Showing papers on "Chromosome published in 1974"

The development of the macronucleus in the ciliated protozoan Stylonychia mytilus

Abstract: Ciliated protozoa are characterized by generative micronuclei and vegetative polyploid macronuclei. Micronuclei of Stylonychia mytilus contain 1 600 times as much DNA per haploid genome as E. coli. Most of this DNA is shown to be repetitive. The development of the macronucleus involves, as demonstrated by cytology, only 1/3 of the chromosomes which in a first replication phase are polytenized in probably 5 replication steps and appear as giant chromosomes. At this developmental stage considerable amounts of repetitive DNA are still present in the chromosomes. During the subsequent disintegration phase more than 90% of the DNA are eliminated from the macronucleus anlage. The remainder is further replicated five times and composes the final macronucleus. Since this DNA reassociates with a reaction rate almost identical to an ideal second order reaction its kinetic complexity can be determined by comparison with the kinetic complexity of E. coli DNA. Macronuclear DNA reassociates with a kinetic complexity of 26 times the kinetic complexity of E. coli DNA (corrected for GC content) which indicates that macronuclear DNA sequences exist at a ploidy level of 4 096 C. We assume that macronuclear DNA may be present only once per haploid genome. In this case it represents only 1.6% of the DNA in micronuclei or 10% of the DNA in the giant chromosome stage.

Location of the genes coding for 18S and 28S ribosomal RNA in the human genome

Abstract: 3H-rRNA obtained from Xenopus laevis tissue cultured cells, or a 3H-cRNA made from Xenopus ribosomal DNA, was used for heterologous in situ hybridisation with human lymphocyte metaphase chromosomes. Prior to hybridisation, chromosome spreads were stained with Quinacrine and selected cells showing good Q-banding photographed; the same cells were then rephotographed after autoradiography and pairs of photographs for each cell were used to make dual karyotypes. The chromosomes within each karyotype were divided into equal sized segments (approx. 0.7 μ), with a fixed number of segments for each chromosome type. The distribution of silver grains between segments showed that the 3H-RNAs hybridised specifically to the nucleolar organising regions of the D and G group chromosomes with no other sites of localised labelling in the complement. Control experiments showed no localisation, with insignificant labelling, when metaphase spreads were incubated in a mixture containing Xenopus3H-rRNA and competing cold human (HeLa) rRNA. Filter hybridisation experiments on isolated human DNA showed that the Xenopus derived 3H-RNAs hybridised to a fraction of human DNA which was on the heavy side of the main DNA peak and that these RNAs were competed out in the presence of excess cold human rRNA, confirming the specificity of the heterologous hybridisation. In situ hybridisation experiments were also carried out on cells from individuals with one chromosome pair showing heteromorphism for either a very long stalk (nucleolar constriction) subtending a satellite, or a large satellite. It was shown that the chromosome with the large stalk hybridised four times as much 3H-rRNA as its homologue, whereas differences in the sizes of the subtended satellites did not materially affect hybridisation levels indicating that rDNA is located in the stalks and not the satellites. The amount of 3H-rRNA hybridised differs between chromosomes and individuals; these differences are heritable and rDNA can be detected by in situ hybridisation in all three chromosomes number 21 in cells from Down's patients and in translocated chromosomes conta.ining a nucleolar constriction. Different D and G group chromosomes which hybridised equal amounts of 3H-rRNA participated in rosette associations at metaphase in a random fashion in some individuals and in a non-random fashion in others. In all individuals studied chromosomes with large amounts of rDNA were not found to be preferentially involved in association. It was therefore concluded that the probability of a chromosome being involved in the formation of a common nucleolus is not a simple function of its rDNA content and other possible factors are considered.

