SEARCH · PubMed Health

Results for “diploidization”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources

PubMed1960

Diploid heterozygous hybrids from matings between Escherichia coli and Salmonella typhosa.

An Hfr strain of E. coli K-12 has been shown to mate at low frequency with a number of strains of S. typhosa. The hybrids, selected as lactose positives, retained all other antigenic and biochemical manifestations of the S. typhosa parent. A Lac(+) hybrid, S. typhosa strain 643L(+) was remated with the E. coli Hfr and plated on minimal media containing L-arabinose, D-xylose, L-rhamnose, or L-fucose as the sole carbon sources. Hybrids of the remated strain appeared at high frequency on the plates containing L-arabinose, and could be detected at lower frequencies on plates containing D-xylose, L-rhamnose, and L-fucose. Those selected for D-xylose or L-rhamnose utilization possessed the attributes of segregating diploid heterozygotes being highly unstable and continually segregating a cultural form typical of the S. typhosa parent. The unstable type exhibited most of the biochemical characteristics of the E. coli parent including the ability to produce indol, and also reacted with antiserum to both the E. coli and S. typhosa parent strains, owing to the acquisition of a thermolabile antigen from the E. coli parent. The parent and hybrid strains were examined in detail for changes in patterns of phage susceptibility and virulence. Acquisition of susceptibility to a number of the T phages, a characteristic of the E. coli parent, was observed in one of the hybrid types. A decrease in virulence of the diploid hybrid form of S. typhosa in the mouse virulence test was found.

Animals↗

PubMed1993

Ki-67 and proliferating cell nuclear antigen tumor proliferative indices in DNA diploid colorectal adenocarcinomas. Correlation with histopathologic characteristics and cell cycle analysis with two-color DNA flow cytometry.

The prognostic significance of tumor proliferative activity (TPA) in colorectal adenocarcinomas (CA) determined by proliferating cell nuclear antigen (PCNA) and Ki-67 staining is not well defined. Previous investigations of TPA using Ki-67 immunohistologic studies and flow cytometric (FCM) analysis have found no correlation with conventional histopathologic parameters. To better define the relationship of these various TPA measurements in CA, the authors selected 46 tumors with diploid DNA content previously analyzed by two-color DNA FCM analysis of fresh specimens to more effectively assess actual S-phase fractions (SPFs) from cytokeratin-gated DNA histograms for comparison with the following: (1) immunohistologic Ki-67 and PCNA tumor proliferation indices (TPIs); and (2) conventional histopathologic observations of prognostic import. These data show no significant correlation coefficient between Ki-67 or PCNA TPIs and SPFs derived from FCM analysis; however, the DNA diploid tumor subset categorized as having a greater than median SPF value had a significantly higher mean Ki-67 but not PCNA proliferation index. There was no correlation of any measure of proliferation with any of the eight histopathologic features of known prognostic significance.

Adenocarcinoma↗

PubMed1998

Effect of 3-aminotriazole on anchorage independence and mutagenicity in cadmium- and lead-treated diploid human fibroblasts.

