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Genomic imprinting and evolution of sexually dimorphic traits
Farkačová, Klára ; Kratochvíl, Lukáš (advisor) ; Munclinger, Pavel (referee)
Genomic imprinting is a process whereby expression of an allele differs depending upon its parent of origin. It can be found on autosomes and also on sex chromosomes. Basic hypothesis for the evolution of genomic imprinting is the hypothesis based on the existence of sexual conflict. It can be classified into interlocus sexual conflict and intralocus sexual conflict hypotheses. Under interlocus sexual conflict hypothesis we can diffferentiate parental conflict hypothesis and parent-offspring conflict hypothesis. These theories were historically proposed for the first two taxonomical groups, where genomic imprinting was discovered, namely for angiosperms and placental mammals. Theory of parental conflict proposes that genomic imprinting evolved because the paternally inherited alleles are more selfish to mothers than are the maternally inherited alleles. Parent-offspring conflict hypothesis proposes that genomic imprinting evolved because maternal genes try to regulate demands of paternally inherited alleles in embryos. More recently, genomic imprinting has been found also in other taxons and in alleles, which do not bring any advantage during embryonic development. The intralocus sexual conflict hypothesis is applicable for every trait under sexually-specific selection. It provides potential...
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Origin, degeneration and detection of sex chromosomes
Jílková, Klára ; Král, Jiří (advisor) ; Kratochvíl, Lukáš (referee)
Sex chromosomes evolved from a pair of autosomes and they are differentiated as a result of supression of recombination. This process leads to a successive degradation of odd sex chromosome (alosome), which is becoming genetically inert finally or even excluded. Fundamental processes taking part in degeneration of alosome are Muller's ratchet, genetic hitchhiking, background selection, accumulation of transposable elements and constitutive heterochromatin. Indeed, these processes take part in either degeneration of both Y or W chromosomes. Remarkably, these alosomes show different rates of degeneration, most probably due to 1) different structure of male and female gonads as well as 2) different course of gametogenesis in both sexes. Furthermore, rate of alosome degeneration is usually lower in plants because they are haploid during the major part of life cycle. Other mechanisms of sex chromosome evolution involve rearrangements between autosomes and gonosomes, nondisjunctions and fissions of original sex chromosomes, transformation of B chromosomes into sex chromosomes or non-random segregation of autosomes with sex chromosomes. Other phenomenon that appears in sex chromosome evolution is transition between XY/XX and ZW/ZZ systems or transition between chromosomal sex determination and epigamy. Actually,...
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Karyotype analysis of selected representatives of two pedipalpid orders, Amblypygi and Uropygi
Sember, Alexandr ; Král, Jiří (advisor) ; Ráb, Petr (referee)
Karyotype analysis of selected species from arachnid orders Amblypygi and Uropygi Whip spiders (Amblypygi) and whip scorpions (Uropygi) represent relict arachnid orders which has been found already at Upper Carboniferous strata. Although cytogenetic data from amblypygids and uropygids might be important to reconstruct karyotype evolution of arachnids, cytogenetics of these orders is almost unknown. Presented study is aimed in analysis of karyotype and meiosis in 16 species of Amblypygi and 4 species of Uropygi. Both groups are characterized by considerable range of diploid chromosome numbers (2n = 24 - 86 in Amblypygi and 36 - 66 in Uropygi). Analysed species does not exhibit morfologically differentiated sex chromosomes. Differentiation of sex chromosomes on molecular level was revealed in amblypygid Paraphrynus mexicanus by comparative genome hybridization. Obtained data indicate XY/XX sex chromosome system in this species. Comparison of karyotype data indicates reduction of chromosome numbers during evolution of both orders. In Amblypygi, this reduction was accompanied by increase of number of biarmed chromosomes. This trend is not apparent in Uropygi. Karyotypes of most analysed amblypygids and uropygids are also characterized by low amount of heterochromatin. Most studied species exhibit two pairs...
