Long-Term Fragility of Y Chromosomes Is Dominated by Short-Term Resolution of Sexual Antagonism.

Summary

Ingested 2026-04-21. 3 findings extracted and verified.

Findings worth citing

Finding 1 — Y chromosome inversions linking a male-beneficial allele to the SDR can fix even when they increase aneuploidy by 4-6%, provided the male-beneficial allele is dominant and selection is at least s≈0.2.

For instance, if the male-beneficial allele is dominant a selection coefficient as small as 0.2 is sufficient to fix Y chromosome inversions that increase aneuploidy by ∼4–6%

Why this is citable: This is the paper’s central quantitative claim: it defines the parameter regime in which sexually antagonistic inversions overcome the aneuploidy cost on the Y, grounding the ‘long-term fragility from short-term resolution’ thesis.

Counter / limitation: The result comes from a deterministic three-locus model with symmetric fitness effects and a fixed multiplicative aneuploidy cost; empirical aneuploidy-PAR relationships and drift are not modeled, so the quantitative threshold may not translate directly to real populations.

Topics: sex_chromosome_evolution, fragile_y_hypothesis, sex_linkage_mutation

Finding 2 — X chromosome inversions capturing a female-beneficial allele cannot fix when the male-beneficial allele is recessive (h < ~0.3) and instead are maintained as stable polymorphisms.

When the male-beneficial allele is recessive (h < 0.3), an X chromosome inversion that captures the female-beneficial allele cannot fix, and instead is maintained as a stable polymorphism

Why this is citable: Identifies a specific genetic-architecture regime that generates balanced polymorphism on the X, relevant to claims about the X as a hotspot for sexually antagonistic variation.

Counter / limitation: The threshold h≈0.3 is model-specific, assumes symmetric sex-specific fitness effects and full recombination suppression by the inversion, and ignores drift that could destabilize polymorphisms at low frequency.

Topics: sex_chromosome_evolution, sex_linkage_mutation

Finding 3 — The fate of sexually antagonistic inversions depends on the recombination rate between the SDR and the SA locus, with higher background recombination permitting inversions with larger aneuploidy costs to fix, especially on the Y.

a given selection coefficient allows inversions with larger aneuploidy cost to fix as the recombination rate increases. This is more pronounced in Y chromosome inversions than it is in X chromosome inversions. In the case of X chromosome inversions, recombination rates of >0.3 provide little additional benefit to inversions

Why this is citable: Shows that larger background recombination rates between the SDR and SA locus increase the selective advantage of inversions, allowing inversions with greater aneuploidy costs to fix—an effect that is stronger for Y than X chromosome inversions and saturates for X inversions above r>0.3. This supports the paper’s broader argument about how PAR size and recombination dynamics shape sex chromosome evolution.

Counter / limitation: The model treats recombination rate as an independent parameter rather than deriving it from explicit PAR size; the paper itself notes that ‘before we can make strong predictions about the expected distribution of inversion sizes, we must know the relationship between aneuploidy risk and PAR size,’ so the link between recombination rate and inversion size distribution remains qualitative and lineage-specific.

Topics: fragile_y_hypothesis, sex_chromosome_evolution

Read the paper

doi.org/10.1534/genetics.117.300382

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