Showing papers on "Chromosome published in 1968"

Late DNA synthesis in heterochromatin.

Abstract: It seems to be a rule of chromosome replication that heterochromatin synthesizes its DNA at a later stage than the rest of the chromosome.

Chromosome studies in the superfamily Bovoidea.

Abstract: The chromosome morphology of about 50 species of Bovoidea has now been investigated. Although the diploid number varies from 30 to 60 among these species, the fundamental number (NF) varies only (with but three exceptions) from 58 to 62. This indicates an almost exclusive use of the Robertsonian fusion mechanism of karyotype evolution in this group of species which represent 30 different genera. All known cytogenetic information on the Bovoidea has been summarized and a complete bibliography is presented for each species. Karyotypes and data on a number of previously unstudied species are presented.

The incorporation of alien disease resistance in wheat by genetic interference with the regulation of meiotic chromosome synapsis

Abstract: 1. Triticum aestivum ssp. vulgare variety Chinese Spring (2n = 6x = 42) is susceptible to yellow rust caused by Puccinia striiformis while the wild annual grass Aegilops comosa (2n = 14) is resistant to all the physiologic races for which it has been tested.2. By a backcrossing programme initiated from Chinese Spring × Ae. comosa hybrids, using Chinese Spring as the recurrent parent, a line was isolated with a single chromosome of Ae. comosa, determining rust resistance, added to the full complement of Chinese Spring.3. The alien chromosome substituted with good genetic compensation only for the chromosomes of homoeologous group 2 of Chinese Spring. This demonstrated that the chromosome determining rust resistance is in homoeologous group 2. It was designated 2M since Ae. comosa has the M genome.4. In order to induce recombination between 2M and its wheat homoeologues, hybrids were made using Ae. speltoides which has the capacity to suppress the activity of chromosome 5B that normally prevents homoeologous synapsis. A backcrossing programme, using Chinese Spring as the recurrent parent, was reinitiated from the 29-chromosome hybrids carrying chromosome 2M and the haploid complements of Chinese Spring and Ae. speltoides.5. Selection was practised for rust resistance and ultimately a resistant plant with 42 chromosomes, that formed 21 bivalents at meiosis, was isolated. This plant was heterozygous for a dominant rust resistance allele (Yr8) derived from Ae. comosa. Homozygotes were isolated in its progeny and in this way the rust resistant breeder's variety, Compair, was established.6. Compair differs from Chinese Spring in its yellow rust resistance which was shown to be determined by a chromosome corresponding to 2D of Chinese Spring. This chromosome of Compair has the short arm, the centromere and a proximal segment of the long arm of chromosome 2M and a distal segment of the right arm of chromosome 2D. The modified chromosome, which is designated 2M/D, arose by homoeologous recombination in the Ae. speltoides hybrid or in the immediately succeeding backcross generations. Chromosome 2M/D carries the Yr8 gene in the proximal segment of the long arm derived from chromosome 2M.7. In hybrids between Compair and standard wheat varieties, chromosome 2M/D pairs regularly with chromosome 2D so that regular segregation of Yr8 can be expected and Compair treated like any other parental variety in wheat hybridization programmes.8. This work illustrates the way that homoeologous recombination can be induced and exploited both in cytogenetic analysis in wheat and in practical breeding work. The nature of the meiotic synapsis of chromosome 2M/D with its partial homologues raises questions concerning the means by which chromosome 5B influences the specificity of meiotic synapsis.

Cytogenetic analysis of the tomato genome by means of induced deficiencies

Abstract: Cytological studies of 74 deficiencies of tomato chromosomes induced by radiation and identified by the pseudo-dominant technique reveal the loci of 35 genes on 18 of the 24 arms of the complement. These findings integrated with data obtained from various trisomic types establish centromere positions, orientation of linkage groups, and markers on all but three of the arms. The prospects of obtaining a specific kind of deficiency for a given region were found to depend on : (1) kind of radiation applied, (2) (non-random) breakage frequency in different parts of the chromosome, (3) stability of broken ends, (4) tolerance of deficiency in different parts of the genome, and (5) relative vigor of the mutant homozygote used to detect the deficiency. Aspects of the frequently observed non-homologous pairing phenomenon are presented and discussed. Marker genes whose loci are known appear to be non-randomly distributed between and within chromosomes. Chromosome exchanges as determined by genetic crossing over and cytologically observed chiasmata are likewise non-randomly distributed between and within chromosomes.