Origin of Nicotiana tabacum L. detected by polypeptide composition of Fraction I protein

Abstract: THERE is no well-authenticated record of the occurrence of Nicotiana tabacum, the commercial tobacco plant, in the wild state, and so its origin and evolution are of great interest. N. tabacum (n=24) is believed to have arisen by chromosome doubling after hybridisation of N. sylvestris Spegazzini and Comes (n = 12) with a species in the Tomentosae section of Nicotiana. Goodspeed and Clausen1 suggested that N. tomentosa Ruiz and Pavon (n = 12) was the species, but Clausen2 amended it to N. tomentosiformis Goodspeed (n = 12). Goodspeed3 favoured N. otophora Grisebach (n = 12), however, because of its present-day geographical distribution; N. otophora is found together with N. sylvestris in an area on the eastern slopes of the Andes whereas N. tomentosiformis occurs further north where N. sylvestris has not been found. Later evidence, however, suggests N. tomentosiformis as the more likely progenitor of N. tabacum. Gerstel4, from an analysis of the segregation of artificial polyploids of N. tabacum × N. tomentosiformis and N. tabacum × N. otophora, concluded that N. tomentosiformis showed the greater chromosome homology with N. tabacum, and Sheen5–7 from an analysis of isoenzyme patterns and sterol composition supported the conclusion that N. sylvestris and N. tomentosiformis were the likely progenitors of N. tabacum. From an analysis by isoelectric focusing of the polypeptide composition of Fraction I protein isolated from N. tabacum and the putative progenitor species, we now report that N. tabacum arose from the hybridisation of N. sylvestris ♀ × N. tomentosiformis ♂.

Premature chromosome condensation I. Visualization of X-ray-induced chromosome damage in interphase cells

Abstract: A new method is described to visualize chromosome damage in interphase cells immediately after exposure to mutagenic agents This method involves the fusion of treated interphase cells with untreated mitotic cells which results in the induction of premature chromosome condensation (PCC) Chinese hamster ovary (CHO) cells were treated with X-rays and chromosome aberrations were scored in G2-PCC and the mitotic chromosomes The incidence of aberrations was significantly higher in PCC than that observed in the mitotic chromosomes of the treated cells Post-irradiation incubation for I h before fusion allowed the repair of some of the chromosome damage Data are also presented which indicate that the extent of radiation damage visualized in PCC is inversely proportional to the degree of chromosome condensation These results indicate that the PCC method has a greater senstivity in the detection of induced chromosome damage than the standard method of scoring metaphase chromosomes

Effects of ethidium bromide on mitosis and chromosomes: a possible material basis for chromosome stickiness.

Abstract: When two types of mammalian cells were treated with ethidium bromide for several hours, the mitotic figures showed no chromatid breaks or exchanges but a high incidence of sticky chromosomes. Electron microscopic examinations revealed that many chromosomes are connected by submicroscopic chromatin strands of various widths. Chromosome stickiness, therefore, is interpreted as entanglement of chromatin fibers between unrelated chromosomes, probably caused by abnormal condensation behaviors prior to mitosis. Presumably, chromatin breaks would occur when sticky chromosomes separate during anaphase. Such microscopically undetectable breaks expressed as various kinds of chromosomal aberrations in the next mitosis when the damaged cells were permitted to recover in the absence of ethidium bromide.

Cytological evidence for holocentric chromosomes of the silkworms, Bombyx mori and B. mandarina, (Bombycidae, Lepidoptera)

Abstract: The nature of the centromere and the orientation in meiosis of silkworm chromosomes were investigated using the trivalent of the F1 hybrid between the wild and domestic silkworm and X-ray-induced aberrant chromosomes as well as normal silkworm chromosomes. The results of the experiments were as follows: (1) Pro-metaphase chromosomes showed no distinct primary constriction even after treatment with hypotonic solution, (2) sister chromatids separated in parallel along the entire length of the chromosome at mitotic anaphase, (3) chiasmata underwent complete terminalization during diakinesis and thus chromosome dyads were always connected end-to-end by a terminal chiasma at metaphase I, (4) radiation-induced aberrant chromosomes were stably transmitted throughout a number of cell generations, and (5) although the homomorphic bivalents generally orientated axially at metaphase I and equatorially at metaphase II, this normal sequence tended to be inverted or modified in the X-ray-induced aberrant chromosomes and in the trivalent of the F1 hybrid silkworms. These observations may be best interpreted by assuming the holocentric nature of silkworm chromosomes.

Disomic and ditelosomic additions of diploid agropyron elongatum chromosomes to triticum aestivum

Abstract: A set of disomic addition lines was produced in which each chromosome of Agropyron elongatum (2n = 14) was added to the chromosome complement of Triticum aestivum cv. Chinese Spring. In addition a ...

