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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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Comparative cytogenetics of bed bug Cimex lectularius (Heteroptera: Cimicidae)
Sadílek, David ; Vilímová, Jitka (advisor) ; Ráb, Petr (referee)
Comparative cytogenetics of the bed bug Cimex lectularius (Heteroptera: Cimicidae) The human bed bug Cimex lectularius has started enormous spreading to all developed countries of temperate climate zone during the last ten years. Bed bug was almost eradicated by a mass use of DDT in these areas until the 70's in the 20th century. This temporal haematophagous ectoparasite occupies particularly human dwellings and bat roosts. Cimex lectularius shows unusual combination of cytogenetic characteristics, general for all Heteroptera, however, not usual for other organisms. The chromosomes are holokinetic, with completely achiasmatic meiosis and inverted meiosis of the sex chromosomes. Especialy remarkable feature is intraspecific variation of the number of the X chromosomes. The variable number of chromosomes of 43 populations of Cimex lectularius from the Czech Republic and 27 populations from other European countries was studied in the present study. The 10 variants of karyotype were found out by using the "hotplate spreading" method and the standard Giemsa staining. There were male karyotypes with 2n = 29, 30, 31, 32, 33, 34, 35, 37, 42 and 47 chromosomes and two females with peculiar odd number of sex chromosomes X, 2n = 33 and 43, not complementary with any male. A stable number of 2n = 26 autosomes...
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Cytogenetic characteristics of the genus Cimex (Heteroptera: Cimicidae)
Sadílek, David ; Vilímová, Jitka (advisor) ; M. Grozeva, Snejana (referee) ; Král, Jiří (referee)
The present thesis deals with the phenomenon of additional sex chromosomes in Cimex lectularius (Hemiptera: Heteroptera: Cimicidae) using genome size analysis combined with the classical cytogenetic approach. Also, five other cimicid species and 12 species from the family Nabidae were analysed identically for comparative purposes. The thesis also pursues a description of methodical approaches of cytogenetics and flow cytometry in the study of C. lectularius. Recently analysed European specimens of C. lectularius from human host exhibited 12 distinct cytotypes, with a variable number of chromosomes X from two to 20 (2n♂ = 26+X1X2Y to 26+X1-20+Y). The fragmentation hypothesis of C. lectularius additional chromosomes X origin was established in the second half of the 20th century. However, the present genome size measurements suggest that various chromosomal rearrangements as duplication or deletion besides the fragmentation could occur. Males with basic cytotype 2n = 26+X1X2Y had average genome size of 2C = 1.94 pg, in contrast male with 2n = 26+X1-7+Y yielded 2C = 2.26 pg and also specimens with genome size decrease 2C = 1.69 pg appeared. The most informative turned up to be the relative genome size of sperm cells n = 13+X1X2 and n = 13+Y, where specimens with higher chromosome number showed...
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Cytogenetic characteristics of the genus Cimex (Heteroptera: Cimicidae)
Sadílek, David
The present thesis deals with the phenomenon of additional sex chromosomes in Cimex lectularius (Hemiptera: Heteroptera: Cimicidae) using genome size analysis combined with the classical cytogenetic approach. Also, five other cimicid species and 12 species from the family Nabidae were analysed identically for comparative purposes. The thesis also pursues a description of methodical approaches of cytogenetics and flow cytometry in the study of C. lectularius. Recently analysed European specimens of C. lectularius from human host exhibited 12 distinct cytotypes, with a variable number of chromosomes X from two to 20 (2n♂ = 26+X1X2Y to 26+X1-20+Y). The fragmentation hypothesis of C. lectularius additional chromosomes X origin was established in the second half of the 20th century. However, the present genome size measurements suggest that various chromosomal rearrangements as duplication or deletion besides the fragmentation could occur. Males with basic cytotype 2n = 26+X1X2Y had average genome size of 2C = 1.94 pg, in contrast male with 2n = 26+X1-7+Y yielded 2C = 2.26 pg and also specimens with genome size decrease 2C = 1.69 pg appeared. The most informative turned up to be the relative genome size of sperm cells n = 13+X1X2 and n = 13+Y, where specimens with higher chromosome number showed...
