Y chromosome instability in the early mouse embryo.

Early mouse embryonic mitoses show an unusually weak Y centromere, impairing kinetochore strength and causing preferential Y trapping at the spindle pole and missegregation.

• Why it matters: Although Y centromere weakness in adults is linked to Y loss and disease, its role during embryogenesis is unknown, limiting understanding of early aneuploidy origins.
• What they did: The study mapped Y centromere strength in the first mouse embryonic mitoses and used an aggregation model to track specific aneuploidies in mosaic embryos after Y loss.
• The result: Y loss slows cell division and compromises embryo size, revealing a developmental window when the Y is especially vulnerable, with implications for male sex determination and Turner syndrome (XO).

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