National Repository of Grey Literature 4 records found  Search took 0.01 seconds. 
Triploid plants: barriers or mediators of gene flow in mixed-ploidy species?
Voltrová, Alena ; Kolář, Filip (advisor) ; Hojka, Jakub (referee)
The aim of this work is to review our knowledge on the evolutionary significance of triploid plants, modes of their origin and mechanisms preventing triploid formation, and to answer the question of whether triploids act rather as mediators or barriers in gene flow between populations possessing different numbers of chromosome sets (diploid and tetraploid). The production of unreduced gametes is considered to be the major pathway of triploid formation in otherwise diploid populations, following the merger of haploid and diploid gamete. In contrast, in mixed di-tetraploid populations, triploids are usually formed by interploidy hybridization. The frequency of formation and fitness of triploids is reduced by a number of reproductive barriers, both pre- and postzygotic, the most important of which is the so-called triploid block caused by an unbalanced ratio of originally maternal and paternal genes in the nourishing tissue endosperm. Although the formation of triploids is accompanied by many barriers, which also further translate to their reduced viability, followed by additional reduction in fertility due to meiotic problems, triploids play a more important role in populations than might be expected solely on the basis of their rare occurrence in nature. Triploids act as mediators of gene flow...
Secondary metabolites and their utilisation in Urtica dioica agg.
Pekařová, Michaela ; Urfus, Tomáš (advisor) ; Hojka, Jakub (referee)
Stinging nettle (Urtica dioica) is a very well-known taxon of genus Urtica, but still its taxonomy is not satisfactory resolved. An obvious reason of taxonomic obscurity of entire aggregate is enormous morphological variation. Polyploidization significantly contributes to this variability. Polyploidy probably is a reason of successful expansion of tetraploid cytotype in synanthropic habitats. Urtica dioica is rich in secondary metabolites, especially fatty acids, phenolic acids and flavonoids. Secondary metabolites are isolated for various purposes. They are widely applied especially in pharmacy and subsequently used for various medications. Despite the undoubtful economic importance a linkage between secondary metabolites composition and polyploidy has not been studied yet.
Introgressive zone of Arabidopsis lyrata and A. arenosa in Central Europe
Hojka, Jakub ; Marhold, Karol (advisor) ; Španiel, Stanislav (referee)
Genetic composition of hybrid zones often reflects geographical and ecological gradients. Hybrid zone of Arabidopsis lyrata and A. arenosa in Central Europe can be convenient model system for testing such hypothesis. These are well circumscribed but still interfertile, and their offspring is fully fertile. Besides repeated hybridisation events, the current state is complicated by the autopolyploidisation events of one of the parents, namely A. lyrata, which is present in the area studied both as diploid and tetraploid. This hybrid zone was already described in previous publications, which showed certain gradient of introgression. Moreover, the area of the hybrid zone represents a transition between Alpine and Pannonian climate along an altitudinal gradient leading from the Prealps to the lowland Wienerwald. The current thesis is the as yet most detailed study of this hybrid zone both in respect of number of studied populations and the amount of data acquired using the methods of RAD Sequencing, multivariate morphometrics and flow cytometry. The analysis of genetic data showed a gradient of introgression, where parental populations are placed at opposite ends, whereas genetically intermediate hybrids are placed in its centre. Analysis of the genome size showed an additional gradient, where hybrids...
Is there any influence of ecological gradient on the introgression and its evolutionary consequences in the genus Arabidopsis?
Hojka, Jakub ; Marhold, Karol (advisor) ; Mráz, Patrik (referee)
1 Hybridization, introgression and polyploidy, especially in their combination, belong to the most important speciation processes in vascular plants. Athough basic features of these processes are generally well known, their cases in particular groups of plants and concrete cases differ a lot and their studies often bring interesting results. In the genus Arabidopsis several cases of combined hybrid and polyploid speciation are known (e.g. A. kamchatica, A. suecica) and there are also cases where we expect introgressive hybridization (e.g. between A. arenosa and A. petraea). The aim of the bachelor thesis is an evaluation of known cases of homo- and heteroploid introgressive hybridization and hybrid speciation in the genus Arabidopsis in the context of similar cases in the family Brassicaceae and perhaps also other families of vascular plants. Next aim is to design method of detailed evaluation of the introgressive zone of A. arenosa and A. petraea (= A. lyrata subsp. petraea) in Central Europe using mophological, cytometric and molecular evidence as well as ecological parameters of studied localities. Set of morphological characters will be tested on the currently available material of A. arenosa that is cultivated at CEITEC Brno as part of the finalised GACR project.

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