SELECTION PRESSURE IN CELL POPULATIONS OF VICIA HAJASTANA CULTURED IN VITRO

1972 ◽  
Vol 14 (1) ◽  
pp. 65-70 ◽  
Author(s):  
B. D. Singh ◽  
B. L. Harvey ◽  
K. N. Kao ◽  
R. A. Miller
Keyword(s):  
Frequency Distribution ◽  
Selection Pressure ◽  
Low Frequency ◽  
Cell Populations ◽  
Tissue Cultures ◽  
Very Low Frequency ◽  
Selection For ◽  
Diploid Cells ◽  
Mature Seeds

Tissue cultures from mature seeds of Vicia hajastana Grossh (2n = 10) were maintained in liquid B5 medium with 4.5 × 10−6 M 2,4-D. Initially the cultures had a very low frequency of diploid cells, which increased to 91.7% after 295 days in culture, indicating a strong selection for diploid cells. Chromosomes with changed morphology were observed and anaphase analysis showed various abnormalities. The frequency distribution of different chromosomes of the genome in aneuploid cells was nonrandom.

Improvement of effectiveness in maize breeding

2006 ◽  
Vol 54 (3) ◽  
pp. 351-358 ◽  
Author(s):  
P. Pepó
Keyword(s):  
Recurrent Selection ◽  
Genetic Manipulation ◽  
Field Testing ◽  
Tissue Cultures ◽  
Maize Breeding ◽  
Breeding Programmes ◽  
Speed Up ◽  
Selection For

Plant regeneration via tissue culture is becoming increasingly more common in monocots such as maize (Zea mays L.). Pollen (gametophytic) selection for resistance to aflatoxin in maize can greatly facilitate recurrent selection and the screening of germplasm for resistance at much less cost and in a shorter time than field testing. In vivo and in vitro techniques have been integrated in maize breeding programmes to obtain desirable agronomic attributes, enhance the genes responsible for them and speed up the breeding process. The efficiency of anther and tissue cultures in maize and wheat has reached the stage where they can be used in breeding programmes to some extent and many new cultivars produced by genetic manipulation have now reached the market.

scholarly journals Transposition of Tn1213Encoding the PER-1 Extended-Spectrum β-Lactamase

2018 ◽  
Vol 62 (3) ◽  
pp. e02453-17 ◽  
Author(s):  
Stefano Mancini ◽  
Laurent Poirel ◽  
Nicolas Kieffer ◽  
Patrice Nordmann
Keyword(s):  
Escherichia Coli ◽  
Low Frequency ◽  
Insertion Sequences ◽  
Content Type ◽  
Very Low Frequency ◽  
Extended Spectrum

ABSTRACTPER-1 is an extended-spectrum β-lactamase that is encoded by a gene located in composite transposon Tn1213made by two distinct insertion sequences, namely, ISPa12and ISPa13. In vitromobilization performed inEscherichia colishows that Tn1213is functional and is able to mobilize theblaPER-1gene, although at a very low frequency (ca. 1 × 10−9).

CHANGES IN CHROMOSOME NUMBER IN MICROSPORE CALLUS OF RICE DURING SUCCESSIVE SUBCULTURES

1980 ◽  
Vol 22 (4) ◽  
pp. 607-614 ◽  
Author(s):  
Chi-Chang Chen ◽  
Chung-Mong Chen
Keyword(s):  
Chromosome Doubling ◽  
Oryza Sativa L ◽  
Callus Cultures ◽  
Microspore Development ◽  
Cell Type ◽  
Ploidy Levels ◽  
Two Cultures ◽  
Selection For ◽  
Diploid Cells

