Evolution: Shape-shifting vole sex determination and sex chromosomes

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It has long been known that some mouse and vole species have unusual sex chromosomes, and this new genome sequencing study advances understanding of a particularly puzzling vole system.

Most mammals studied, across a wide diversity of taxa, share an XX female, XY male sex chromosome system (Figure 1A). Their X chromosomes carry largely similar sets of genes, although only part of the X in Eutherians is homologous to the Marsupial X, (part was a Marsupial autosome that was added later). The Y chromosomes of both Marsupials and Eutherians are non-recombining, and have lost almost all genes ancestrally carried on this chromosome. Only ten X-linked genes have homologues on the Ys of many Eutherians, indicating that these “ancestrally Y-linked genes” have long been evolving independently of their X counterparts. Their sequences are so diverged from their X-linked alleles that these allele pairs have been termed “gametologs”. The sex-determining system is also similar across most Eutherian lineages [1]. The so-called “mammalian master sex-determining gene” or male determiner, SRY (the gametolog of the X-linked SOX3 gene) includes a region encoding an “HMG box” that activates a regulatory network leading the gonad to develop as a testis. However, very strange things have happened in some mouse and vole species. In Microtus oregoni, the species in this new study [2], genome sequence data are providing new details that may help understand its differences from other mammals.
Original languageEnglish
Pages (from-to)PR967-R969
Number of pages3
JournalCurrent Biology
Issue number15
Publication statusPublished - 9 Aug 2021


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