Cadmium and lead have been shown to induce cellular transformations and gene mutations in cultured rodent cells, as well as tumours in live animals. However, the mechanisms by which these metals cause cellular transformations and mutations in human cells have not been explored. In this study, we investigated the abilities of cadmium and lead to induce anchorage-independent transformations and hprt gene mutations in diploid human fibroblasts. Human fibroblasts were exposed to either cadmium acetate (0-60 microM) or lead acetate (0-2 mM) for 24 h. After removal of the metals, the cells were kept in exponential growth for 7 and 9 days before mutation and anchorage-independence assays were taken, respectively. Both cadmium and lead significantly induced anchorage-independent colonies in dose-dependent manners; the frequencies of anchorage-independent colonies induced by these metals were similar to those induced by N-methyl-N'-nitro-N-nitrosoguanidine at approximately equal cytotoxic dose ranges (30-10% survival). 3-Aminotriazole at non-cytotoxic dosages decreased catalase activity by >80%, and markedly enhanced cadmium-induced cytotoxicity and anchorage-independent colonies. Cadmium uptake by human fibroblasts was not affected by 3-aminotriazole co-administered with 10 microM of cadmium; whereas cadmium uptake and accumulation were enhanced 1.5-fold by 3-aminotriazole co-administered with 1-2.5 microM of cadmium. Lead-induced anchorage-independence or cytotoxicity was not affected by 3-aminotriazole co-treatment; however, 3-aminotriazole did significantly enhance lead uptake and accumulation in human fibroblasts. Neither cadmium- nor lead-induced 6-thioguanine-resistant mutation frequency in human fibroblasts. Co-administering these metals with 3-aminotriazole did not enhance mutations in human fibroblasts. These results suggest that cadmium and lead may both act as tumour promoters in diploid human fibroblasts, and that reactive oxygen species is more important in cadmium- than lead-induced cytotoxicity and anchorage-independence.

Amitrole↗

PubMed1986

Cytotoxicity, cellular transformation and DNA adducts in normal human diploid fibroblasts exposed to 1-nitrosopyrene, a reduced derivative of the environmental contaminant, 1-nitropyrene.

Treatment of normal human diploid fibroblasts with 0.3-22 microM 1-nitrosopyrene resulted in a dose-dependent decrease in relative cloning efficiency and an increase in anchorage-independent growth in soft agar. When compared to previous experiments, 1-nitrosopyrene was 10- to 20-fold more cytotoxic and 5- to 10-fold more potent at inducing morphological transformation than 1-nitropyrene. Incubation of the fibroblasts with 8 microM 1-nitropyrene in the presence of xanthine oxidase, a mammalian nitroreductase, resulted in the formation of one major DNA adduct, N-(deoxyguanosin-8-yl)-1-aminopyrene, at a level of 1.1 adducts per 10(6) nucleotides. Fibroblasts treated with 1-nitrosopyrene formed the same DNA adduct; however, only a 0.3 microM concentration was required to give 0.7 adducts per 10(6) nucleotides in the fibroblast DNA. These data indicate that a limiting step in the cellular toxicity and transformation of normal human diploid fibroblasts by 1-nitropyrene is the initial reduction to 1-nitrosopyrene.

Cell Survival↗

PubMed1995

Quantitative genetics of 4x-2x hybrid populations with first-division restitution and second-division restitution 2n gametes produced by diploid parents.

A model is proposed to describe the genetic value of 4x-2x hybrids resulting from crosses between tetraploid genitors and diploid genitors that produce 2n gametes. The model takes into account the genetic consequences of the First Division Restitution (FDR) and Second Division Restitution (SDR) meiosis, particularly on the homozygosity level that 2n gametes contribute to 4x-2x hybrids. As genes can be identical by descent, numerous parameters are needed in the classical approach to describe the inbreeding effects on the mean and variance of 4x-2x hybrids. Using the concept of test value, the model allows a large decrease in the number of required parameters. The model gives the components of genetic variance and usual covariances between relatives using these synthetic parameters. The model is then used to study the efficiency of a recurrent breeding scheme to improve diploid genitors for their combining ability with tetraploid genitors. It appears that, in presence of dominance, ignoring the meiosis pattern will lead to an overestimation of additive variance and then of genetic advance. Some genetic considerations on the differences between FDR and SDR mechanisms lead us to suggest an experimental comparison of their respective advantages and disadvantages for the type of considered recurrent selection. An experimental crossing design is proposed to obtain estimates of the genetic parameters needed for this comparison.

Crosses, Genetic↗

PubMed1996

Gametophyte genetics in Zea mays L.: dominance of a restoration-of-fertility allele (Rf3) in diploid pollen.