Forty-six callus cultures of rice (Oryza sativa L., 2n = 24), each presumably originating from a single microspore, were established and maintained on a medium containing 2,4-D. At the end of the first transfer 24% of the cultures were nonhaploid consisting of only diploid or polyploid cells, or of cells of two ploidy levels. Nuclear fusion and endomitosis occurring during the initial stages of in vitro microspore development were postulated to account for the formation of nonhaploid callus. Seventeen cultures were studied cytologically through 19 transfers. Only in one tetraploid and one hexaploid callus did the ploidy levels of cells remain unchanged during culture. Chromosome numbers in 13 cultures fell into a geometric series. Since no diplo- and quadruplochromosomes were observed, it was inferred that endomitosis rather than endoreduplication was responsible for the changes. In spite of the tendency for chromosome doubling, the proportions of cells of different ploidy levels were fixed in the 13 cultures at later transfers. Haploid cells were eliminated from all cultures. Diploid cells became predominant in eight cultures and tetraploid cells in five, suggesting a selection for either cell type. Triploids appeared in two cultures which initially did not contain this type of cell. Limited cytological information indicated that triploid cells might have originated from tetraploid cells through reductional grouping of chromosomes accompanied by multipolar formation.

scholarly journals Impact of Therapeutic Treatment with β-Lactam on Transfer of the blaCTX-M-9 Resistance Gene from Salmonella enterica Serovar Virchow to Escherichia coli in Gnotobiotic Rats

2009 ◽  
Vol 75 (17) ◽  
pp. 5523-5528 ◽  
Author(s):  
St�phanie Faure ◽  
Agn�s Perrin-Guyomard ◽  
Jean-Michel Delmas ◽  
Michel Laurentie
Keyword(s):  
Escherichia Coli ◽  
Salmonella Enterica ◽  
Transfer Rate ◽  
Selective Pressure ◽  
Low Frequency ◽  
E Coli ◽  
Chicken Farm ◽  
Selection For ◽  
Therapeutic Doses

ABSTRACT The conjugative transfer of the plasmid carrying the bla CTX-M-9 gene from Salmonella enterica serovar Virchow isolated from a chicken farm to a recipient Escherichia coli strain was evaluated in vitro and in axenic rats inoculated with both strains, with or without selective pressure due to therapeutic doses of cefixime. The transfer of the bla CTX-M-9 gene of S. enterica serovar Virchow to E. coli was confirmed in vitro, at a low frequency of 5.9 � 10−8 transconjugants/donors. This transfer rate was higher in gnotobiotic rats and reached ∼10−5 transconjugants/donors without selective pressure. This frequency was not affected by the addition of therapeutic doses of cefixime. Thus, estimates of in vitro transfer underestimated potential transfer in the digestive tract, and therapeutic doses of cefixime did not increase the selection for transconjugants.

scholarly journals Spontaneous polyploids and antimutators compete during the evolution of mutator cells

2019 ◽  
Author(s):  
Maxwell A. Tracy ◽  
Mitchell B. Lee ◽  
Brady L. Hearn ◽  
Ian T. Dowsett ◽  
Luke C. Thurber ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Dna Polymerase ◽  
Selection Pressure ◽  
Low Frequency ◽  
Cell Populations ◽  
Mutator Phenotype ◽  
Mutation Burden ◽  
Mutator Allele ◽  
Homozygous Mutations ◽  
Biallelic Mutations

