scholarly journals How Barbara McClintock discovered transposable elements in maize

2012 ◽  
Vol 10 (4) ◽  
pp. 3-13
Author(s):  
Keyword(s):  
Transposable Elements ◽  
Chromosomal Location ◽  
Chromosome Breakage ◽  
Dna Transposons ◽  
Barbara Mcclintock ◽  
Controlling Elements ◽  
Earthquake Event ◽  
Maize Kernels ◽  
The Relationship

The paper describes the early part of Barbara McClintock`s work on DNA transposons in maize, in which she discovered the Ac-Ds family of mobile "controlling elements". An account is first given of the cytology of the system that was used to generate intact chromosomes having "sticky" (broken) ends. Cytogenetical aspects of the chromatid and chromosome breakage-fusion-bridge cycles, deriving from breakage, are then described, which leads on to the way in which variegation in phenotypes of the maize kernels could be "read" in terms of chromosome breakage. The "genetic earthquake" event of 1944, triggered by introducing broken chromosomes into a zygote from both parents, lead to the discovery of Ds and Ac. Finding mobility of Ds from one chromosomal location to another was pure serendipity: the transposition showed itself while experiments were being undertaken to accurately map Ds. A similar chance observation revealed transposition of Ac as well, and then the relationship between the two elements was elucidated in terms of their autonomous and non-autonomous nature.

scholarly journals Chromosome breakage undetectable in active Mu lines of maize.

Genetics ◽  
1989 ◽  
Vol 122 (1) ◽  
pp. 205-209
Author(s):  
L J Rowland ◽  
D S Robertson ◽  
J Strommer
Keyword(s):  
Transposable Elements ◽  
Low Frequency ◽  
Chromosome Breakage ◽  
Very Low Frequency ◽  
Induced Mutants ◽  
Simultaneous Loss

Abstract We have used a set of Mutator-induced mutants of Bz1 to test whether members of the Mutator (Mu) family of maize transposable elements produce broken chromosomes. From our inability to demonstrate the simultaneous loss of two dominant endosperm markers distal to Mu insertions at Bz1 we conclude that either Mu, unlike many elements of the Ds family, does not induce such breaks, or it does so at a very low frequency.

The Date and Circumstances of Olympiodorus of Thebes

Traditio ◽  
1993 ◽  
Vol 48 ◽  
pp. 1-29 ◽  
Author(s):  
Andrew Gillett
Keyword(s):  
Roman Empire ◽  
Late Antiquity ◽  
Fifth Century ◽  
Imperial Court ◽  
Political Narrative ◽  
History Of ◽  
The Rich ◽  
The Relationship ◽  
Western Half

Olympiodorus of Thebes is an important figure for the history of late antiquity. The few details of his life preserved as anecdotes in hisHistorygive glimpses of a career which embraced the skills of poet, philosopher, and diplomat. A native of Egypt, he had influence at the imperial court of Constantinople, among the sophists of Athens, and even outside the borders of the empire. HisHistory(more correctly, his “materials for history”) is lost, surviving only as fragments in the narratives of Zosimus, Sozomen, and Philostorgius, and in the rich summary given by the ninth-century Byzantine patriarch Photius. These remains comprise the most substantial narrative sources for events in the western Roman Empire in the early fifth century. Besides its value as a source, theHistoryis important as a monument to the vitality of the belief in the unity of the Roman Empire under the Theodosian dynasty. Olympiodorus wrote in Greek, and knowledge of his work is attested only in Constantinople, yet his political narrative, from 407 to 425, concerns only events in the western half of the empire. To understand the significance of these facts, it is necessary to set the composition of Olympiodorus's work in its proper context. Clarifying the date of publication is the first step toward this goal. Internal and external evidence suggests that the work was written in 440 or soon after, more than a decade later than the date of composition usually accepted. Taken with thematic emphases evident in the structure of theHistory, this revised dating explains why an eastern writer should have written a detailed account of western events in the early part of the century. Olympiodorus's account is a characteristic product of the highly literate class of eastern imperial civil servants, and of their genuine preoccupation with the relationship between the eastern and western halves of the Roman Empire at a time when both were threatened by the rise of the new Carthaginian power of the Vandals.