Abnormal X chromosomes in man: Origin, behavior and effects

Abstract: Abnormal human X chromosomes, their origin, phenotypic effects, and especially their inactivation are reviewed. In cases of balanced reciprocal X-autosomal translocations (Table 2), almost always the normal X is inactivated. Most of such patients suffer from gonadal dysgenesis, which might be caused either by functional hemizygosity for a recessive gene or by a position effect resulting from a rearrangement involving a certain region of Xq. In cases with 46 chromosomes and an unbalanced X-X translocation, the translocation chromosome is inactivated; in most such patients, an X0 cell line is also present (Table 3). Some of the possible modes of origin of such translocations are presented in Fig. 1; these also explain the occurrence of the X0 cell lines. In patients with 46 chromosomes and an unbalanced X-autosomal translocation, the whole translocation chromosome seems to be inactivated, if the autosomal segment is attached to Xp. If on the other hand the segment is, attached to Xq, inactivation seems to be limited to the X part (Fig. 3). There are reasons for assuming the existence of an inactivation center without which an X chromosome cannot be inactivated. This center would be located on the proximal part of Xq. (Abnormal chromosomes with two such centers tend to form bipartite Barr bodies.) If 2 X chromosomes possess an inactivation center each, they would originally be inactivated at random, it then being left to selection to determine the final frequencies of the cell lines with different inactivation patterns. The phenotypic effects of monosomy, disomy and trisomy for different parts of Xp and Xq are discussed (Fig. 3).

Bleomycin-induced Damage in Prematurely Condensed Chromosomes and Its Relationship to Cell Cycle Progression in CHO Cells

Abstract: The phenomenon of premature chromosome condensation, which involves the fusion of mitotic with interphase cells, was applied to the study of bleomycin-induced chromosome damage in Chinese hamster ovary cells. Examination of the prematurely condensed chromosomes immediately after bleomycin treatment revealed a 5 to 9 times higher incidence of chromosome aberrations than the incidence observed in mitotic chromosomes. Attempts to understand the cause for the existence of such a wide difference between prematurely condensed and mitotic chromosomes revealed the following: ( a ) bleomycin treatment (25 µg/ml for 30 min) had no effect on the progression of cells from mitosis to G1 or from G1 to S; ( b ) the rate of progression of S and G2 phase cells into mitosis was slower in the treatment than in the control; ( c ) nearly one-half (44%) of the G2 cells failed to enter mitosis even at 7 hr after the treatment; ( d ) about one-third of the aberrations (gaps and breaks) observed in the prematurely condensed chromosomes were repaired within 60 min after treatment. There was an indication that cells with extensive chromosome damage failed to enter mitosis, and hence they were blocked in G2 until the damage was repaired to tolerable levels. The data also suggested the existence of a maximum limit for the amount of chromosome damage that a cell can carry and still enter mitosis.

Cytogenetic studies on human lymphoblastoid cell lines from Burkitt's lymphomas and other sources.

Abstract: The occurrence and incidence of a characteristic banding abnormality in a No. 14 chromosome has been studied in Burkitt-lymphoma-derived and certain other EB virus-associated lymphoblastoid cell lines. The abnormality was readily detected in 7 out of 7 Burkitt lines, and when present could be seen in 100% of cells with recognizable No. 14 chromosomes. In contrast, the abnormality was not observed in 775 cells from 31 infectious mononucleosis-derived lines nor in 450 cells from 18 lines obtained from cord blood lymphocytes experimentally transformed by EB virus in vitro. The significance of the abnormality as an indication of cells transformed by the virus in vivo is discussed, and the importance of this considered in relation to a possible oncogenic role for EB virus in man.

DNA Replication in the Chromosomes of Eukaryotes

Abstract: The first experimental evidence that the DNA of eukaryotic chromosomes replicates semi-conservatively was provided by Taylor et al., 1957. Root-tip cells of the broad bean, Vicia faba, were allowed to incorporate tritiated thymidine during a period of DNA synthesis (S-phase), were fixed at the following mitosis, and examined by autoradiography. Each labelled chromosome showed radio-activity in both chromatids. Cells similarly labelled, but followed by a time before fixation in the absence of precursor sufficient to complete another S-phase and to reach the next mitosis (i.e. the second mitosis after labelling) showed radioactivity in only one chromatid at any location along each chromosome. These observations, now known to be valid for all eukaryotic chromosomes that have been studied, are evidence not only for semi-conservative replication of DNA as such, but also for the proposition of uninemy, i.e. that each chromatid of a eukaryote contains only one double helix of DNA.

