Sex chromosomes in reptiles: co-option or homology?

• Thesis title in Czech: Pohlavní chromosomy plazů: koopce, nebo homologie?
• Thesis title in English: Sex chromosomes in reptiles: co-option or homology?
• English key words: reptiles, sex chromosomes, co-option, cytogenetics, chromosome, molecular, genetics, bioinformatics, next generation sequencing, zoology, ecology, qPCR, PCR, evolution, amniotes
• Academic year of topic announcement: 2016/2017
• Thesis type: dissertation
• Thesis language: angličtina
• Department: Department of Ecology (31-162)
• Supervisor: Michail Rovatsos, Ph.D.

Preliminary scope of work in English

Reptiles possess two major systems of sex determination: Environmental Sex Determination (ESD) and Genotypic Sex Determination (GSD), either with male (XX/XY sex chromosomes) or female (ZZ/ZW) heterogamety. There are two major hypotheses concerning the evolution of sex chromosomes across reptilian lineages and in fact whole amniotes: the "evolutionary trap" and the "super sex-chromosome". According to the "evolutionary trap" hypothesis, ESD was the ancestral state for amniotes and GSD evolved independently in particular lineages, either as ZZ/ZW or XX/XY system. In some cases, the same ancestral autosomes were independently co-opted for the function of sex chromosomes. On the contrary, the "super sex-chromosome" hypothesis expects that the last common amniote ancestor had GSD, with sex chromosomes consisting at least partially of orthologs of avian Z and mammalian X chromosomes. These ancestral sex chromosomes are assumed to be subsequently fragmented due to chromosomal fissions during the amniote evolution forming sex chromosomes in particular amniote lineages, or disappeared several times in ESD lineages.
The aim of the Ph.D thesis is to investigate the evolution of sex determining modes and the transitions among reptilian lineages in a wide phylogenetic scale, to reconstruct the evolution of sex chromosomes and their homology based on their gene content and to test evidence for the alternative hypotheses on the evolution of sex determination in amniotes (e.g. whether homology of sex chromosomes/independent co-option could be favorite due to similarities in gene expression). The successful candidate will collaborate with the other team members, conducting his/her research in a multidirectional approach involving classical and molecular cytogenetic (e.g., FISH, chromosome painting), molecular genetic (e.g., qPCR), genomic and bioinformatic methodologies (e.g., mRNA-seq, ddRAD-seq). This project will greatly enhance our knowledge on the fundamentals of sex differentiation and enable the unprecedented test of general hypotheses on the evolution of sex chromosomes.