People and the contemporary environment

2003 ◽  
Author(s):  
Sally Eden
Keyword(s):  
Environmental Management ◽  
Twentieth Century ◽  
Academic Disciplines ◽  
Human Environment ◽  
Late Twentieth ◽  
Catch Up ◽  
Ecological Science ◽  
The Relationship ◽  
Late Twentieth Century

Geographical approaches to human-environment relations have been diverse and dynamic over the last century. They have also been heavily influenced not only by academic disciplines outside geography but by popular and policy concerns outside academia. From an initial flurry of activity about how the environment influences society in the early part of the century, British geography then took a detour to other topics even as other disciplines discovered the environment as a topic of interest. This left geographers playing ‘catch-up’ in the late twentieth century, as the discipline sought to reoccupy the ground previously abandoned. This is not over yet: in the 1990s, research into ‘the environment’ and ‘nature’ was scattered across academia. This chapter examines the relationship between humans and the contemporary environment, focusing on environmental protection, environmental management and ecological science, environmental policy and management, environmentalism, and environment and history.

scholarly journals Impact of Transposable Elements on Methylation and Gene Expression across Natural Accessions of Brachypodium distachyon

2020 ◽  
Vol 12 (11) ◽  
pp. 1994-2001 ◽  
Author(s):  
Michele Wyler ◽  
Christoph Stritt ◽  
Jean-Claude Walser ◽  
Célia Baroux ◽  
Anne C Roulin
Keyword(s):  
Gene Expression ◽  
Dna Methylation ◽  
Transposable Elements ◽  
Brachypodium Distachyon ◽  
Large Fraction ◽  
Expression Patterns ◽  
Specific Gene ◽  
Differential Gene ◽  
The Relationship ◽  
Silent State

Abstract Transposable elements (TEs) constitute a large fraction of plant genomes and are mostly present in a transcriptionally silent state through repressive epigenetic modifications, such as DNA methylation. TE silencing is believed to influence the regulation of adjacent genes, possibly as DNA methylation spreads away from the TE. Whether this is a general principle or a context-dependent phenomenon is still under debate, pressing for studying the relationship between TEs, DNA methylation, and nearby gene expression in additional plant species. Here, we used the grass Brachypodium distachyon as a model and produced DNA methylation and transcriptome profiles for 11 natural accessions. In contrast to what is observed in Arabidopsis thaliana, we found that TEs have a limited impact on methylation spreading and that only few TE families are associated with a low expression of their adjacent genes. Interestingly, we found that a subset of TE insertion polymorphisms is associated with differential gene expression across accessions. Thus, although not having a global impact on gene expression, distinct TE insertions may contribute to specific gene expression patterns in B. distachyon.

Measurement of the Aging of Rubber Vulcanizates

1960 ◽  
Vol 33 (2) ◽  
pp. 502-509 ◽  
Author(s):  
J. Mandel ◽  
F. L. Roth ◽  
M. N. Steel ◽  
R. D. Stiehler
Keyword(s):  
Aging Process ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Arrhenius Equation ◽  
Effective Means ◽  
Ultimate Elongation ◽  
Rubber Compounds ◽  
The Relationship

Abstract Ultimate elongation (strain at failure) can be used to assess the aging of all rubber vulcanizates. For this purpose, it appears that Equation (2) can be used to express the early part of the aging process, corresponding to a period of aging at room temperature of 10 or more years. Prediction of shelf aging from tests at two or more elevated temperatures is only possible if the relationship between aging and temperature is known. For some rubber compounds the Arrhenius equation appears to hold. In these instances, it provides an effective means for estimating shelf aging.

scholarly journals Transposons, Genome Size, and Evolutionary Insights in Animals

2015 ◽  
Vol 147 (4) ◽  
pp. 217-239 ◽  
Author(s):  
Adriana Canapa ◽  
Marco Barucca ◽  
Maria A. Biscotti ◽  
Mariko Forconi ◽  
Ettore Olmo
Keyword(s):  
Natural Selection ◽  
Transposable Elements ◽  
Genome Size ◽  
Small Rnas ◽  
Evolutionary History ◽  
Animal Species ◽  
Current Situation ◽  
Environmental Stressors ◽  
Functional Parameters ◽  
The Relationship

The relationship between genome size and the percentage of transposons in 161 animal species evidenced that variations in genome size are linked to the amplification or the contraction of transposable elements. The activity of transposable elements could represent a response to environmental stressors. Indeed, although with different trends in protostomes and deuterostomes, comprehensive changes in genome size were recorded in concomitance with particular periods of evolutionary history or adaptations to specific environments. During evolution, genome size and the presence of transposable elements have influenced structural and functional parameters of genomes and cells. Changes of these parameters have had an impact on morphological and functional characteristics of the organism on which natural selection directly acts. Therefore, the current situation represents a balance between insertion and amplification of transposons and the mechanisms responsible for their deletion or for decreasing their activity. Among the latter, methylation and the silencing action of small RNAs likely represent the most frequent mechanisms.