Somatic cell hybrids between mouse peritoneal macrophages and SV40-transformed human cells. I. Positive control of the transformed phenotype by the human chromosome 7 carrying the SV40 genome.

Abstract: Fusion of mouse peritoneal macrophages with SV40-transformed human cells, deficient in hypoxanthine guanine phosphoribosyltransferase, resulted in the formation of transformed somatic cell hybrids which contained, without exception, the human chromosome 7 carrying the SV40 genome. It is postulated that the hybridization of mouse nondividing cells with human cancer cells could permit the identification of the human "oncogenic" chromosome(s) present in human cancer cells, since such chromosome(s) should be retained by the totality of the mouse-human hybrid cells.

The internal order of the interphase nucleus.

Abstract: This paper has two parts. The first one is theoretical, whereas in the second, some experimenteal results are reported. Part 1: Theoretical Considerations. Comings' considerations on an ordered arrangement of chromatin in the interphase nucleus are used as a basis for further investigations and calculations in order to establish a preliminary model of the interphase nucleus. Information on the amount of DNA of a diploid human nucleus, on the degree of spiralization of chromatin threads found in electron microscopy, and measurements of salivary gland chromosomes was used to estimate the lengths of the entire interphase chromosomes. The number of fixing points-pores—was indirectly calculated proposing a model of an internal order of the chromatin threads. This number was found in concord with a direct calculation of the number of pores in the nuclear membrane based on results from electron microscopy. Part 2: Experimental Results and Discussion. In the second part of this study, an approach was made as to how to arrange chromosomes and chromosome segments in their proximity to each other. Results of cytogenetic studies of newborn babies and abortions, of cells from patients with Bloom's syndrome and Fanconi's anemia and normal cells treated with Mitomycin C and Trenimon, are thought to be informative under certain suppositions for the problem, which chromosome or chromosome parts are situated in proximity to each other. The symmetrical and equal interchanges seen, for example, in Bloom's syndrome are an indication of somatic pairing during the time of reunion. Therefore, the unequal interchanges in the same syndrome in which different chromosomes are involved should give evidence for proximity of nonhomologous chromosomes. Arguments for and against a temporal and spacial hypothesis for somatic pairing are discussed. The differing frequencies of chromosomes involved in Robertsonian translocations in man are informative for proximities of satellite regions at the nucleolus. Nucleolus and sex chromatin could be used as fixed points in a model of the interphase nucleus in which finally the absolute localization of the chromosomes will be discovered. The discussion points out promising methods for further investigations on the subject and mentions problems which could be attacked if the approach described here leads to a model of internal order in the interphase nucleus.

Bloom's syndrome and Fanconi's anemia: demonstration of two distinctive patterns of chromosome disruption and rearrangement.

Abstract: A comparison of the patterns of chromosome breakage and rearrangements was made using lymphocytes from one patient with Bloom's syndrome and one with Fanconi's anemia Chromatid and isochromatid gaps and breaks were increased in frequency in both conditions In Fanconi's anemia, more aberrations per aberrant cell occurred than in Bloom's syndrome The relative numbers of the various classes of interchanges and the chromosome regions affected differed strikingly In Bloom's syndrome, homologous chromosomes had formed most of the interchanges, while in Fanconi's anemia non-homologous chromosomes were preferentially involved in the interchanges The patterns formed by brakage, including breaks involved in interchanges, show a non-random distribution of the lesions in both conditions

New selective Giemsa technique for human chromosomes, Cd staining.

Abstract: AFTER the introduction of the quinacrine fluorescence method1, several Giemsa staining techniques have been developed for karyotype analysis of human chromosomes. Pardue and Gall2, originally noticed a denser staining of centromeric regions of chromosomes after in situ hybridisation of mouse chromosome preparations with mouse satellite DNA followed by Giemsa staining. This initial approach was modified by Arrighi and Hsu3 who omitted DNA hybridisation. Later, Sumner et al.4 left out treatment with RNase and HC1 as well. Finally, McKenzie and Lubs5 treated chromosomes with HCl and 2×SSC only. These modified Giemsa procedures all produce densely stained regions of one or both chromosome arms close to the centromere. These C-band procedures also stain the secondary constriction of chromosome 1, 9 and 16, as well as the distal part of the Y chromosome. Satellites that stain brightly by Q-band techniques are also revealed by these methods.

