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Karyotype evolution of cobweb spiders (Araneae: Theridiidae)
Večeřová, Hana ; Forman, Martin (advisor) ; Dolejš, Petr (referee)
Spiders (Araneae) are diversified order of the subphylum Chelicerata. Majority of the order belongs to group Entelegynae, as well as representatives of cobweb spider family (Theridiidae). Their noteworthy genus is Latrodectus, also known as "black widows". This thesis summarizes basic information about the genus, it's biology, phylogenetics and cytogenetics, with an overlap to genomics of cobweb spiders and their related species. Even though spiders' cytogenetics is an interesting field, particularly due to the occurance of unusual systems of sex chromosomes, some of the questions remain unanswered. A leading trend in entelegyne spiders is the reduction of diploid counts, where most mechanisms of the process remains unclear. Main aim of the thesis was to verify a potential of cobweb spiders as a model system for future studies of these changes. The genus Latrodectus may have potential because of showing suprisingly diverse karyotypes, which is unusual in Entelegynae. Despite their popularity, quality of karyotype data is poor and deserves to be revised. Nevertheless, the cosmopolitan L. geometricus is purposed as a keypart of promising model system for comparison of genome with modern cytogenomic approaches. Establishment of such model system could adress the questions about mechanism of karyotype...
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Evolution of karyotype, sex chromosomes and gene clusters in selected taxa of araneomorph spiders
Voráčková, Diana ; Forman, Martin (advisor) ; Sadílek, David (referee)
Spiders (Araneae) are a diverse group with various sex chromosome systems. The most common is X1X20 sex determination, X1X2 denotes two non-homologous X chromosomes and 0 the absence of Y. The presence of Y chromosome is rare among spiders and has been described mainly in Synspermiata, X1X2Y is probably ancestral constitution for this clade. The family Sicariidae was chosen to elucidate the evolution of sex chromosomes in Synspermiata. Karyotypes of 10 species whose 2n ranged from 19 to 23 were investigated in this study. The most common finding was X1X2Y in all studied Loxosceles species. The derived XY system was discovered in Sicarius. Furthermore, the distributional pattern of molecular cytogenetic markers (genes for 18S rRNA, 5S rRNA, histone H3 and U2 snRNA) was analysed using fluorescence in situ hybridization (FISH). These markers were found exclusively on autosomes, on one or two pairs. FISH with whole-genome probes of both sexes was performed to reveal distribution of Y specific sequences. Various patterns of Y differentiation were found in certain species. Y chromosome was small in all Sicariidae. A larger Y with a pronounced accumulation of Y-specific sequences has been detected in previous works - in the X1X2Y system of a synspermiate Pholcus phalongoides (Pholcidae). Pilot...
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Centric fusions in karyotype evolution of spiders
Mlnáříková, Barbora ; Forman, Martin (advisor) ; Nguyen, Petr (referee)
Entelegynae are the most specious group of spiders. Their karyotypes are characterized by the predominance of X1X20 sex chromosome system and exclusively acrocentric morphology of chromosomes. Mono-armed chromosomes can be the substrate for centric fusion, the rearrangement, in which two acrocentric chromosomes fuse at their centromeric regions and form single bi-armed chromosome. In Entelegynae, centric fusion events followed the "all or nothing" rule, where all acrocentric chromosomes fuse during one event or in a very rapid sequence and karyotype is fully saturated by bi-armed chromosomes. Although the cytogenetics of Entelegynae is relatively well studied, so far, "all or nothing" phenomenon has been observed only rarely, namely in 12 species from 5 families. In this thesis, new data about the occurrence of centric fusion in 12 species from 5 unrelated families are reported. In all cases the "all or nothing" rule was confirmed. Strong female meiotic drive is proposed as the main force responsible for changes in chromosomal morphology of Entelegynae. The persisting of bi-armed chromosomes is likely to be rare in Entelegynae. However, in the family Dictynidae, bi-armed chromosomes are fixed. For a better understanding of karyotype dynamics in this unique family, molecular cytogenetic approaches...
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Evolution of karyotype and sex chromosomes in African and American clades of theraphosid mygalomorph spiders
Turečková, Eva ; Forman, Martin (advisor) ; Šťáhlavský, František (referee)
The family Theraphosidae (tarantulas) are generally known of spiders, often keept as hobby pets. Despite their popularity, many aspect of tarantula biology are still omitted. This include also cytogenetic research. In order, to fill this gap I analysed chromosomal constitution in 13 species of tarantulas belonging to the different genera from Africa and south/central America. Data set in this thesis included, also, the tarantula with so far the best covered genome Acanthoscuria genicullata, and the iconic, giant spider Theraphosa stirmi. Conventional giemsa staining of male meiotic plates was accompanied with visualisation of major rRNA clusters using fluorescence in situ hybridization with 18S rDNA probe. Diploid counts ranges considerably from 31 (Ceratogyrus meridionalis) to 83 (Theraphosa stirmi). In some specimens presence of multivalents indicated a possibility of hybridization of different chromosomal races in a hobby lineages. Various types of differentiated sex chromosomes have been proven, including X0, X1X20 X1X2X30 systems. Interestingly, the diversity in karyotype features was not linked with diversity in major rDNA cluster number. Most of the species displayed one prominent locus located on autosomes. Two species exhibited polymorphism in the presence of one more additive smaller...
