National Repository of Grey Literature 23 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
Speciation genomics in nightingales
Mořkovský, Libor ; Reifová, Radka (advisor) ; Macholán, Miloš (referee) ; Piálek, Lubomír (referee)
Speciationisusuallyaslowprocessoccurringoverthousandstomillionsofyears.Thismakes speciation research difficult because no direct observation or manipulation is possible. At best, we can gain some insight by inferring the population history and structure in very fine detail by investigating genetic markers in multiple individuals of the nascent species. Today, speciationresearchisinanunprecedentedpositionthankstotheadventofhigh-throughput sequencingmethods,whichmakeiteasier and cheaper than ever before to evaluate multiple markers in many individuals. Speciation is not a straightforward process that happens in the same way every time, but rather a phenomenon occurring when genetic and ecological circumstancesactinginsymphonyultimatelyleadtoreproductiveisolationoftwosubpopula- tions. This is why it is important to study multiple model systems to understand the general principles behind speciation. We worked with two species of nightingales (Luscinia luscinia andL.megarhynchos)thatdivergedapproximately1.8Mya,likelyduetoglacialfluctuations in Europe. Our main goal was to use these new high-throughput sequencing methods to (1) detect interspecific hybrids between the species, (2) estimate levels of interspecific gene flow,(3)findareasofthenightingalegenomethatunderliereproductiveisolationand,finally, (4)...
Meiosis and fertility of juvenile mouse males
Valtrová, Pavlína ; Trachtulec, Zdeněk (advisor) ; Reifová, Radka (referee)
This work is a summary of literature on pecularities of spermatogenesis in juvenile mouse males (Mus musculus) and their utilization. Spermatogenesis is a process that leads through meiosis to sperm production. The cell undergoes in waves the following cell types: spermatogonia, spermatocytes, spermatids, and spermatozoa. Juvenile mice (whose testes size and sperm count have not reached their maximum) are often used to study individual cell types. The transition between cell types takes shorter time in juveniles. Spermatozoa from the 1st wave of spermatogenesis (WS) are derived from prenatal gonocytes, allowing earlier sperm production. They have a lower frequency of crossing over (CO rate) due to a different processing of CO intermediates; the consequence can be aneuploidy (one chromosome less/more). Spermatozoa from the 2nd WS still display lower CO rate. In 3rd WS testes descend and their temperature decreases to 33řC; CO rate is more like in adults. In 4th WS is typical testicular supportive cells mature and CO rate is similar to adult levels. Juvenile males also suffer from more frequent and severe sperm malformations. Low CO rate should not have an impact on fertility; errors are eliminated during meiotic checkpoints. However, the children of young fathers have a higher risk of aneuploidy,...
Genomic approaches for studying speciation
Vozárová, Zuzana ; Reifová, Radka (advisor) ; Hulva, Pavel (referee)
Technological advances in DNA sequencing along with the emergence of new informatics approaches have created new possibilities in many biological fields. In this bachelor thesis, I will focus on the informatics approaches used in speciation genomics, that is research field focused on the problematics of the origin of new species. I will introduce some statistical methods used by these approaches for parameter estimation. The four particular methods I will write about are Maximum likelihood estimation, Bayesian model, Markov chain Monte Carlo and Iterative approach. I will describe several methods used for the detection of interspecific hybrids and recent as well as historical interspecific gene flow. These methods include NewHybrids, the hybrid index, genomic and spatial clines and coalescent-based methods. The thesis demonstrates the usefulness of the connection of applied mathematics and genomics for addressing general biological issues, and speciation particularly.