Assignment of the gene for galactokinase to human chromosome 17 and its regional localisation to band q21-22

Abstract: PROGRESS in somatic cell genetics now allows more rapid and precise localisation of genes within the human genome. A large number of mouse × human hybrid cell lines are available, permitting the investigator to choose, for phenotype assay, lines with a particular reduced human chromosome complement. An increasingly large number of hybrid lines carrying rearranged chromosomes are also becoming available for regional localisation studies. We have used such hybrid cell lines to assign a gene coding for galactokinase (EC 2.7.1.6) to human chromosome 17 and to further localise the gene to band 21–22 on the long arm of the chromosome. Results from this study have provided new information Regarding the functioning of the genes coding for the Leloir pathway enzymes in man1, and have revealed a relatively close and potentially useful linkage between the genes for galactokinase and for thymidine kinase (EC 2.7.1.21).

The relationship between chromosomal aberrations, survival and dna repair in tumour cell lines of differential sensitivity to x-rays and sulphur mustard.

Abstract: A pair of cultured rat lymphosarcoma cell lines (Yoshida) with a pronounced differential sensitivity to killing with sulphur mustard (SM), but with the same sensitivity to X-rays, was examined for chromosome damage and DNA repair replication after treatment with these agents. A pair of mouse lymphoma cell lines (L5178Y) with a differential sensitivity to X-rays was similarly investigated. SM-resistant Yoshida cells suffered much less chromosome damage than sensitive cells in spite of equal alkylation of DNA, RNA and protein in sensitive and resistant cells. The pair of Yoshida cell lines sustained the same amount of chromosome damage after X-irradiation. Much less chromosome damage was observed in the radiation-resistant lymphoma cell line than in the sensitive line after X-irradiation. No differences was found between the pairs of cell lines in their capacities for repair replication after SM or X-ray treatment. Thus, the drug and radiation resistance is accompanied by, and perhaps mediated through, a reduced amount of induced chromosome damage but is not quantitatively related to the capacity for DNA repair replication. Apart from small differences in modal chromosome numbers there are no obvious karyotype differences between the sulphur mustard-sensitive and -resistant Yoshida cells or between the radiation-sensitive and -resistant lymphoma cells.

The manifestation of chromosome rearrangements in unordered asci of Neurospora.

Abstract: Rapid, effective techniques have been developed for detecting and characterizing chromosome aberrations in Neurospora by visual inspection of ascospores and asci. Rearrangements that are detectable by the presence of deficient, nonblack ascospores in test crosses make up 5 to 10% of survivors after UV doses giving 10-55% survival. Over 135 rearrangements have been diagnosed by classifying unordered asci according to numbers of defective spores. (These include 15 originally identified or analyzed by other workers.) About 100 reciprocal translocations (RT's) have been confirmed and mapped genetically, involving all combinations of the seven chromosomes. Thirty-three other rearrangements generate viable nontandem duplications in meiosis. These consist of insertional translocations (IT's) (15 confirmed), and of rearrangements that involve a chromosome tip (10 translocations and 3 pericentric inversions). No inversion has been found that does not include the centromere. A reciprocal translocation was found within one population in nature. When pairs of RT's that involve the same two chromosome arms were intercrossed, viable duplications were produced if the breakpoints overlapped in such a way that pairing resembled that of insertional translocations (27 combinations).—The rapid analytical technique depends on the following. Deficiency ascospores are usually nonblack (W: "white") and inviable, while nondeficient ascospores, even those that include duplications, are black (B) and viable. Thus RT's typically produce 50% black spores, and IT's 75% black. Asci are shot spontaneously from ripe perithecia, and can be collected in large numbers as groups of eight ascospores representing unordered tetrads, which fall into five classes: 8B:0W; 6B:2W, 4B:4W, 2B:6B, 0B:8W. In isosequential crosses, 90-95% of tetrads are 8:0. When a rearrangement is heterozygous, the frequencies of tetrad classes are diagnostic of the type of rearrangement, and provide information also on the positions of break points. With RT's, 8:0 (alternate centromere segregation) = 0:8 (adjacent-1), 4:4's require interstitial crossing over in a centromere-break point interval, and no 6:2's or 2:6's are expected. With IT's, duplications are viable, 8:0 = 4:4, 6:2's are from interstitial crossing over, 0:8's or 2:6's are rare. Tetrads from RT's that involve a chromosome tip resemble those from IT's, as do tetrads from intercrosses between partially overlapping RT's that involve identical chromosome arms.—Because viable duplications and other aneuploid derivatives regularly occur among the offspring of rearrangements such as insertional translocations, care must be taken in selecting stocks, and original strains should be kept for reference.