In Zea mays L. plants carrying the S-type of sterility-inducing cytoplasm, male fertility is determined by a gametophytic, nuclear restoration-of-fertility gene. Haploid pollen carrying the fertility-restoring allele (historically designated Rf3) is starch-filled and functional, whereas pollen carrying the nonrestoring allele (historically designated rf3) is shrunken and nonfunctional. Because restoration of fertility occurs in haploid tissue, the dominance relationship of restoring and nonrestoring alleles is unknown. We have tested the dominance relationship of the restoring and nonrestoring alleles at the rf3 locus in diploid pollen. The meiotic mutant elongate was used to generate tetraploid plants carrying both Rf3 and rf3 alleles in the S cytoplasm. These plants shed predominantly starch-filled pollen, consistent with dominance of the restoring allele. Restriction fragment length polymorphisms linked to the rf3 locus demonstrated cotransmission of rf3 and Rf3 alleles through heterozygous diploid pollen, providing conclusive genetic evidence that the restoring allele is the dominant or functional form of this restoration-of-fertility gene. We suggest that other S-cytoplasm restorers result from loss-of-function mutations and propose analysis of unreduced gametes as a test of this model.

Alleles↗

PubMed1996

Escape from het-6 incompatibility in Neurospora crassa partial diploids involves preferential deletion within the ectopic segment.

Self-incompatible het-6OR/het-6PA partial diploids of Neurospora crassa were selected from a cross involving the translocation strain, T(IIL-->IIIR)AR18, and a normal sequence strain. About 25% of the partial diploids exhibited a marked increase in growth rate after 2 weeks, indicating that "escape" from het-6 incompatibility had occurred. Near isogenic tester strains with different alleles (het-6OR and het-6PA) were constructed and used to determine that 80 of 96 escape strains tested were het-6PA, retaining the het-6 allele found in the normal-sequence LGII position; 16 were het-6OR, retaining the allele in the translocated position. Restriction fragment length polymorphisms in 45 escape strains were examined with probes made from cosmids that spanned the translocated region. Along with electrophoretic analysis of chromosomes from three escape strains, RFLPs showed that escape is associated with deletion of part of one or the other of the duplicated DNA segments. Deletions ranged in size from approximately 70 kbp up to putatively the entire 270-kbp translocated region but always included a 35-kbp region wherein we hypothesize het-6 is located. The deletion spectrum at het-6 thus resembles other cases where mitotic deletions occur such as of tumor suppressor genes and of the hprt gene (coding for hypoxanthine-guanine phosphoribosyl-transferase) in humans.

Chromosome Walking↗

PubMed1998

Detailed alignment of saccharum and sorghum chromosomes: comparative organization of closely related diploid and polyploid genomes.

The complex polyploid genomes of three Saccharum species have been aligned with the compact diploid genome of Sorghum (2n = 2x = 20). A set of 428 DNA probes from different Poaceae (grasses) detected 2460 loci in F1 progeny of the crosses Saccharum officinarum Green German x S. spontaneum IND 81-146, and S. spontaneum PIN 84-1 x S. officinarum Muntok Java. Thirty-one DNA probes detected 226 loci in S. officinarum LA Purple x S. robustum Molokai 5829. Genetic maps of the six Saccharum genotypes, including up to 72 linkage groups, were assembled into "homologous groups" based on parallel arrangements of duplicated loci. About 84% of the loci mapped by 242 common probes were homologous between Saccharum and Sorghum. Only one interchromosomal and two intrachromosomal rearrangements differentiated both S. officinarum and S. spontaneum from Sorghum, but 11 additional cases of chromosome structural polymorphism were found within Saccharum. Diploidization was advanced in S. robustum, incipient in S. officinarum, and absent in S. spontaneum, consistent with biogeographic data suggesting that S. robustum is the ancestor of S. officinarum, but raising new questions about the antiquity of S. spontaneum. The densely mapped Sorghum genome will be a valuable tool in ongoing molecular analysis of the complex Saccharum genome.