AbstractHeterozygous mutations affecting DNA polymerase (Pol) exonuclease domains and homozygous inactivation of mismatch repair (MMR) each generate “mutator” phenotypes capable of driving tumorigenesis. Cancers with both defects exhibit an explosive increase in mutation burden that appears to reach a threshold, consistent with selection acting against further mutation accumulation. In haploid yeast, simultaneous defects in polymerase proofreading and MMR select for “antimutator” mutants that suppress the mutator phenotype. We report here that spontaneous polyploids also escape this “error-induced extinction” and routinely out-compete antimutators in evolved haploid cultures. We performed similar experiments to explore how diploid yeast adapt to the mutator phenotype. We first evolved cells with homozygous mutations affecting proofreading and MMR, which we anticipated would favor tetraploid emergence. While tetraploids arose with a low frequency, in most cultures, a single antimutator clone rose to prominence carrying biallelic mutations affecting the polymerase mutator alleles. Variation in mutation rate between subclones from the same culture suggests there exists continued selection pressure for additional antimutator alleles. We then evolved diploid yeast modeling MMR-deficient cancers with the most common heterozygous exonuclease domain mutation (POLE-P286R). Although these cells grew robustly, within 120 generations, all subclones carried truncating or nonsynonymous mutations in the POLE-P286R homologous allele (pol2-P301R) that suppressed the mutator phenotype as much as 100-fold. Independent adaptive events in the same culture were common. Our findings suggest that analogous tumor cell populations may adapt to the threat of extinction by polyclonal mutations that neutralize the POLE mutator allele and preserve intra-tumoral genetic diversity for future adaptation.

Gametic selection during wheat anther culture

Genome ◽  
1989 ◽  
Vol 32 (1) ◽  
pp. 54-56 ◽  
Author(s):  
J. De Buyser ◽  
B. Bachelier ◽  
Y. Henry
Keyword(s):  
Anther Culture ◽  
Selection Pressure ◽  
Pollen Grains ◽  
In Vitro Cultures ◽  
Male Gametes ◽  
Different Types ◽  
Selection For ◽  
Gametic Selection ◽  
Biased Samples

Gametic selection was investigated in a monosomic 1D line of wheat. Comparison of chromosome numbers in progenies from cross- or self-pollination and anther culture indicated the frequency of the different types of gametes acting in zygote formation. The progenies obtained from reciprocal crosses (monosomic × euploid) were different in terms of frequencies of monosomic plants. All the pollen grains do not have an equal probability of fertilization since a strong gametic selection for euhaploid male gametes was observed when the monosomic line was used as male parent; only 13% of the nullisomic survived to embryogenesis and seed germination. Regenerants from anther culture also demonstrated that the percentage of nullihaploids was reduced, indicating a strong selection for euhaploid gametes. A comparison between the frequency of male nullihaploid gametes in the cross disomic × monosomic and in the anther culture revealed that the two processes generate the same gamete transmission. The in vitro cultures do not induce more selection pressure than the embryogenic development even if they are together biased samples of the male gametic population.

scholarly journals Selection for an invariant Character, Vibrissa Number, in the House Mouse III. Correlated Responses

1962 ◽  
Vol 15 (1) ◽  
pp. 188 ◽  
Author(s):  
AS Fraser ◽  
BM Kindred
Keyword(s):  
House Mouse ◽  
Low Frequency ◽  
Mutant Mice ◽  
Selection Experiment ◽  
Correlated Responses ◽  
Very Low Frequency ◽  
Selection For

Selection for increased and decreased total number of secondary vibrissae has been practised on the mutant mice of a stock in which the tabby gene is segregating. Five separate groups of vibrissae contribute to the total number and differences were found in the response of individual groups of vibrissae to selection. These differences occur both in the main selection experiment and in subsidiary experi-ments based on rare non-tabby mice with abnormal scores which occur with very low frequency in ordinary mouse stocks.

scholarly journals Spontaneous Polyploids and Antimutators Compete During the Evolution of Saccharomyces cerevisiae Mutator Cells

Genetics ◽  
2020 ◽  
Vol 215 (4) ◽  
pp. 959-974 ◽  
Author(s):  
Maxwell A. Tracy ◽  
Mitchell B. Lee ◽  
Brady L. Hearn ◽  
Ian T. Dowsett ◽  
Luke C. Thurber ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Dna Polymerase ◽  
Selection Pressure ◽  
Low Frequency ◽  
Cell Populations ◽  
Mutator Phenotype ◽  
Mutation Burden ◽  
Mutator Allele ◽  
Homozygous Mutations ◽  
Biallelic Mutations