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Genes of early meiotic prophase I of spermatogenesis in house mouse
Škaloudová, Eliška ; Trachtulec, Zdeněk (advisor) ; Forman, Martin (referee)
Meiosis is an essential cellular process that is necessary for gamete formation in all sexually reproducing organisms. This work is focused on the description of the genes of early stages of meiotic division in males of a mammalian model, the house mouse. The first part summarizes meiosis focusing on prophase I, which is longer than prophase II. Prophase I is divided into five stages, namely leptotene, zygotene, pachytene, diplotene, and diakinesis. Mouse spermatogenesis and its differences from oogenesis are also briefly described. The second part provides a list of genes encoding proteins required for initiation of meiotic division, pairing and synapses of chromosomes, and initiation of the catalysis of double-strand breaks. Double-strand breaks are repaired by homologous recombination, which may result in so-called crossing-over, the major source of genetic variability. The work deals with the early stage of homologous recombination and components required for this process. Localization of meiotic double-strand breaks in the genome is not random and is under the control of the Prdm9 gene, which seems to take multiple roles, such as the formation of new subspecies of the house mouse. Knowledge of the genes controlling the early stages of meiotic division is a prerequisite to understanding some of...
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Karyotype evolution of velvet spiders (Araneae: Eresidae)
Forman, Martin ; Král, Jiří (advisor) ; Rothová, Olga (referee)
Presented study is aimed to determine basic trends of karyotype evolution in velvet spiders (Eresidae; Araneae). Eresids are burrowing spiders; they includes also some social species. Karyotypes of 16 species of the family Eresidae as well as 2 species of the other families of the superfamily Eresoidea, Hersiliidae and Oecobiidae, are presented. Furthermore, DNA content and base proportion was determined in 14 species. In two species, DNA content of sex chromosomes was also measured. Obtained results revealed considerable variability of diploid numbers, and sex chromosomes systems in eresids. Obtained karyotype data allow to divide eresids into four groups. Karyotypes of the genera Gandanameno, Dresserus and S. lineatus are close to proposed ancestral karyotype of entelegynae spiders and they show the ancestral state of karyotype in velvet spiders. Karyotypes of S. lineatus and E. annulipes differ substantially from other representatives of the genera Stegodyphus and Eresus which indicates paraphyly of these genera. Karyotypes of basal forms are formed by acrocentric chromosomes. Further evolution of eresid karyotypes included considerable reduction of diploid numbers as well as changes of chromosome morphology. Social species of the genus Stegodyphus show tendency to reduce diploid numbers by...
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Karyotype evolution of the Dictyoptera group
Jankásek, Marek ; Šťáhlavský, František (advisor) ; Forman, Martin (referee)
Diploidní počty chromosomů a komentář k jejich morfologii pro 107 druhů řádu Mantodea ♂ - , 126 druhů skupiny "Blattaria" ♂ - a 84 druhů skupiny Isoptera ♂ - této bakalářské práci s meiotickému dělení a chromosomovým mechanismem určení pohlaví. Pozornost byla také dána některým zvláštním prvkům karyotypu skupiny Dictyoptera jako je premetafázní protažení a formace rozličných chromosomálních multivalentů. Celková informace o karyotypech skupiny Dictyoptera je vztažena k řádu Mantodea, principy karyotypových změn napříč evolucí některých nově definovaných skupin mohly být navrženy. Ve skupině "Blattaria" není možné utvářet jakékoliv širší úsudky o karyotypové evoluci, jelikož většina cytogeneticky studovaných druhů je z čeledí "Ectobiidae" a Blaberidae, pro které stále chybí detailnější fylogenetická studie. Některé evoluční trendy mohly být vyneseny ve skupině Isoptera, jakožto formace rozličných chromosomových sexuálních multivalentů a častá fúze jednoramenných chromosomů. Klíčová slova:
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Recombination hot-spots in various organisms
Stočesová, Lucie ; Holá, Dana (advisor) ; Forman, Martin (referee)
Meiotic recombination is an important process which occurs in sexually reproducing organisms and creates new allelic combinations. Frequency and distribution of crossing-overs (COs) are affected by many internal and external factors. Regions with higher frequency of COs are called recombination hot-spots and in this thesis, they are divided into ancestral and derived hot-spots. Ancestral hot-spots are the more original ones and they are determined by histone modifications, nucleosome-depleted regions, promoters and sequence motifs. This type of hot-spots occurs, e.g., in yeasts, birds and plants. Derived hot-spots are determined by the PRDM9 protein, which searches for specific sequence motifs and creates histone modifications. These hot-spots are typical for most mammals except the canines which lost functional PRDM9 due to the mutation of the Prdm9 gene. Activity of PRDM9 destroys primary locations of hot- spots via gene conversion. This process is called "hot-spot paradox" and is solved by the rapid evolution of alleles of the Prdm9 gene. This thesis summarizes basic information on distribution and determination of hot-spots among various eukaryotes. It particularly focuses on the PRDM9 protein, its structure, function and evolution. A determination of location of recombination in species...
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Robertsonian translocations and their involvement into genome evolution
Mlnáříková, Barbora ; Forman, Martin (advisor) ; Sember, Alexandr (referee)
Chromosome aberrations play an important role in human pathologenesis as well as in evolution of many organisms. Robertsonian translocation or centric fusion are the most frequent chromosomal rearrangements in mammals. The most investigated model for their research is house mouse Mus musculus. The standard karyotype of a mouse consists from 40 acrocentric chromosomes, notably there are more than one hundred wild populations that are characterized by various combination of metacentrics, formed by centric fusion of different acrocentrics. Several models have been proposed for the formation of metacentrics, taking account of the sequential structure of their centromeres and short arms in mouse. Segregation distortion in favor of metacentrics is present in female and/or male meiosis, such as meiotic drive can positively affect the degree of fixation of metacentric chromosomes in certain population. Centric fusions have been also presented in evolution of other organisms. Cytogenetic data in spiders indicate the possibility of similar phenomena in the most diversified group of spiders, Entelegynae. Spiders are notable for their unusual sex chromosome systems. Centric fusions also play an important role in the evolution of sex chromosomes and the formation of neo-sex chromosome systems. So far, there is...
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