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Studying the evolution of chromosome rearrangements in pipid frogs using in situ hybridization
Bergelová, Barbora ; Knytl, Martin (advisor) ; Johnson Pokorná, Martina (referee)
In African pipid frogs we can find at least eight polyploidization events in which a lot of levels of ploidy arose. This group includes diploid, tetraploid, octoploid, and/or dodecaploid species. Due to this great variability in ploidy levels, representatives of the genus Xenopus are excellent model organisms for studying the evolution of whole-genome duplications and chromosomal rearrangements. Currently, little information is known about chromosomal rearrangements within the Xenopus species, specifically, there are only two known cases of large-scale rearrangements. The first is a fusion of chromosomes 9 and 10 in the subgenus Xenopus and the other rearrangement is a non-reciprocal translocation occurring between chromosomes 2 and 9 in the subgenus Silurana. In this diploma thesis, we attempted to expand the knowledge about chromosomal rearrangements using the fluorescence in situ hybridization method. We confirmed the fusion of chromosomes 9 and 10 in other species of the Xenopus genus, such as X. pygmaeus, and proposed a hypothesis about the possibility that this fusion occurred in the common diploid ancestors of this subgenus. We also gained further insights into the origin of non-reciprocal translocation within the Silurana subgenus. This translocation was not detected in the species X....
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Cytogenetics of bed bugs (Cimicidae) as a model representative of true bugs (Heteroptera)
Sadílek, David ; Vilímová, Jitka (advisor) ; Johnson Pokorná, Martina (referee)
Cytogenetics of bed bugs (Cimicidae) as a model true bugs (Insecta: Heteroptera) The thesis provides current opinions about a phylogeny of bed bugs, family Cimicidae, and their classification within the order Heteroptera. There are briefly summarized cytological data about the order Heteroptera, known karyotypes of the cimicid subfamilies and introduction to cytogenetics of species Cimex lectularius Linnaeus, 1758. Heteroptera species differ from other organisms by holokinetic chromosomes, a character, in which quite frequently take place chromosomal fragmentation and fusion. Several families posses smaller pair of m chromosomes, which behave during meiosis differently from the other chromosomes. Diploid chromosomal number is extremely variable, it ranges from four (family Belostomatidae) to 80 chromosomes (family Miridae). The behavior of chromosomes in the family Cimicidae is very specific. Sex-chromosomes univalents are connected by thread-like collochores and form so-called pseudobivalents during achiasmatic post-reductional meiosis. Rare polymorphism in a number of X chromosomes occurs in Cimex lectularius populations. The diploid karyotype always consists of 26 autosomal chromosomes and at least two but up to 15 X chromosomes and one Y chromosome. The number of X chromosomes can be variable...
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Use of cytogenetical methods in taxonomy of Arachnida (Arachnida)
Alaverdyan, Argam ; Šťáhlavský, František (advisor) ; Johnson Pokorná, Martina (referee)
This bachelor thesis deals with the use of cytogenetic methods in taxonomy of Arachnida. To understand this matter, we need to analyse available information about inter and intraspecific karyotype variability of individual orders. At the beginning of the thesis there is a description of cytogenetic methods used with Arachnida.They are used to gather the karyotype's fundamental information, such as the diploid number of chromosomes, chromosome morfology and possible occurence of sex chromosomes. Main part of the thesis is focused on describing karyotypes of selected orders (Amblypygi, Palpigradi, Pseudoscorpiones, Scorpions, Opiliones and Araneae) and considering the convenience of use of cytogenetic methods for their taxonomy based on these information. The thesis includes current number of described genera (species) of the orders, as well as a number of cytogenetically analyzed genera (species) for comparison.
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Karyotype analysis of selected groups of tetrapulmonate arachnids
Reyes Lerma, Azucena Claudia ; Sember, Alexandr (advisor) ; Johnson Pokorná, Martina (referee) ; de Bello Cioffi, Marcelo (referee)
Arachnids are a highly speciose group of arthropods with about 130 000 extant species from 12 orders. Some arachnid species are of economic and medical interest. They also offer various opportunities to study the link between genome and karyotype variability and morphological and ecological diversification, evolution and adaptation. The knowledge about arachnid karyotypes and genomes is, however, still limited. The available data show wide range of diploid chromosome numbers (2n), monocentric or holocentric chromosomal structure, variability in sex chromosome systems (especially in spiders) and modifications of meiosis. The main objective of this doctoral thesis was to study by conventional and molecular cytogenetic methods the mechanisms of karyotype evolution in haplogyne spiders (with monocentric and holocentric chromosomes), and further in two families (Charinidae and Phrynidae) from the closely related order Amblypygi. The selected groups offer unique insights into fundamental karyotype traits of the arachnid clade Tetrapulmonata, and they also enable to analyse the role of polyploidy in arachnid karyotype evolution and the evolutionary mechanisms behind the emergence of holocentric chromosomes. Our data suggest that holocentric chromosomes are an autoapomorphy for the haplogyne superfamily...