DNA, Plant↗

PubMed2000

Zygotic associations and multilocus statistics in a nonequilibrium diploid population.

The usual approach to characterizing and estimating multilocus associations in a diploid population assumes that the population is in Hardy-Weinberg equilibrium. The purpose of this study is to develop a set of summary statistics that can be used to characterize and estimate the multilocus associations in a nonequilibrium population. The concept of "zygotic associations" is first expanded to facilitate the development. The summary statistics are calculated using the distribution of a random variable, the number of heterozygous loci (K) found in diploid individuals in the population. In particular, the variance of K consists of single-locus and multilocus components with the latter being the sum of zygotic associations between pairs of loci. Simulation results show that the multilocus associations in the variance of K are detectable in a sample of moderate size (> or =30) when the sum of all pairwise zygotic associations is greater than zero and when gene frequency is intermediate. The method presented here is a generalization of the well-known development for the Hardy-Weinberg equilibrium population and thus may be of more general use in elucidating the multilocus organizations in nonequilibrium and equilibrium populations.

Analysis of Variance↗

PubMed2000

Copy number lability and evolutionary dynamics of the Adh gene family in diploid and tetraploid cotton (Gossypium).

Nuclear-encoded genes exist in families of various sizes. To further our understanding of the evolutionary dynamics of nuclear gene families we present a characterization of the structure and evolution of the alcohol dehydrogenase (Adh) gene family in diploid and tetraploid members of the cotton genus (Gossypium, Malvaceae). A PCR-based approach was employed to isolate and sequence multiple Adh gene family members, and Southern hybridization analyses were used to document variation in gene copy number. Adh gene copy number varies among Gossypium species, with diploids containing at least seven Adh loci in two primary gene lineages. Allotetraploid Gossypium species are inferred to contain at least 14 loci. Intron lengths vary markedly between loci, and one locus has lost two introns usually found in other plant Adh genes. Multiple examples of apparent gene duplication events were observed and at least one case of pseudogenization and one case of gene elimination were also found. Thus, Adh gene family structure is dynamic within this single plant genus. Evolutionary rate estimates differ between loci and in some cases between organismal lineages at the same locus. We suggest that dynamic fluctuation in copy number will prove common for nuclear genes, and we discuss the implications of this perspective for inferences of orthology and functional evolution.

Alcohol Dehydrogenase↗

PubMed2002

Structural analysis of aberrant chromosomes that occur spontaneously in diploid Saccharomyces cerevisiae: retrotransposon Ty1 plays a crucial role in chromosomal rearrangements.

The structural analysis of aberrant chromosomes is important for our understanding of the molecular mechanisms underlying chromosomal rearrangements. We have identified a number of diploid Saccharomyces cerevisiae clones that have undergone loss of heterozygosity (LOH) leading to functional inactivation of the hemizygous URA3 marker placed on the right arm of chromosome III. Aberrant-sized chromosomes derived from chromosome III were detected in approximately 8% of LOH clones. Here, we have analyzed the structure of the aberrant chromosomes in 45 LOH clones with a PCR-based method that determines the ploidy of a series of loci on chromosome III. The alterations included various deletions and amplifications. Sequencing of the junctions revealed that all the breakpoints had been made within repeat sequences in the yeast genome, namely, MAT-HMR, which resulted in intrachromosomal deletion, and retrotransposon Ty1 elements, which were involved in various translocations. Although the translocations involved different breakpoints on different chromosomes, all breakpoints were exclusively within Ty1 elements. Some of the resulting Ty1 elements left at the breakpoints had a complex construction that indicated the involvement of other Ty1 elements not present at the parental breakpoints. These indicate that Ty1 elements are crucially involved in the generation of chromosomal rearrangements in diploid yeast cells.

Chromosome Aberrations↗

PubMed2003

Partial diploidization of meiosis in autotetraploid Arabidopsis thaliana.