Current approaches to whole genome sequencing and de novo genome assembly
Halenková, Zuzana ; Reifová, Radka (advisor) ; Röslein, Jan (referee)
The cost of sequencing has fallen almost ten thousand times over the past ten years due to the development of second and third generation sequencers. Sequencing and assembling the whole genome sequence of an organism is thus becoming a more affordable tool which can be utilized in many fields of science. On the way to the complete DNA sequence of an organism, multiple important decisions have to be made. These are crucial for the successful assembly of high- quality whole genome sequence and regard sample preparation, choice of sequencing technique and choice of an appropriate approach to whole genome assembly. This bachelor thesis describes various methods which can be utilized in individual steps of the process and aspects to consider while making the decisions. Keywords: next generation sequencing, third generation sequencing, whole genome sequencing, de novo assembly, genome assembly algorithms
Sperm morphology in the secondary contact zone of Common Nightingale and Thrush Nightingale
Opletalová, Kamila ; Reifová, Radka (advisor) ; Piálek, Jaroslav (referee)
The male gametes (sperms) are under strong sexual selection and are therefore very diverse in their morphology and often differ even amongst closely related species. Sperms are thus assumed to play very important role in reproductive isolation between species, due to their fast evolution in morphology. In my master thesis, I have studied the possible role of sperm morphology divergence in reproductive isolation in two sister species of passerine birds, the common nightingale (Luscinia megarhynchos) and the thrush nightingale (L. luscinia). The areas of these species overlap in secondary contact zone running across central and Eastern Europe, where they occasionally hybridize. I have compared sperm morphology of males of both species originating in allopatric and sympatric localities as well as interspecies hybrids. The results showed significant differences in total sperm length which is approximately 20 % longer in the common nightingale. That is caused by great interspecies divergence in midpiece (containing mitochondria) length. Interspecific hybrids showed sperms with intermediate length but despite expectations completely morphologically normal. This outcome corresponds with observed fertility in F1 hybrid males. What I consider to be an essential finding is a significant divergence in head...
Comparison of the rate of evolution in genes located on reptile sex chromosomes and autosomes
Kuldanová, Kateřina ; Johnson Pokorná, Martina (advisor) ; Reifová, Radka (referee)
According to the "faster-X effect", X-linked genes and Z-linked genes evolve more quickly than autosomal genes. This theory is one of the currently intensively studied topics in evolutionary research. However, performing high quality tests is difficult because the results are influenced by several factors - the effective size of the population of the gonosome, sexual selection, the dependency of mutation rate and selection on sex, and the mechanism of dosage compensation. Conservation of genes and possible differences between rates of evolution of autosomes also play a role and not all studies take this fact into account. This study shows some of the difficulties of paired comparisons of dN/dS ratios traditionally used to test faster-X or faster-Z effects and introduces the basis of a new method of comparison of the rate of evolution (CREC) based on relative genetic distances between three species. The CREC method reduces the influence of conservation of genes on results and is more applicable for testing faster-X or faster Z effects in such species where two species without homologic gonosomes can be found for comparison. In means of the development of this method, the faster-Z effect was tested on a dataset of 9 autosomal and 13 Z-linked genes in the six-striped long-tailed lizard (Takydromus...