The replicative organization of DNA in polytene chromosomes of Drosophila hydei.

Abstract: Salivary-gland nuclei ofDrosophila hydei were pulse-labeledin vitro with3H-thymidine and studied autoradiographically in squash preparations. The distribution of radioactive label over the length of the polytene chromosomes was discontinuous in most of the labeled nuclei; in some nuclei the pattern of incorporation was continuous. Comparison of the various labeling patterns of homologous chromosome regions in different nuclei showed that specific replicating units are replicated in a specific order. By combining autoradiography with cytophotometry of Feulgen-stained chromosomes, it was possible to correlate thymidine labeling of specific bands with their DNA content. The resulting data indicate that during the S-period many or perhaps all of the replicating units in a salivary-gland nucleus start DNA synthesis simultaneously but complete it at different times. Furthermore, the data support the hypothesis that the chromomere is a unit of replication or replicon. The DNA content of haploid chromomeres was found to be about 5×10-4 pg for the largest bands inDrosophila hydei. From the results of H3-thymidine autoradiography and Feulgen-cytophotometry on neuroblast and anlage nuclei it was concluded that during growth of the polytenic nucleus heterochromatin is for the most part excluded from duplication. The results of DNA measurements in interbands of polytene chromosomes do not agree with a multistrand structure for the haploid chromatid. A chromosome model is proposed which is in accordance with the reported results and with current views concerning the replicative organization of chromosomes.

Human-Mouse Somatic Cell Hybrids with Single Human Chromosome (Group E): Link with Thymidine Kinase Activity

Abstract: Mouse somatic cells lacking thymidine kinase were mixed in culture with human diploid cells lacking hypoxanthine guanine phosphoribosyl transferase, and hybrid cells were isolated and maintained in a selective medium containing hypoxanthine, aminopterin, and thymidine. The hybrid cells at the time of isolation had karyotypes consisting predominantly of mouse chromosomes but with one human chromosome, a submetacentric member of group E, apparently giving thymidine kinase to the hybrid cell. However, after long-term propagation in the selective medium this chromosome has been lost, although cells continue to show thymidine kinase activity as demonstrated by the incorporation of 3H-thy-midine into DNA in the hybrid cell. The hybrid cells have only mouse electro-phoretic variants for glucose-6-phosphate dehydrogenase, lactate dehydrogenase, and malate dehydrogenase, suggesting that the human genetic loci for these enzymes are not represented in the hybrid genome and may be unlinked to that for thymidine kinase.

Properties and Uses of Human–Mouse Hybrid Cell Lines

Abstract: Staged reduction of the chromosome complement of human–mouse hybrid cells has made possible the identification of the chromosome bearing the human gene for thymidine kinase. Effects of human chromosomes on the growth rate of hybrid cells are examined and the possibility of making further chromosomal assignments for human autosomal genes is discussed.

On the diploid state of the fish order Ostariophysi

Abstract: Our previous study on the order Ostariophysi was limited to members of the family Cyprinidae, suborder Cyprinidea. It was shown that the carp and the goldfish with 104 chromosomes and a DNA value of 50% that of mammals are tetraploid, as the diploid species of this family has 50–52 chromosomes and a 25% DNA value. In order to obtain some idea as to how many changes in DNA values and chromosome complements have occurred among diploid members of Ostariophysi, the study was expanded to cover members of the families Cobitidae and Characinidae of the suborder Cyprinidea as well as members of the families Ictarulidae and Loricaridae of the suborder Siluroidea. Diploid chromosome numbers varied from 50 to 98 and DNA values from 27–51% that of mammals. Apparently, diploid members of Ostariophysi underwent extensive chromosomal rearrangements as well as steady increases in DNA contents by regional duplication of chromosomal segments.