The rep Mutation III. Altered Structure of the Replicating Escherichia coli Chromosome

Abstract: The rep gene function of Escherichia coli is essential for the replication of P2 and φX174 double-stranded deoxyribonucleic acid (DNA). Compared with isogenic rep+ strains, rep mutants show the following characteristics: larger cell size, more DNA per cell, and a slightly lower DNA/mass ratio. The replicating rep chromosomes show a steeper gradient of marker frequencies and contain more replicating forks per chromosome. The nucleoid body of rep mutants sediments faster and contains more DNA. We deduce that the rep function is required for the “normal” replication of the E. coli chromosome and that in its absence the E. coli chromosome replicates in an altered manner, perhaps involving slower-moving replicating forks.

The chromosomal localisation of human satellite DNA I

Abstract: The major concentrations of human satellite DNA I (1688 g/ml) have been localised on human chromosome preparations by the technique of in situ hybridisation using radioactive complementary RNA synthesised in vitro Chromosomes were identified by prior study using quinacrine fluorescence microscopy The satellite DNA is concentrated, mainly in centromeric constitutive heterochromatin, on many chromosomes but is especially obvious in the fluorescent distal segment of the Y chromosome

Analysis of the chromosome aberrations induced by x-rays in somatic cells of drosophila melanogaster

Abstract: A technique has been perfected for enabling good microscope preparations to be obtained from the larval ganglia of Drosophila melanogaster . This system was then tested with X-rays and an extensive series of data was obtained on the chromosome aberrations induced in the various stages of the cell cycle.—The analysis of the results obtained offers the following points of interest: (1) There exists a difference in radio-sensitivity between the two sexes. The females constantly display a greater frequency of both chromosome and chromatid aberrations. They also display a greater frequency of spontaneous aberrations. (2) In both sexes the overall chromosome damage is greater in cells irradiated in stages G2 and G1. These two peaks of greater radiosensitivity are produced by a high frequency of terminal deletions and chromatid exchanges and by a high frequency of dicentrics, respectively. (3) The aberrations are not distributed at random among the various chromosomes. On the average, the Y chromosome is found to be more resistant and the breaks are preferentially localized in the pericentromeric heterochromatin of the X chromosome and of the autosomes. (4) Somatic pairing influences the frequency and type of the chromosome aberrations induced. In this system, such an arrangement of the chromosomes results in a high frequency of exchanges and dicentrics between homologous chromosomes and a low frequency of scorable translocations. Moreover, somatic pairing, probably by preventing the formation of looped regions in the interphase chromosomes, results in the almost total absence of intrachanges at both chromosome and chromatid level.

The genes for ribosomal RNA in diploid and polytene chromosomes of Drosophila melanogaster

Abstract: The proportion of the Drosophila genome coding for ribosomal RNA was examined in DNA from both diploid and polytene tissues of Drosophila melanogaster by rRNA-DNA hybridization. Measurements were made on larvae with one, two, three and four nucleolus organizer regions per genome. In DNA from diploid tissues the percent rDNA (coding for 28S and 18S ribosomal DNA) was found to be in proportion to the number of nucleolus organizers present. The number of rRNA genes within a nucleolus organizer therefore does not vary in response to changes in the number of nucleolus organizers. On the other hand, in DNA from cells with polytene chromosomes the percent rDNA remained at a level of about 0.1% (two to six times lower than the diploid values), regardless of either the number of nucleolus organizers per genome or whether the nucleolus organizers were carried by the X or Y chromosomes. This independence of polytene rDNA content from the number of nucleolus organizers is presumably due to the autonomous polytenization of this region of the chromosome. When the rDNA content of DNA from whole flies is examined, both the rDNA additivity of the diploid cells and the rDNA independence of polytene cells will affect the results. This is a possible explanation for the relative rDNA increase known to occur in X0 flies, but probably not for the phenomenon of rDNA magnification. — In further studies on DNA from larval diploid tissues, the following findings were made: 1) the Ybb-chromosome carries no rDNA; 2) flies carrying four nucleolus organizers do not tend to lose rDNA, even after eleven generations, and 3) the nucleolus organizer on the wild type Y chromosome may have significantly less rDNA than does that on the corresponding X chromosome.