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Molecular divergence of sex chromosomes compared to autosomes in related species of tortricids
ŠÍCHOVÁ, Jindra
In systems with female heterogamety (e.g. WZ/ZZ; female/male), the Z chromosome has several characteristics that distinguish it from autosomes, such as different effective population size (Ne) and hemizygosity in the heterogametic sex. These characteristics may lead to an accelerated rate of adaptive changes for the Z-linked genes compared to autosomal coding sequences, often referred to as the Fast-Z effect. This work is the first attempt to test the Fast Z effect in Lepidoptera by using two methodological approaches. These included comparative fluorescence in situ hybridizations and comparisons of substitution rates in coding sequences.
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BAC clones as a tool for the study of codling moth \kur{Cydia pomonella} (Lepidoptera: Tortricidae) W chromosome
DALÍKOVÁ, Martina
In the present study, the W sex-chromosome of the codling moth was studied by means of fluorescence in situ hybridization (FISH) with probes prepared from bacterial artificial chromosome (BAC), which were isolated from the codling moth BAC library. The BAC library was screened for clones derived from both the W and Z sex chromosomes using three sets of molecular markers of codling moth sex chromosomes. A total of 54 BAC clones have been obtained. In this work, only 3 W-derived BAC clones and 1 Z-derived BAC clone were further characterized by BAC-FISH mapping on chromosome preparations of pachytene oocytes; the other BAC clones have been retained for next studies. Whereas the Z-BAC probe provided a discrete hybridization signal on the Z chromosome, and surprisingly on the W chromosome, the W-BAC probes showed multiple hybridization signals distributed on the whole W chromosome, suggesting that they are mainly composed of repetitive sequences, which occur in multiple clusters on the W chromosome. The specific pattern of W-BAC hybridization signals along with the discrete signal of the Z-BAC enabled us to discriminate left/right orientation of both the W and Z chromosomes and examine specificity of W-Z pairing during meiotic prophase I.
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Identification of Z-linked genes for the study of sex chromosome evolution in Lepidoptera
PROVAZNÍK, Jan
Moths and butterflies (Lepidoptera) have a WZ/ZZ (female/male) sex chromosome system or its numerical variants. The non-recombining W chromosome is largely formed by heterochromatin, composed of repetitive DNA and almost free of genes. Its use for evolutionary studies is thus limited due to fast molecular divergence. Whereas the Z chromosome resembles to autosomes; it is rich in genes and thus expected to be more conserved. In this study, the Z-linked genes with available DNA sequence information are summarized in order to give reference to suitable candidates for the study on evolutionary history of sex chromosomes in Lepidoptera. The use of Zlinked genes to test current hypotheses on the origin of the lepidopteran W chromosome is also discussed.
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Sex chromosomes in the house mouse hybrid zone
DUFKOVÁ, Petra
Understanding the genetic basis of reproductive isolation is the ultimate goal of the study of speciation. Here I present the results of a study of gene flow and its barriers at sex chromosome markers across the central European portion of the hybrid zone between two house mouse subspecies, Mus musculus musculus and M. m. domesticus. We identified strong introgression of Y musculus chromosome into the domesticus area accompanied by a perturbation of the census sex ratio. In addition, we detected stochastic effects that can distort results of hybrid zone studies. Finally, we confirmed a strong effect of sex chromosomes on reproductive isolation and hence their important role in the process of speciation.
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Structure and evolution of plant sex chromosomes: The use of BAC library
Kejnovský, Eduard ; Lengerová, Martina ; Hobza, Roman ; Široký, Jiří ; Vyskot, Boris
Sex chromosomes of plant species Silene latifolia are the ideal model for evolutionary biology studies because they represent early stages of X and Y chromosomes history. We used fluorescence in situ hybridization (FISH) with bacterial artificial chromosome (BAC) clones in studies of chromosome structure to demonstrate that a majority of genes are located in subtelomeric regions of all chromosomes. Our results also indicate the absence of accumulation of main classes of repetitive sequences - retroelements and centromeric tandem repeats - in non-recombining parts of the sex chromosomes.
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