article epub_ahead yes Lorena Alexandra Layana Franco author 02814589-eb8f-11eb-b029-a70074f3f18f0000-0002-1253-6297 Melissa A Toups author 4E099E4E-F248-11E8-B48F-1D18A9856A870000-0002-9752-7380 Beatriz Vicoso author 49E1C5C6-F248-11E8-B48F-1D18A9856A870000-0002-4579-8306 BeVi department GradSch department Sex chromosomes in evolution and development project Sex-chromosome systems are highly variable across animals, but how they transition from one to another is not well understood. Diptera have undergone multiple sex-chromosome turnovers and expansions while maintaining their general chromosomal content, which makes them an ideal clade to study such transitions. We analyzed more than 100 dipteran whole-genome assemblies and identified 4 new lineages that underwent sex-chromosome turnover (in addition to the 5 previously reported). We find that the majority of turnovers happened in the group Schizophora, which tend to have fewer genes on Muller element F (the chromosome homologous to the ancestral insect X chromosome) than lower dipterans, a factor previously hypothesized to facilitate turnover. Most derived X chromosomes have higher GC content than autosomes, consistent with a high prevalence of male achiasmy in Diptera. In addition, an excess of gene movement out of the X is detected for most of these new X chromosomes, and many of these moved genes have high testis expression in Drosophila, suggesting that out-of-X gene movement contributes to the long-term demasculinization of X chromosomes. Oxford University Press2026 eng 2056-374410.1093/evlett/qrag003 L. A. Layana Franco, M. A. Toups, and B. Vicoso, “Causes and consequences of sex-chromosome turnovers in Diptera,” <i>Evolution Letters</i>. Oxford University Press, 2026. Layana Franco, Lorena Alexandra, et al. “Causes and Consequences of Sex-Chromosome Turnovers in Diptera.” <i>Evolution Letters</i>, qrag003, Oxford University Press, 2026, doi:<a href="https://doi.org/10.1093/evlett/qrag003">10.1093/evlett/qrag003</a>. Layana Franco, Lorena Alexandra, Melissa A Toups, and Beatriz Vicoso. “Causes and Consequences of Sex-Chromosome Turnovers in Diptera.” <i>Evolution Letters</i>. Oxford University Press, 2026. <a href="https://doi.org/10.1093/evlett/qrag003">https://doi.org/10.1093/evlett/qrag003</a>. Layana Franco, L. A., Toups, M. A., &#38; Vicoso, B. (2026). Causes and consequences of sex-chromosome turnovers in Diptera. <i>Evolution Letters</i>. Oxford University Press. <a href="https://doi.org/10.1093/evlett/qrag003">https://doi.org/10.1093/evlett/qrag003</a> L.A. Layana Franco, M.A. Toups, B. Vicoso, Evolution Letters (2026). Layana Franco LA, Toups MA, Vicoso B. Causes and consequences of sex-chromosome turnovers in Diptera. <i>Evolution Letters</i>. 2026. doi:<a href="https://doi.org/10.1093/evlett/qrag003">10.1093/evlett/qrag003</a> Layana Franco LA, Toups MA, Vicoso B. 2026. Causes and consequences of sex-chromosome turnovers in Diptera. Evolution Letters., qrag003. 214862026-03-23T15:05:42Z2026-03-24T07:14:08Z