Insect sex chromosome evolution: Conservation, turnover, and mechanisms of dosage compensation Toups, Melissa A ; https://orcid.org/0000-0002-9752-7380 Vicoso, Beatriz ; https://orcid.org/0000-0002-4579-8306 ddc:570 Sex chromosomes have evolved many times throughout the tree of life, and understanding what has shaped their unusual morphological, sequence, and regulatory features has been a long-standing goal. Most early insights into insect sex chromosome biology came from a few model species, such as the fruit fly Drosophila melanogaster, which limited broad-scale evolutionary inferences. More recently, extensive comparative genomics studies have uncovered several unexpected patterns, which we highlight in this review. First, we describe the conservation of the ancestral X chromosome over 450 million years but also its recurrent turnover (i.e. its reversal to an autosome when a new X chromosome arose) in at least one order. We then summarize classical and more recent findings on how insects modulate the expression of X-linked genes following the degradation of the Y chromosome and how the diverse mechanisms of dosage compensation identified may elucidate important principles of sex chromosome regulatory evolution. Elsevier 2025 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_dcae04bc https://research-explorer.ista.ac.at/record/20182 https://research-explorer.ista.ac.at/download/20182/20917 Toups MA, Vicoso B. Insect sex chromosome evolution: Conservation, turnover, and mechanisms of dosage compensation. <i>Current Opinion in Insect Science</i>. 2025;72. doi:<a href="https://doi.org/10.1016/j.cois.2025.101411">10.1016/j.cois.2025.101411</a> eng info:eu-repo/semantics/altIdentifier/doi/10.1016/j.cois.2025.101411 info:eu-repo/semantics/altIdentifier/issn/2214-5745 info:eu-repo/semantics/altIdentifier/e-issn/2214-5753 info:eu-repo/semantics/altIdentifier/wos/001582424100001 https://creativecommons.org/licenses/by/4.0/ info:eu-repo/semantics/openAccess