The structure and evolution of sex chromosomes in an androdioecious species with two mating types.

In Phillyrea angustifolia, the XY sex-determining region spans one fifth of chromosome 12 and is larger and more rearranged than in Phillyrea latifolia.

• Why it matters: Androdioecy’s unusual male frequency depends on how males bypass hermaphrodite self-incompatibility, but the molecular sex determinants and their evolutionary history were unknown.
• What they did: The study generated full haplotype-resolved de novo chromosomal assemblies for P. angustifolia and P. latifolia, then mapped the sex region and identified candidate genes and expression-linked loci.
• The result: The male-specific region contains ANDY1 and ANDY2 and a recent duplicate of Ole-e1, which shows the strongest differential expression between hermaphrodite self-incompatibility groups, linking sex and self-incompatibility.

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