Meiosis was analyzed cytogenetically in autotetraploids of Arabidopsis, including both established lines and newly generated autotetraploid plants. Fluorescent in situ hybridization with 5S and 45S rDNA probes was used to identify the different chromosomes at metaphase I of meiosis. Multivalents were observed frequently in all the lines analyzed, but there were significant differences in multivalent frequency not only between the newly generated tetraploids and the established lines but also among the different established lines. The new tetraploids showed high multivalent frequencies, exceeding the theoretical 66.66% predicted by the simple random-end pairing model, in some cases significantly, thus indicating that Arabidopsis autotetraploids have more than two autonomous pairing sites per chromosome, despite their small sizes. The established lines showed fewer multivalents than the new autotetraploids did, but the extent of this reduction was strongly line and chromosome dependent. One line in particular showed a large reduction in multivalents and a concomitant increase in bivalents, while the other lines showed lesser reductions in multivalents. The reduction in multivalents was not uniformly distributed across chromosomes. The smaller chromosomes, especially chromosomes 2 and 4, showed the most marked reductions while the largest chromosome (1) showed virtually no reduction compared to the new tetraploids. It is concluded that the established autotetraploid lines have undergone a partial diploidization of meiosis, but not necessarily genetical diploidization, since their creation. Possible mechanisms for the resulting change in meiotic chromosome behavior are discussed.

Arabidopsis↗

PubMed1976

Diploid gynogenesis in the Mexican axolotl.

Gynogenetic diploid axolotls were produced by activating eggs with ultraviolet-inactivated sperm, and then subjecting the activated eggs to heat shock. Optimal conditions for ultraviolet inactivation of the sperm, and for suppression of the second meiotic division by heat shock, were established. Gynogenetic diploids produced by these procedures included progeny homozygous for recessive alleles carried by a heterozygous mother. Gynogenesis could, therefore, be used to uncover new mutations more rapidly than by conventional inbreeding techniques. However, some difficulty was encountered in recognizing mutant phenotypes because of the high incidence of abnormalities and deaths. Defective embryos probably resulted from a combination of heat-shock-induced damage to the eggs and the expression of deleterious recessive alleles carried by the mother.

Ambystoma↗

PubMed1980

On the evolution of new metabolic functions in diploid organisms.

Evolution of lactose utilization via the ebg system of Escherichia coli requires both structural gene (ebgA) and regulatory gene (ebgR) mutations. Because evolution of new metabolic functions in diploids might be subject to constraints not present in haploid organisms, merodiploid strains carrying a wild-type and an evolved ebgA allele, or a wild-type and an evolved ebgR allele were constructed. I show that heterozygosity at ebgA does not significantly affect the selective advantage of the evolved ebgA allele; whereas heterozygosity at ebgR eliminates the selective advantage of the evolved ebgR allele. Is is suggested that, in diploid organisms, evolution of new functions for systems under negative control would be very difficult.

Biological Evolution↗

PubMed1980

Diploid spore formation and other meiotic effects of two cell-division-cycle mutations of Saccharomyces cerevisiae.

The meiotic effects of two cell-division-cycle mutations of Saccharomyces cerevisiae (cdc5 and cdc14) have been examined. These mutations were isolated by L.H. HARTWELL and his colleagues and characterized as defective in mitosis, causing a temperature-sensitive arrest in late nuclear division. When subjected to the restrictive temperature in meiosis, diploid cells homozygous for either of these mutations generally proceeded through premeiotic DNA synthesis and commitment to meiotic levels of recombination, but then arrested at a stage following spindle pole body (SPB) duplication and separation. The two SPBs lacked the interconnection by spindle microtubules typical of the complete meiosis I spindle. Challenge of these homozygotes by a semi-restrictive temperature often caused the production of asci containing two diploid spores. Genetic analysis of the viable pairs of spores revealed that each spore had become homozygous for centromere-linked markers significantly more frequently than for distal markers, indicating that the two spores each contained pairs of sister centromeres that had co-segregated in the reductional division of meiosis I. Ultrastructural analysis of the cdc5 homozygote demonstrated that these cells had completed meiosis I and formed two meiosis II spindles, but that the latter remained unusually short. This resulted in the encapsulation of both poles of each spindle within a single spore wall. These mutations therefore are defective in both meiotic divisions, as well as in the mitotic division described originally.