Mapping human autosomes: evidence supporting assignment of rhesus to the short arm of chromosome No. 1.

Abstract: Rh-negative erythrocytes were found in the blood of an Rh-positive man suffering from myelofibrosis. Nucleated hemopoietic precursors were also circulating in his blood, and these cells had an abnormal chromosome complement from which identifiable chromosome segments had been deleted. Correlation of the serological and cytogenetic findings, combined with previous data, indicates that the Rhesus blood group locus is on the distal portion of the short arm of chromosome No. 1.

Location of human satellite DNAs on the Y chromosome

Abstract: THE technique of in situ hybridisation of radioactively labelled DNA or RNA to the denatured DNA in metaphase chromosomes provides a powerful and popular method for identifying the chromosomal location of specific repeated DNA sequences1,2. In man, this technique has been used to map the ribosomal cistrons (ref. 3 and H.J.E., M. L. Pardue, and R.A.B., in preparation) and to examine the chromosomal location of three of the four known satellite DNAs4–8. Satellite II (ref. 6) was found in the centromeric hetero-chromatic regions (C band) of chromosome 1 and in the C bands of one C group (chromosome 9) and one E group chromosome pair (tentatively identified as chromosome 16). Satellite III (ref. 8) was found mainly in the C band of chromosome 9, with some in the centromere/short arm regions of the D and G group chromosomes, and possibly in the C bands of chromosomes 1 and 16. The satellite DNA investigated by Saunders et al.7 (which is probably identical to satellite IV of Corneo et al.5) was only positively identified in the C band of chromosome 9, although other regions of hybridisation were noted. In all these studies on satellite DNAs, the auto-radiographic observations were limited because no general chromosome identification was possible. Thus, only major sites of hybridisation could be detected and in some instances the locations of these sites were in doubt.

Segmental aneuploidy and enzyme activity as a method for cytogenetic localization in drosophila melanogaster.

Abstract: A method of mapping genes which specify enzymes without the necessity of obtaining genetic variants has been explored. Three enzymes whose structural genes have known genetic positions were chosen to see if the relationship between gene dosage and enzyme activity could be used as a tool in cytological localization. Zw, the gene specifying G6PD, is located in the X chromosome region, 18D-18F. The structural gene for 6PGD, Pgd, maps in the X chromosome bands 2C1-2E1. Idh-NADP, the gene which specifies IDH-NADP, is found on the third chromosome, in bands 66B-67C.

The gorilla karyotype: chromosome lengths and polymorphisms

Abstract: Metaphase chromosome preparations of three male and one female Gorilla gorilla were stained to demonstrate quinacrine, Giemsa, centromeric heterochromatin, and, in one case, reverse

Regulation of enzyme activities in Drosophila. I. The detection of regulatory loci by gene dosage responses.

Abstract: In order to detect regulatory genetic sites in the autosomes of Drosophila melanogaster, the levels of X-linked glucose-6-phosphate dehydro-genase and autosomally linked α-glycerophosphate and isocitrate dehydrogenases have been monitored in extracts of flies aneuploid for regions of chromosomes II and III. In addition to expected structural gene dosage responses of α-GPDH and IDH, flies hyperploid for several autosome regions were found to display altered levels of one or more of the enzymes studied. While IDH activity was increased in flies hyperploid for segments of both chromosomes II and III, α-GPDH activity was decreased in specific hyperploids for chromosome II regions only. The latter group of segmental aneuploids were normal with respect to levels of chromosome II-linked alcohol dehydrogenase. To test if the observed responses were due to dosage changes of discrete genes lying within the larger effective segments, flies aneuploid for subdivisions of the chromosome segments 21A-25CD, 35A–40, and 70CD–71B were assayed. For two of these large segments so analysed, the apparent effects were attributable to specific small subdivisions, suggesting the presence of discrete regulatory sites within the latter. For the 35A–40 region the α-GPDH effect observed for subdivisions was not sufficient to account for the large α-GPDH decrease seen in flies hyperploid for the large, inclusive region. These observations are discussed with respect to the possible bases of effect of regulatory elements on enzyme activity.