;22)(q13;q34;q11)+del(22)(q11).

The mitotic chromosomes of Notophthalmus (=Triturus) viridescens: localization of C banding regions and DNA sequences complementary to 18S, 28S and 5S ribosomal RNA.

Abstract: The metaphase chromosomes of Notophthalmus (Triturus) viridescens have been studied by C-banding and in situ hybridization. The chromosomes show the pericentric C-banding seen in many organisms and in addition have interstitial C-bands located a short distance from the pericentric C-bands on each chromosome arm. A few C-bands are seen in telomeric regions. Regions which hybridize in situ with 18S and 28S ribosomal RNA were found on three chromosome pairs. The animals studied fell into three groups with respect to which of the six possible sites showed detectable hybridization with 18S and 28S RNA. Individual animals differed not only in the pattern of in situ hybridization of ribosomal RNA but also in the number of ribosomal RNA cistrons in the genome as measured by saturation hybridization on purified DNA. In situ hybridization showed five pairs of chromosomes which contained DNA complementary to 5S RNA. The four pairs of subtelocentric chromosomes in the N. viridescens karyotype all have 5S DNA in the pericentric regions. The fifth cluster of 5S DNA is in the middle of one arm of the chromosomes in one of the two smallest submetacentric pairs in the genome. The five sites of 5S DNA differ markedly in the level of in situ hybridization with 5S cRNA.