Cell Cycle↗

PubMed2005

Effects of human Na(+)/dicarboxylate cotransporter 3 on the replicative senescence of human embryonic lung diploid fibroblasts.

To investigate the role of human Na(+)/dicarboxylate cotransporter 3 (hNaDC3) in the replicative senescence of normal human embryonic lung diploid fibroblasts (WI-38), a retroviral vector containing hNaDC3 was constructed. hNaDC3 was introduced into normal WI-38 cells through infection with the retroviral virus. Monoclones were selected with G418. The integration and expression of exotic genes were confirmed by Northern blot and Western blot. When compared with the control cells, WI-38 cells transfected with hNaDC3 cDNA showed significant suppression of growth rate (by 40%), increase of positive rate of SA-beta-gal staining, decrease of mitochondrial membrane potential, shortening of telomere length, and increase of P16 and P21 expression. The morphology characteristics of senescent fibroblasts appeared earlier. Our results have, for the first time, demonstrated that high expression of hNaDC3 may be able to, at least partly, promote the cellular senescence of human diploid fibroblasts.

Blotting, Northern↗

PubMed1981

X-linked processes in serially passaged "aging" human diploid cells.

Human diploid fibroblasts serially cultured in vitro show a progressive decline in their proliferative capacity. Much before the cells cease to divide, changes in certain phenotypic parameters can also be detected with passage level. A progressive decline in the ratio of two enzyme activities in the purine salvage pathway, one an X-linked enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGPRT) and the other a biochemically related autosomal-linked enzyme, adenine phosphoribosyltransferase (APRT) becomes apparent with increasing population doublings. The more extensive relative decline in HGPRT activity with passage may be explained on gene dosage effects subsequent to the random inactivation of one X-chromosome in the somatic cells of mammalian females; however, other interpretations can be considered. Since the enzyme activity ratio of HGPRT/APRT decreases linearly with population doubling, it could be useful for the evaluation of the biological "age" of serially passaged cultures. Studies of X-linked processes in human diploid cells and its variations during the life-span in culture may contribute to our understanding of some of the mechanisms of "senescence/change" and of the etiology of certain maturity onset disorders.

Adenine Phosphoribosyltransferase↗

PubMedDate not supplied

Karyotypic analysis of N-banded chromosomes of diploid alfalfa: Medicago sativa ssp. caerulea and ssp. falcata and their hybrid.

Chromosomes of two diploid (2n = 2x = 16) subspecies of Medicago sativa, ssp. caerulea and ssp. falcata, and their hybrid were studied using an N-banding technique. This study was undertaken to develop an N-banded karyotype of ssp. caerulea and ssp. falcata, and determine if the same technique could be used to identify parental chromosomes in hybrids. The chromosomes of ssp. falcata have only centromeric N bands and thus individual chromosomes could not be identified. However, chromosome-specific bands were observed in ssp. caerulea enabling the identification of each of the eight pairs of chromosomes and the development of an idiogram. All chromosomes have a centromeric band and a telomeric band in the short arm. All of the chromosomes, except chromosomes 7 and 8, have interstitial bands in their long arms and chromosome 5 has two faint interstitial bands in its long arm. The satellited chromosome is easily distinguished due to the secondary constriction and characteristic band at the nucleolar organizer region. The differences in banding patterns between these subspecies makes it possible to distinguish chromosomes from each other in their hybrids. This is the first report of the use of N banding to identify the diploid chromosomes of M. sativa ssp. caerulea and ssp. falcata.

Centromere↗