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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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Molecular composition and ultrastructure of holokinetic chromosomes
Šejgunovová, Nikola ; Král, Jiří (advisor) ; Dalíková, Martina (referee)
Holokinetic chromosomes are a specific type of chromosomes which differentiate from standard (monocentric) chromosomes especially by a diffuse form of domain which binds microtubules (holocentromere). It is related to changes on an ultrastructural and molecular level. These changes are shown in modifications in mitotic and meiotic division and in evolution of karyotypes. Holokinetic chromosomes don't have a primary constriction with a localized centromere and therefore neither an inner centromere domain which would connect sister chromatids. Kinetochore structure of holokinetic chromosomes seems to be simpler than kinetochore structure of monocentric chromosomes. Kinetochore covers most of the surface of mitotic chromosomes. There have been described several variants of meiosis of holokinetic chromosomes which differentiate by position of kinetochore on chromosomes. On a molecular level holokinetic chromosomes differentiate from monocentric chromosomes by a distribution of proteins of a centromere-kinetochore complex, which cover most of the surfaces of mitotic and meiotic chromosomes. This applies, for example, to centromeric histone H3 (CENH3), whose amount and distribution changes during interphase and nuclear division, which is unique in comparison to monocentric chromosomes. The distribution...
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Molecular composition of constitutive heterochromatin
Pajpach, Filip ; Král, Jiří (advisor) ; Holá, Dana (referee)
Constitutive heterochromatin of eukaryotes includes various types of repetitive DNA and transposons characteristic for given region. DNA of centromeric and telomeric re- gions is usually highly methylated and transcribed to RNA transcripts, which participate in formation, functions and spreading of heterochromatin along with histones, their mod- ifications and non-histone proteins. The most typical histone modification in heterochro- matin is methylation, which forms the binding site for protein HP1. This protein (and his paralogues in other eukaryotes except for S. cerevisiae) participates in formation of com- plexes including other proteins like histone methylases SUV39H and their paralogues. Es- sential are also telosome proteins regulating telomeric heterochromatin, Polycomb group proteins and many others, for instance MBD1, Epe1, SUMO and DNA methylases DNMT. Many proteins form complexes, which partake in mechanisms necessary for heterochro- matin maintenance, for example RDRC and RITS complexes in RNA interference, SHREC complex in heterochromatin spreading, and PRC complexes forming heterochromatin in specific situations. Key words: centromere, DNA, histone, HP1, constitutive heterochromatin, methylation, modification, protein, RNA, specific, telomere
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Yeast gene silencing.
Tarabová, Eva ; Kuthan, Martin (advisor) ; Schierová, Michaela (referee)
Each cell contains a complete copy of the entire genetic equipment of the organism. However not all genes are expresed, cells are differentiated in higher eukaryots and only certain proteins are transcribed in each cell. This is possible thanks to a gene silencing, that is stable throughout the whole cell cycle and epigeneticaly inherited from one generation to another. Gene silencing serves also in the maintainance of the chromosomal integrity, it is connected with the right progression of the cell division. It even enables mating type switching and ensures right cells' identity in yeasts. The basis is compact and a higher-ordered structure of chromatin called heterochromatin. The mechanism is common to many various organisms, although the proteins, which ensure silencing, are different.
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