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Analýza karyotypu vakonošů (Psychidae, Lepidoptera) metodami klasické a molekulární cytogenetiky
HEJNÍČKOVÁ, Martina
Due to their phylogenetic position, Psychidae play an important role in the investigation of the W chromosome origin in Lepidoptera. Several species of Psychidae were tested for the presence of sex-chromatin and investigated via comparative genomic hybridization. Furthermore, odd chromosome numbers and a Z univalent were observed in females. Overall, this study brings tangible evidence for the absence of the W chromosome in Psychidae, thus contributes to complex knowledge of the W chromosome evolution. In addition, karyotypes of the given species were analyzed using 18S rDNA and histone H3 probes. The results indicate relative stability of their karyotypes.
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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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Evolution of karyotype and sex determination in iguanas (Squamata: Pleurodonta)
Altmanová, Marie ; Kratochvíl, Lukáš (advisor) ; Zrzavá, Magda (referee)
Squamate reptiles in general possess an unusual variability in karyotype and sex determining mechanisms. However, in these two aspects, iguanas (Pleurodonts) are considered as a relatively conservative group of lizards. So far only genotypic sex determination with male heterogamety has been detected in this lineage. However, the sex chromosomes have not been revealed in many species by classical cytogenetics, probably due to their homomorphy. Significant variability in karyotype was observed only in the species-rich genera Anolis, Sceloporus and Liolaemus. The aim of this thesis was to investigate the genome of available species from the main iguanid lineages using classical and molecular cytogenetic methods. As well as finding the karyotype characteristics, which may represent synapomorphies of main iguanid lineages, the other aim was to try to identify sex chromosomes. This study confirmed previously published karyotypes of 13 species and established new descriptions of karyotype for eight species. The chromosomes of all studied specimens were examined by methods of classical and molecular cytogenetics, 21 species covering eight iguanid families were analysed in this thesis. The majority of studied species shared the apparently ancestral karyotype of the group, with diploid chromosome number...
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Proximate control of sexual dimorphism in livebearer Poecilia wingei
Farkačová, Klára ; Kratochvíl, Lukáš (advisor) ; Slavík, Ondřej (referee)
The effect of 17α-methyltestosterone a 17β-estradiol on sex of livebearer fish Poecilia reticulata and P. wingei was studied. Solution of 2.5 mg testosterone was added in the aquarium the first and fifteenth day after delivery of new fry. Estrogen was administered in food to gravid females (400 mg per 1 kg food). Sex of all individuals was determined in one, two and three months. Administration of neither testosterone nor estrogen caused sex reversal; in the second case reproduction of almost all females was stopped.
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Evolution of sex-determining mechanisms and genomes in squamate reptiles (Reptilia: Squamata)
Pokorná, Martina ; Kratochvíl, Lukáš (advisor) ; Marec, František (referee) ; Vyskot, Boris (referee)
Evolution of sex determining mechanisms in squamate reptiles (Reptilia: Squamata) Martina Pokorná Ph.D. thesis Abstract This Ph.D. thesis is focused on the evolution of sex determining mechanisms and genomes in squamate reptiles. It is based on three published articles and two manuscripts. The evolution of sex determining mechanisms, sex chromosomes and genomes, and their organisation, was studied on a wide phylogenetic scale of the whole group of squamate reptiles and some lineages of other Sauropsids, as well as on the small phylogenetic range as a detailed comparative study inside individual lineages of squamates. This thesis is based upon the use of classical cytogenetic methods, methods of molecular cytogenetic (especially fluorescent in situ hybridisation) and the results were analysed using phylogenetic approaches. The results and outputs of this study represent an important contribution to the general knowledge of the principals of sex determination and the evolution of these phenomena not only in squamate reptiles but also in the whole group of amniotes. Using the results obtained during the work on this thesis we can conclude that sex chromosomes evolved in particular lineages of amniotes independently. This origin was in some cases followed by accumulation of microsatellite sequences on sex...
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