Extra Replications in the ?DNA-puffs? ofSciara coprophila

Abstract: Using the Zeiss UMSP-1, a spectrophotometric study was made of DNA increase in three “DNA-puffs” located on chromosome II ofSciara coprophila. Each puff showed excessive and disproportionate synthesis. During the course of study it became apparent that the DNA in at least one of the puffs (the most proximal) arises from a number of cytological subunits (bands). When the DNA in the entire puff was measured, only irregular synthesis was revealed. On the other hand, when DNA increase in one of the bands was measured, the absorbancy values formed a geometric series, indicating that the extra DNA arises by additional complete rounds of replication.

Translocations involving triticum chromosomes and agropyron chromosomes carrying rust resistance

Abstract: Two programs have been carried out in which irradiation was used to translocate a gene for rust resistance from a Agropyron to a wheat chromosome. In one case, 1 out of 7 translocations and in another 1 out of 4 were transmitted normally through the gametes and proved to involve a wheat chromosome homoeologous to the Agropyron chromosome. It is suggested that the translocations are not randomly distributed among the wheat chromosomes and that this is because homoeologous chromosomes are not randomly distributed in the somatic nucleus.

Direct evidence for presence of Ph-1 chromosome in erythroid cells.

Abstract: In a patient with primary hyperaldosteronism the rates of net transport and of unidirectional fluxes of sodium, potassium, and water in the intact colon were measured before and after removal of the adrenocortical turnour, by perfusing the colon with an isotopically labelled test solution introduced into the caecum through a tube passed by mouth. The results in this patient were compared with those in eight control subjects. Before removal of the aldosterone-producing turnour the colon of the patient secreted potassium at four to five times the rate in control subjects. The unidirectional flux of potassium into the colonic lumen was greatly enhanced and the daily loss of potassium in the faeces increased. The rates of potassium transport returned to within the range observed in control subjects after the removal of the tumour.

The multiple sex chromosome system of American leaf-nosed bats (Chiropter, Phyllostomidae).

Abstract: Karyological examination of 26 species of bats from the family Phyllostomidae revealed two Y chromosomes (XY1Y2) in six species involving three genera All females are of the XX

Genome relationships in tetraploid avena

Abstract: Relationships between the A and B genomes of the tetraploid Avena species (A. magna excluded) and between these and the AS genome of the diploid A. hirtula and strigosa were studied in triploid (ASAB) and tetraploid (ASASAB) hybrids. Chromosome affinities were estimated on the basis of the karyotypes and the pairing behaviour of the chromosomes.The main findings were:1. The AS karyotype of the 2x and the A of the 4x species were identical and the chromosomes of the genomes A and B were similar. No difference was noticeable in the karyotypes of the 4x species studied. A nucleolar chromosome appeared from the B set in the 3x hybrids. It was concluded that the B genome is probably a modified form of A.2. All the chromosomes were capable of pairing in the ASAB and ASASAB hybrids. High degree of homology between the AS and A genomes was indicated by the high frequency of ring bivalents and ring-rod trivalents. The synaptic success of the B genome chromosomes (up to six trivalents) was interpreted as homoeology...

Effect of aflatoxin on human leukocytes.

Abstract: SummaryAflatoxin inhibits mitosis and causes breakage and translocations in the chromosomes of cultured human leukocytes. The nonrandom pattern of breakage was confined mainly to the largest chromosomes of the human complement. Chromosome no's. 1 and 2 were particularly affected, while groups E, F, and G exhibited a lower than expected frequency of breaks.The effect of aflatoxin on human leukocytes is of the delayed type which is characteristic of chromosome breaking compounds such as alkylating agents 11,12.

Chromosome polymorphism in the species of the GENUS Cercopithecus.

Abstract: The chromosomes of 27 animals belonging to 11 species of the genus Cercopithecus were studied.The number of chromosomes for the different species studied, varies from a minimum of 2n=54 to a max. of 2n=72. In individuals belonging to the same species, a different number of chromosomes has been noted.The morphological analysis did not reveal any clear relation between the total number of chromosomes and the number of acrocentric chromosomes.The total length of the caryotype measured on 20 metaphase plates, increases with the increase of the number of the chromosomes.On the basis of these two data I suggest the hypothesis that the variation in the number of the chromosomes of the genus Cercopithecus is originated by the reduplication of single chromosomes.