The role of hybridization in animal evolution
Šárová, Markéta ; Reifová, Radka (advisor) ; Černá Bolfíková, Barbora (referee)
There is a growing number of studies showing that interspecific hybridization and gene introgression have a creative role in the evolution of animals. These studies emphasize that hybridization and a gene introgression represent an important source of a genetic variability. Within the process of adaptive introgression, adaptive traits may spread among species and help them to colonize new environments. Interspecific hybridization may also contribute to the emergence of new phenotypes and evolutionary novelties and thus contribute to adaptive radiations. Hybridization can be also a cause of parallel evolutions in many organisms. Another way how hybridization affects evolution is related to a speciation. Hybrid speciation could be one of ways how new species arise, and in this way increase the biodiversity. However in many cases the hybridization has an opposite impact on species richness and present a danger of species extinction by hybridization. The aim of this bachelor thesis is to explain and discuss the above described processes, introduces selected examples of animals related to these processes, and finally evaluate the role of interspecies hybridization in animal evolution. Key words: interspecific hybridization, adaptive introgression, adaptive radiation, parallel evolution, hybrid speciation
Evolutionary importance of mixed singing in two species of nightingales
Kohoutová, Hana ; Reifová, Radka (advisor) ; Sedláček, Ondřej (referee)
Singing is important for communication in birds. Some species of birds copy singing from other species. This heterospecific copying of singing is common especially in closely related bird species, and is usually called mixed singing in such cases. Mixed singing is often asymmetric, when only one species of the pair copies a song of the congener. The meaning of mixed singing is not well explained yet. The most common mechanism is probably an error during the learning phase of singing, but in some cases mixed singing can be adaptive. In my master's thesis I deal with the evolutionary meaning of mixed singing in two closely related passerine species - Common nightingale (Luscinia megarhynchos) and Thrush nightingale (Luscinia luscinia). These species co-occur in secondary contact zone in central and eastern part of Europe. Only Thrush nightingale which is larger and probably a more dominant species, exhibits mixed singing. In playback experiments in Common nightingale I studied a possible adaptive meaning of mixed singing in relation to interspecific communication. I tested the differences in behavioural and vocal response of Common nightingales to three types of stimuli: pure singing of Common nightingale, pure singing of Thrush nightingale and mixed singing of Thrush nightingale. The tested males...
Haldne's rule and mechanisms of hybrid female sterility in birds
Baránková, Lucie ; Reifová, Radka (advisor) ; Jansa, Petr (referee)
Hybrid sterility is one of the mechanisms of intrinsic postzygotic reproduction barriers between species and plays a key role in the process of speciation, which is emergence of new species. In accordance with Haldane's rule, hybrid sterility affects preferably the heterogametic sex, which means that in organisms with XY chromosomes, such as mammals or drosophila, male sterility will be affected by sterility of hybrid offspring, while organisms with ZW chromosomes such as birds or butterflies, will be a sterile hybrid female. Symptoms and mechanisms of hybrid sterility are well studied in organisms with heterogametic males, whereas far fewer studies have been performed on organisms with heterogamous females. In my bachelor thesis I will introduce the basic theories explaining the two general rules of speculation, the Haldane rule and the associated great influence of chromosome X or Z on the occurrence of hybrid sterility. Furthermore, in my work I will deal with the manifestations of hybrid sterility of females in birds and in the selected species will introduce the mechanisms that cause this sterility. Key words: Haldane's rule, hybrid sterility, speciation, birds, postzygotic izolation
Mutation and substitution rates in sexual and asexual forms: a clue to the persistence of sex in a model group of Cobitis?
Röslein, Jan ; Janko, Karel (advisor) ; Rothová, Olga (referee) ; Reifová, Radka (referee)
TITLE: Mutation and substitution rates in sexual and asexual forms: a clue to the persistence of sex in a model group of Cobitis? AUTOR: Jan Röslein DEPARTMENT: Ústav živočišné fyziologie a genetiky AVČR, v.v.i. SUPERVISOR: Mgr. Karel Janko, Ph.D. ABSTRACT: Subject of this thesis is to test several hypotheses about the evolution of asexual reproduction in model group of fish family Cobitis and its mutual competition among sexual and asexual forms, which touches one of the oldest unresolved issues of biology. Specifically, the work deals with the accumulation of non-synonymous mutations, which accelerated accumulation in the genome of clonal lineages theoretically leads to increased extinction compared with sexually reproducing populations (so-called. The theory of Muller's ratchet and Kondrashov's hatchet). This thesis is based on a normalized cDNA sequencing data from oocytes and liver tissue, which has served as a base matrix (generated based on non-normalized cDNA data) for transcriptome sequencing (RNAseq). Consequently, the RNAseq data have served as validation for acquired polymorphisms, detection of differential expression of allele- specific expression (ASE) hybrid biotypes. This diploma thesis balances among the edges of vast spectrum of hypotheses regarding the evolution of the genus hybrid...

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