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Vývoj molekulárních markerů pro chromozom W u modráska \kur{Polyommatus icarus}
HRUBÁ, Monika
This thesis focuses on development of molecular markers for the W chromosome in the blue butterfly Polyommatus icarus. In this blue butterfly, karyotype races with different constitution of the neo-sex chromosomes were reported. The markers were used for PCR sexing of the early developmental stages to obtain sex-specific total RNA samples for testing a role of sexually antagonistic selection in fixation of neo-sex chromosomes.
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Reconstruction of the evolution of multiple sex chromosomes in \kur{Leptidea} wood white butterflies
HOVORKOVÁ, Kristýna
Having a crucial role in many evolutionary processes, such as sex determination, speciation and adaptation, sex chromosomes tend to be highly conserved. Rapidly evolving sex chromosome systems offer a special opportunity to study the evolution of the sex chromosomes in miraculous resolution. Butterflies of genus Leptidea possess a unique species-specific sex chromosome system with 3-4 W and 3-4 Z chromosomes. Using novel genomic tools established for L. juvernica, namely transcriptome-based microarray for comparative genomic hybridization (array-CGH) and a library of bacterial artificial chromosome (BAC) clones, we assembled the physical maps of Z chromosomes in three cryptic Leptidea species (L. juvernica, L. sinapis, and L. reali) by fluorescence in situ hybridization (FISH) of BAC clones containing orthologs of Bombyx mori genes. In all three species, we identified the 'ancestral' Z chromosome and synteny segments of autosomal origin and reconstructed the step-by-step evolution of multiple sex chromosomes. We propose that the multiple sex chromosome system originated in the common ancestor of Leptidea species by means of multiple chromosomal rearrangements, especially translocations, fusions and fissions, between the sex chromosomes and autosomes. Thus, the turnover of neo-sex chromosomes could not be the main engine driving speciation in this genus. Instead, we propose that subsequent differentiation of the sex chromosome multiples in each species together with enlarged number of Z-linked genes could play a crucial role in accumulation of genetic incompatibilities facilitating subsequent divergence and speciation in Leptidea wood white butterflies.
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Neo-sex chromosomes and their evolutionary significance
Košátko, Prokop ; Král, Jiří (advisor) ; Johnson Pokorná, Martina (referee)
Neo-sex chromosomes arise due to rearrangements between ancestral gonosomes and autosomes. Neo-sex chromosomes are valuable systems for the study of sex chromosome evolution. It is possible to use them for analysis of processes driving the formation of differentiated sex chromosomes, especially suppression of recombinations and alosome degeneration. The most important rearrangements forming neo-sex chromosomes are Robertsonian and reciprocal translocations. Speciation events are important consequences of birth of neo-sex chromosomes. The presented study is focused on the evolution of neo-sex chromosomes in drosophilids, muntjacs, and monotremes. Neo-sex chromosomes emerged in many Drosophila species. The genome of D. albomicans carries the youngest known neo-sex chromosome system, which arised only one hundred thousand years ago. Information from research into Drosophila neo-sex chromosomes underlines the importance of Muller's ratchet and background selection at the beginning of sex chromosome differentiation and hitchhiking and deleterious mutations at the end of this process. Genomes of muntjacs carry young and fast evolving neo-sex chromosomes. In several muntjac species, neo-sex chromosomes form a considerable part of the genome. The neo-sex chromosome systems of monotremes consist of many...
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Evolution of karyotype and sex determination in iguanas (Squamata: Pleurodonta)
Altmanová, Marie ; Kratochvíl, Lukáš (advisor) ; Zrzavá, Magda (referee)
Squamate reptiles in general possess an unusual variability in karyotype and sex determining mechanisms. However, in these two aspects, iguanas (Pleurodonts) are considered as a relatively conservative group of lizards. So far only genotypic sex determination with male heterogamety has been detected in this lineage. However, the sex chromosomes have not been revealed in many species by classical cytogenetics, probably due to their homomorphy. Significant variability in karyotype was observed only in the species-rich genera Anolis, Sceloporus and Liolaemus. The aim of this thesis was to investigate the genome of available species from the main iguanid lineages using classical and molecular cytogenetic methods. As well as finding the karyotype characteristics, which may represent synapomorphies of main iguanid lineages, the other aim was to try to identify sex chromosomes. This study confirmed previously published karyotypes of 13 species and established new descriptions of karyotype for eight species. The chromosomes of all studied specimens were examined by methods of classical and molecular cytogenetics, 21 species covering eight iguanid families were analysed in this thesis. The majority of studied species shared the apparently ancestral karyotype of the group, with diploid chromosome number...
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