Nonrandomness of translocations in man: preferential entry of chromosomes into 13-15-21 translocations.

Abstract: Lymphocytes from 20 individuals with Down's syndrome due to 13-15/21 centric-fusion translocations were studied by autoradiography after continuous late labeling with tritiated thymidine. In no case was chromosome 13 involved; chromosome 14 was involved in 18 cases, and chromosome 15 in two cases. These results are similar to those from 13 previously studied cases and indicate that the entry of chromosomes 13-15 into translocations is nonrandom. This nonrandomness is not a simple function of chromosome size or shape, since chromosomes 13-15 are acrocentrics of similar size.

The influence of B-chromosomes upon the nuclear phenotype in rye

Abstract: Quantitative studies on the ffects of B-chromosomes in rye upon variation of the nuclear phenotype showed that B's: (i) influence the phenotype of the A-chromosomes at metaphase of mitosis, (ii) increase the amount of nuclear DNA in proportion to their number present, (iii) have a structural organisation different to that of the A-chromosomes, (iv) influence the structure of the interphase nucleus in respect of non-permanent chromosome material.

Asynchrony of DNA replication and mitotic spiralization along heterochromatic portions of Chinese hamster chromosomes.

Abstract: Sequence of DNA synthesis and mitotic chromosome spiralization along heterochromatic portions of the sex (X1X2) and of some marker chromosomes in cultured Chinese hamster cells were studied, employing two methods: study of segmentation pattern caused in chromosomes with colcemid, and autoradiography with tritiated thymidine. The heterochromatic portions of all chromosomes studied were characterized by striking internal asynchrony of DNA replication. In particular, they had segments that replicated relatively early. The short arm of the X2 chromosome, heterochromatic in female somatic cells, had at least three such segments. Replication patterns of the long arms of the X1 and X2 chromosomes were different. In X1 this arm contains several segments showing relatively early replication. The long arm of X2 had no similar segments. The possible significance of the data obtained is discussed with regard to the problem of genetic inertness of heterochromatin. At the terminal stage of the S period, H3-thymidine seems to be incorporated into condensed chromatin of interphase nuclei. On the basis of the data obtained, it is proposed that during replication of heterochromatin consecutive despiralization of parts of it takes place.

The relationship of mutation rate per roentgen to DNA content per chromosome and to interphase chromosome volume.

Abstract: LOCALIZED phenot.ypic changes in petal color following X-irradiation and acute or chronic gainma irradiation have been reported for several species of higher plants (IBA, MA'rSUBARA, INOKOSHI, OKA and MESHITSUKA 1964; MATSUBARA, IBA, OKA and MESHITSUKA 1964, MoEs 1966; GUPTA and SAMATA 1963, 1964; RICHTER and SINGLETON 1955; SAGAWA and MEHLQUIST 1957; NEZU 1963b; MESHITSUKA, OKA, MATSUBARA and IBA 1963; MESHITSUKA, OKA, IBA, MATSUBARA and INOKOSHI 1963). Mutation rates for individual loci controlling flower color have been published for Antirrhinum majus (CUANY, SPARROW and POND 1958), Zmpatiem; balsamina (ALSTON and SPARROW 1962), Petunia hybrid~, Tradescantia (clone 02), Lilium testaceum (SPARROW, CUANY, MIKSCHE and SCHAIRER 1961), and Tulipa (NEZU 1963a). The possibility that mutation rate per roentgen (CUANY, SPARROW and JAHN 1958; CUANY, SPARROW and FOND 1958; SPARROW, CUANY, MIKSCHE and SCHAIRER 1961) or frequency of chromosome deletion per nucleus per roentgen (SPARROW and EVANS 1961) might be related to certain nuclear parameters was recognized several years ago, and some of the present data were reported in preliminary form in 1962 (SHAVER and SPARROW 1962). Further experiments confirming the relationship between chromosome size and induced somatic mutation rate are reported here (see also BAETCKE, SPARROW, SHAVER and POND 1967). It has been shown previously that plant radiosensitivity as measured by lethality. growth inhibition. etc. also depends partially on DNA content per chromosome (SPARROW and .MIKSCHE 1961; SPARROW, SPARROW, THOMPSON and SCHAIRER 1965; BAETCKE, SPARROW, NAUMAN and SCHWEMMER 1967). It therefore seemed appropriate to test whether mutation rate also might be at least partly dependent on DNA content per cell or per chromosome. The data presented below show that such a relationship does exist.

