5 research outputs found

    Phenotypic and meiotic differences between diploid and polyploid plants

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    Polyploidy is present in a large number of crop plants and is considered as one of the driving forces in the evolution of angiosperms. Unlocking genetic variation in various autopolyploid crop plants is highly relevant to crop breeders. Homologous recombination, a tightly controlled cell process during the production of gametes in meiosis, is responsible for creation of genetic variation. Owing to the presence of more than two homologous chromosomes, polyploid meiosis faces a variety of challenges, such as multivalent formation and mis-segregation. Using a plant trial with more than 300 diploid and tetraploid Arabidopsis thaliana F2 individuals, significant differences were found in various traits between the two populations. Cytological analysis using FISH on diploid and tetraploid plants revealed an overall increase in meiotic recombination in tetraploids, although the per bivalent frequency was reduced. The process of meiotic recombination was further explored in potato (Solanum tuberosum), a globally important autotetraploid crop. Chiasma frequency and multivalent frequency for chromosomes 1 and 2 varied according to variety, where the diploid variety showed a reduced chiasma frequency compared with tetraploid varieties. Immunolocalisation of the axis and synaptonemal complex proteins, ASY1 and ZYP1, demonstrated the complexities that may arise during meiosis in an autotetraploid plant

    Cycle structure of iterating redei functions

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    Vasiga and Shallit [17] study tails and cycles in orbits of iterations of quadratic polynomials over prime fields. These results were extended to repeated exponentiation by Chou and Shparlinski [3]. We show, using the quadratic reciprocity law, that it is possible to extend these results to Rédei functions over prime fields

    Opioids for breathlessness in heart failure

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    Breathlessness is a common and problematic symptom in heart failure. Opioids have traditionally been considered as analgesics, but a potential role for their use in breathlessness is beginning to emerge. This thesis commences with a review of the existing literature in support of a possible role for opioids in the management of breathless in heart failure. A systematic review of existing human symptom control studies in this thesis suggests that opioid administration may have a small but significant benefit in chronic heart failure. However, only six studies were included in the review and most were either small or of poor methodological quality. This presents a relative gap in the knowledge on this topic. A randomised controlled trial was therefore performed to assess the effect of opioids on breathlessness in chronic heart failure. This crossover trial involved the comparison of two oral opioids with placebo. Thirty-five participants completed the trial, making it the largest trial of its type in this area. Opioid administration was shown to be safe in this patient cohort. No statistically significant differences were demonstrated for breathlessness severity between treatments. Participants were subsequently invited to participate in a three month open label extension. Thirty three participants in total were followed up with thirteen remaining on active therapy. This is the first trial of its type in breathlessness in heart failure and represents the longest participant follow-up in this area. Whilst not as robust as the initial trial, this extension period revealed that opioid continuers rated a statistically significant improvement in breathlessness severity from baseline compared to non-continuers. Finally, a semi-structured interview study in ten participants with heart failure revealed for the first time that opioids are acceptable in this population and they describe troublesome symptoms that might respond to opioid treatment

    On the Degree Growth in Some Polynomial Dynamical Systems and Nonlinear Pseudorandom Number Generators

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    In this paper we study a class of dynamical systems generated by iterations of multivariate polynomials and estimate the degreegrowth of these iterations. We use these estimates to bound exponential sums along the orbits of these dynamical systems and show that they admit much stronger estimates than in the general case and thus can be of use for pseudorandom number generation.Comment: Mathematics of Computation (to appear
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