Fecundity of male rabbits as determined by “dummy matings”

1938 ◽  
Vol 28 (1) ◽  
pp. 122-134 ◽  
Author(s):  
C. Macirone ◽  
Arthur Walton
Keyword(s):  
Seasonal Variation ◽  
Individual Variation ◽  
Sperm Production ◽  
Sexual Stimulation ◽  
Sex Drive ◽  
Short Period ◽  
The Relationship ◽  
Average Fertility ◽  
Artificial Vagina

A method of obtaining samples of semen from rabbit males by means of a dummy and artificial vagina is described. The volume of the semen, and the number of spermatozoa per cm. (density) and the total number of spermatozoa in the sample have been measured. The data obtained from these measurements have been analysed under the following headings:1. Relation between total volume and total number of spermatozoa. With an increase in the total volume of the ejaculate there is an increase in the total number of spermatozoa, but the relationship is not linear. The density of spermatozoa varies considerably.2. Seasonal variation. Seasonal variation in sperm production is not marked in these data. There is slight tendency for the numbers to be highest in the early part of the year and lowest in August and September when the animal is moulting.3. Individual variation. In each individual, variation is considerable. Differences between individuals are not marked, but as most of the animals were of low average fertility, it is probable that this result is not typical of male rabbits in general.4. Effect of successive matings with in a short period. In successive matings the number of spermatozoa diminishes rapidly. As the density is not much affected, the diminution is due to reduction in the volume of the ejaculate.5. Relation between the number of spermatozoa in the ejaculate and the number in the various sections of the spermatic tract. After a series of samples had been obtained, some males were killed and an estimate made of the number of spermatozoa present in various parts of the tract. From the results it is concluded that on ejaculation the vas deferens is practically emptied and that some sperm in the ejaculate come from the cauda epididymis.6. Observations on sexual behaviour. The sexual pattern of the male rabbit is described and the relation between sexual stimulation and sex drive is discussed.

scholarly journals COVID-19 hospital activity and in-hospital mortality during the first and second waves of the pandemic in England: an observational study

Thorax ◽  
2021 ◽  
pp. thoraxjnl-2021-218025
Author(s):  
William K Gray ◽  
Annakan V Navaratnam ◽  
Jamie Day ◽  
Julia Wendon ◽  
Tim W R Briggs
Keyword(s):  
Hospital Mortality ◽  
Hospital Stay ◽  
Ethnic Groups ◽  
Mortality Rates ◽  
Data Set ◽  
Black African ◽  
Substantial Decline ◽  
The Relationship ◽  
Second Wave

IntroductionWe aimed to examine the profile of, and outcomes for, all people hospitalised with COVID-19 across the first and second waves of the pandemic in England.MethodsThis was an exploratory retrospective analysis of observational data from the Hospital Episode Statistics data set for England. All patients aged ≥18 years in England with a diagnosis of COVID-19 who had a hospital stay that was completed between 1 March 2020 and 31 March 2021 were included. In-hospital mortality was the primary outcome of interest. The second wave was identified as starting on 1 September 2020. Multilevel logistic regression modelling was used to investigate the relationship between mortality and demographic, comorbidity and temporal covariates.ResultsOver the 13 months, 374 244 unique patients had a diagnosis of COVID-19 during a hospital stay, of whom 93 701 (25%) died in hospital. Adjusted mortality rates fell from 40%–50% in March 2020 to 11% in August 2020 before rising to 21% in January 2021 and declining steadily to March 2021. Improvements in mortality rates were less apparent in older and comorbid patients. Although mortality rates fell for all ethnic groups from the first to the second wave, declines were less pronounced for Bangladeshi, Indian, Pakistani, other Asian and black African ethnic groups.ConclusionsThere was a substantial decline in adjusted mortality rates during the early part of the first wave which was largely maintained during the second wave. The underlying reasons for consistently higher mortality risk in some ethnic groups merits further study.

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