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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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Relationship between the coat colour and melanoma occurrence in horses
Hovorková, Kristýna ; Hofmanová, Barbora (advisor) ; Majzlík, Ivan (referee)
The literary review is divided into two main parts, the first part is dealing with the coloring of horses and their genetic base and the second part is dealing with melanoma formations of horses and their division. In the chapter about several color types of horses there is a description of forming basic color types which is done by three locuses: COLOR, EXTENSION and AGOUTI. Locus COLOR (CREAM) controls whether or not to create pigment. EXTENSION locus controls about the type of pigment and AGOUTI locus controls the distribution of pigment.
The next subsection gives a breakdown of the white color in horses. Greying proces is related with locus GREY where there is a loss of pigment and the coat itself. This process and mutation is commonly connected with dermal melanoma. Non-pigmented spots called vtiligos are connected with the greying process, which is more intense with increasing age. Vtiligios are commonly found in grey horses, at the same locations as dermal melanoma. The places are perianal area under the tail, around the vulva, lips, eyes and around the penis.
Melanoma formations are divided according to whether they occur in Grey horses or other colored horses and whether they have a benign or malignant potential. A further breakdown of melanomas at grey horses is whether it is a separate, smaller segments or large, associated lesions, when this condition is called dermal melanomatosis.
At the end of the thesis there is a description of the treatment options for melanoma. The most effective appears to be a surgical removal of smaller formations. There were studies which have examined the anticancer action of the drug cimetidine but the results are not yet sufficiently conclusive. As preventing the occurrence of melanoma in grey horses it is appropriate to implement the necessary measures and individuals who are concerned should not be included in the next breeding.
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