Cytological Studies in Dioscoreaceae

Abstract: Cytological studies of ten species and a few varieties of Dioscorea and the monotypic genus Trichopus occurring in South India have been made. The chromosome numbers of South Indian Dioscorea species are seen to occur in multiples of the basic number 10 (40, 60, 80, 90, 100), as in the case of other Asiatic species reported previously. Trichopus zeylanicus (n=14, 2n=28) shows a basic number of 14 not found in any other genus of the Dioscoreaceae so far studied. Cytological data support morphological and anatomical evidence suggesting creation of a separate family for the genus Trichopus.

Evolutionary origin of poa annua l. in the light of karyotypic studies

Abstract: From a karyotype analysis of Poa annua (2n = 28) two large chromosomes, I and II, and one small chromosome, XIV, as well as three chromosome groups containing two, four and five chromosomes have be...

A study on the clonal nature of spleen colonies using chromosome markers.

Abstract: SUMMARY Cytological evidence for the clonal origin of spleen colonies is presented. Karyotypic analysis of the spleen nodules produced by transplants of hematopoietic tissue from radiation chimeras bearing three kinds of chromosome-marked cells showed 41 out of 48 spleen nodules to be composed entirely of one or another of the karyotypes. In the remaining 7 nodules 92 to 98% of the dividing cells in each nodule were of the same type. Since no mixtures were observed in proportions consistent with other than single cell origin, the data lend further support to the clonal hypothesis of origin of the spleen colony.

Factors influencing mammalian X chromosome condensation and sex chromatin formation

Abstract: The aim of this study is to determine why, in contrast to expectations based on the Lyon hypothesis, a variable number of nuclei of cells from mammalian females are sex chromatin negative The frequency of sex chromatin positive nuclei was determined in cell cultures of varying cell densities The cells were derived from seven chromosomally normal human female embryos, one newborn female with an extra E group chromosome and two normal male embryos In all cultures of females the frequency of sex chromatin positive nuclei increased linearly from about 35% to 60% at cell densities of less than one cell per 001 mm2 of culture surface to 90% to 100% at densities of 20 to 125 cells per 001 mm2 This frequency-to-density relationship was independent of the mitotic rate and the rate at which cell density increased When large variations in cell density were produced intentionally on the same glass coverslip, sex chromatin frequency was related to the density of cells in any one area of a coverslip and seemed to be largely independent of the cell density in other parts of the coverslip The frequency of sex-chromatin-like bodies of male cultures remained very low at all cell densities These and other preliminary observations described suggest that, in the nucleus of the female, sex chromatin formation resulting from the condensation of an X chromosome at interphase is not directly related to the mitotic cycle but may be related to the metabolic state of the cell

Chromosome patterns of human leukocyte established cell lines.

Abstract: Of 14 lines of human leukocytes, designated LK1D, LK57, LK60, LK63, LK87A, LK91, SK-L1, SK-L3, SK-L4, SK-L5, SK-L6, SK-L7, RPMI 7216, and RPMI 7466, all were classically diploid or very near-diploid when first examined. All but one showed occasional No. 10 chromosomes with the near terminal secondary constriction seen in Burkitt lymphoma cells in vitro . Nine lines showed accentuation of secondary constrictions at the usual sites on Chromosomes No. 1 and/or No. 16. Exchanges often occurred at these sites. Some cells in various lines showed multiple secondary constrictions or fragmentation (pulverization), but these and other chromosome abnormalities were in lower incidence than in Burkitt lymphoma strains. Many of the abnormalities in these lines may reflect underlying abnormalities of nucleoli or of nucleolar-associated heterochromatin.

The pachytene chromosomes of a diploid medicago sativa

Abstract: Pachytene chromosomes of a diploid Medicago sativa L. were used to construct an idiogram showing chromosome lengths, arm ratios and chromomere distribution. The eight chromosomes were readily disti...