Mutations affecting DNA polymerase exonuclease domains or mismatch repair (MMR) generate “mutator” phenotypes capable of driving tumorigenesis. Cancers with both defects exhibit an explosive increase in mutation burden that appears to reach a threshold, consistent with selection acting against further mutation accumulation. In Saccharomyces cerevisiae haploid yeast, simultaneous defects in polymerase proofreading and MMR select for “antimutator” mutants that suppress the mutator phenotype. We report here that spontaneous polyploids also escape this “error-induced extinction” and routinely outcompete antimutators in evolved haploid cultures. We performed similar experiments to explore how diploid yeast adapt to the mutator phenotype. We first evolved cells with homozygous mutations affecting polymerase δ proofreading and MMR, which we anticipated would favor tetraploid emergence. While tetraploids arose with a low frequency, in most cultures, a single antimutator clone rose to prominence carrying biallelic mutations affecting the polymerase mutator alleles. Variation in mutation rate between subclones from the same culture suggests that there exists continued selection pressure for additional antimutator alleles. We then evolved diploid yeast modeling MMR-deficient cancers with the most common heterozygous exonuclease domain mutation (POLE-P286R). Although these cells grew robustly, within 120 generations, all subclones carried truncating or nonsynonymous mutations in the POLE-P286R homologous allele (pol2-P301R) that suppressed the mutator phenotype as much as 100-fold. Independent adaptive events in the same culture were common. Our findings suggest that analogous tumor cell populations may adapt to the threat of extinction by polyclonal mutations that neutralize the POLE mutator allele and preserve intratumoral genetic diversity for future adaptation.

The Attenuation of Very Low Frequency Brain Oscillations in Transitions from a Rest State to Active Attention

2009 ◽  
Vol 23 (4) ◽  
pp. 191-198 ◽  
Author(s):  
Suzannah K. Helps ◽  
Samantha J. Broyd ◽  
Christopher J. James ◽  
Anke Karl ◽  
Edmund J. S. Sonuga-Barke
Keyword(s):  
Brain Activity ◽  
Sampling Rate ◽  
Low Frequency ◽  
Future Research ◽  
Adhd Symptoms ◽  
Default Mode ◽  
Very Low Frequency ◽  
Wide Range ◽  
Interference Hypothesis ◽  
Mode Interference

Background: The default mode interference hypothesis ( Sonuga-Barke & Castellanos, 2007 ) predicts (1) the attenuation of very low frequency oscillations (VLFO; e.g., .05 Hz) in brain activity within the default mode network during the transition from rest to task, and (2) that failures to attenuate in this way will lead to an increased likelihood of periodic attention lapses that are synchronized to the VLFO pattern. Here, we tested these predictions using DC-EEG recordings within and outside of a previously identified network of electrode locations hypothesized to reflect DMN activity (i.e., S3 network; Helps et al., 2008 ). Method: 24 young adults (mean age 22.3 years; 8 male), sampled to include a wide range of ADHD symptoms, took part in a study of rest to task transitions. Two conditions were compared: 5 min of rest (eyes open) and a 10-min simple 2-choice RT task with a relatively high sampling rate (ISI 1 s). DC-EEG was recorded during both conditions, and the low-frequency spectrum was decomposed and measures of the power within specific bands extracted. Results: Shift from rest to task led to an attenuation of VLFO activity within the S3 network which was inversely associated with ADHD symptoms. RT during task also showed a VLFO signature. During task there was a small but significant degree of synchronization between EEG and RT in the VLFO band. Attenuators showed a lower degree of synchrony than nonattenuators. Discussion: The results provide some initial EEG-based support for the default mode interference hypothesis and suggest that failure to attenuate VLFO in the S3 network is associated with higher synchrony between low-frequency brain activity and RT fluctuations during a simple RT task. Although significant, the effects were small and future research should employ tasks with a higher sampling rate to increase the possibility of extracting robust and stable signals.

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