Abstract For a long time, snakes were presented as a textbook example of a group with gradual differentiation of homologous ZZ/ZW sex chromosomes. However, recent advances revealed that the ZZ/ZW sex chromosomes characterize only caenophidian snakes and certain species of boas and pythons have non-homologous XX/XY sex chromosomes. We used genome coverage analysis in four non-caenophidian species to identify their sex chromosomes, and we examined the homology of sex chromosomes across phylogenetically-informative snake lineages. We identified sex chromosomes for the first time in 13 species of non-caenophidian snakes, providing much deeper insights into the evolutionary history of snake sex chromosomes. The evolution of sex chromosomes in snakes is more complex than previously thought. Snakes may have had ancestral XX/XY sex chromosomes, which are still present in a blind snake and some boas, and there were several transitions to derived XX/XY sex chromosomes with different gene content and two or even three transitions to ZZ/ZW sex chromosomes. However, we discuss more alternative scenarios. In any case, we document that (1) some genomic regions were likely repeatedly co-opted as sex chromosomes in phylogenetically distant lineages, even with opposite types of heterogamety; (2) snake lineages differ greatly in the rate of differentiation of sex chromosomes; (3) snakes likely originally possessed sex chromosomes prone to turnovers. The sex chromosomes became evolutionarily highly stable once their differentiation progressed in the megadiverse caenophidian snakes. Snakes thus provide an ideal system for studying the evolutionary factors that drive unequal rates of differentiation, turnovers and stability of sex chromosomes.

Tomáš Pšenička

Barbora Augstenová

Daniel Frynta

Panagiotis Kornilios

Lukáš Kratochvíl

Michail Rovatsos

Molecular Biology and Evolution

MOLECULAR BIOLOGY AND EVOLUTION 在分子（包括基因组学）和进化生物学的界面发表研究。我们考虑包含人口、分类、功能和表型组织各个层次的模式、过程和预测的手稿。除了具有更广泛范围和影响的基本发现外，我们还对出版新的和改进的方法、资源、技术和理论感兴趣，这些方法、资源、技术和理论将显着推进进化研究。我们还发表了对基因组进化最新发展的平衡评论和前瞻性观点，提出了分子进化领域或应用的未来方向。

The journal "Molecular Biology and Evolution" focuses on the interface of molecular biology and evolutionary biology, publishing research in this area. We welcome manuscripts that address patterns, processes, and predictions across various levels, including population, taxonomy, function, and phenotype. In addition to fundamental findings with broad implications, we are also interested in publishing new and improved methods, resources, technologies, and theories that significantly advance evolutionary research. Furthermore, we publish balanced reviews and forward-looking perspectives on the latest developments in genome evolution, proposing future directions for the field of molecular evolution and its applications.

《Molecular Biology and Evolution》期刊专注于分子生物学与进化生物学的交叉领域，发表相关研究成果。我们欢迎涉及种群、分类、功能和表型等多个层面的模式、过程和预测的手稿。除了具有广泛影响的基础研究发现外，我们也对新的和改进的方法、资源、技术和理论感兴趣，这些内容将显著推动进化研究的发展。此外，我们还发表关于基因组进化最新进展的综合评论和前瞻性观点，探讨分子进化领域及其应用的未来方向。

Category	Quartile
生物学	1
生物学, 遗传学	1
生物学, 生化与分子生物学	2
生物学, 进化生物学	2

Sex chromosome turnovers and stability in snakes

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Category	Quartile
GENETICS & HEREDITY	1