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Analysis of sex chromosomes and gene clusters in selected mygalomorph and araneomorph spiders
Pappová, Michaela ; Král, Jiří (advisor) ; Johnson Pokorná, Martina (referee)
1 Abstract: The diploma thesis focuses on study of sex chromosomes evolution and repetitive organized genes of chosen mygalomorph and araneomorph spiders. Spiders are characterized by complexicity of sex chromosome systems, their karyotypes contain multiple sex chromosomes X. Besides multiple X chromosomes they also contain a pair or two pairs of nondiferentiated sex chromosomes X and Y. The used methods include methods of classical cytogenetics (preparation of chromosome slides, C-banding) and methods of molecular cytogenetics (fluorescent in situ hybridization and comparative genome hybridization). Complex sex systems were discovered in the studied Theraphosidae spiders. In Theraphosidae spiders Atropothele socotrana and Poecilotheria vittata neo-sex chromosomes were found. Analysis of molecular differentiation of sex chromosomes suggests low differentiation of Y chromosome in neo-sex chromosomes and pair of nondifferentiated sex chromosomes XY. In haplogyne spider Kukulcania aff. hibernalis (X1X2Y), the Y chromosome was significantly differentiated, male specific signal covered the whole chromosome. Detection of 18S rDNA showed that karyotypes of majority of analysed Theraphosidae spiders and haplogyne spiders contain low number (1 or 2) of nucleolar organizing regions localized terminally, which...
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Comparison of the rate of evolution in genes located on reptile sex chromosomes and autosomes
Kuldanová, Kateřina ; Johnson Pokorná, Martina (advisor) ; Reifová, Radka (referee)
According to the "faster-X effect", X-linked genes and Z-linked genes evolve more quickly than autosomal genes. This theory is one of the currently intensively studied topics in evolutionary research. However, performing high quality tests is difficult because the results are influenced by several factors - the effective size of the population of the gonosome, sexual selection, the dependency of mutation rate and selection on sex, and the mechanism of dosage compensation. Conservation of genes and possible differences between rates of evolution of autosomes also play a role and not all studies take this fact into account. This study shows some of the difficulties of paired comparisons of dN/dS ratios traditionally used to test faster-X or faster-Z effects and introduces the basis of a new method of comparison of the rate of evolution (CREC) based on relative genetic distances between three species. The CREC method reduces the influence of conservation of genes on results and is more applicable for testing faster-X or faster Z effects in such species where two species without homologic gonosomes can be found for comparison. In means of the development of this method, the faster-Z effect was tested on a dataset of 9 autosomal and 13 Z-linked genes in the six-striped long-tailed lizard (Takydromus...
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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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Use of cytogenetical methods in taxonomy of Arachnida (Arachnida)
Alaverdyan, Argam ; Šťáhlavský, František (advisor) ; Johnson Pokorná, Martina (referee)
This bachelor thesis deals with the use of cytogenetic methods in taxonomy of Arachnida. To understand this matter, we need to analyse available information about inter and intraspecific karyotype variability of individual orders. At the beginning of the thesis there is a description of cytogenetic methods used with Arachnida.They are used to gather the karyotype's fundamental information, such as the diploid number of chromosomes, chromosome morfology and possible occurence of sex chromosomes. Main part of the thesis is focused on describing karyotypes of selected orders (Amblypygi, Palpigradi, Pseudoscorpiones, Scorpions, Opiliones and Araneae) and considering the convenience of use of cytogenetic methods for their taxonomy based on these information. The thesis includes current number of described genera (species) of the orders, as well as a number of cytogenetically analyzed genera (species) for comparison.
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Cytogenetics of bed bugs (Cimicidae) as a model representative of true bugs (Heteroptera)
Sadílek, David ; Johnson Pokorná, Martina (referee) ; Vilímová, Jitka (advisor)
Cytogenetics of bed bugs (Cimicidae) as a model true bugs (Insecta: Heteroptera) The thesis provides current opinions about a phylogeny of bed bugs, family Cimicidae, and their classification within the order Heteroptera. There are briefly summarized cytological data about the order Heteroptera, known karyotypes of the cimicid subfamilies and introduction to cytogenetics of species Cimex lectularius Linnaeus, 1758. Heteroptera species differ from other organisms by holokinetic chromosomes, a character, in which quite frequently take place chromosomal fragmentation and fusion. Several families posses smaller pair of m chromosomes, which behave during meiosis differently from the other chromosomes. Diploid chromosomal number is extremely variable, it ranges from four (family Belostomatidae) to 80 chromosomes (family Miridae). The behavior of chromosomes in the family Cimicidae is very specific. Sex-chromosomes univalents are connected by thread-like collochores and form so-called pseudobivalents during achiasmatic post-reductional meiosis. Rare polymorphism in a number of X chromosomes occurs in Cimex lectularius populations. The diploid karyotype always consists of 26 autosomal chromosomes and at least two but up to 15 X chromosomes and one Y chromosome. The number of X chromosomes can be variable...
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