Estimating tempo and mode of Y chromosome turnover: explaining Y chromosome loss with the fragile Y hypothesis

Summary

Ingested 2026-04-21. 2 findings extracted and verified.

Findings worth citing

Finding 1 — In the suborder Polyphaga, distance-pairing Xy+ sex chromosomes lose the Y approximately 3.5 times less frequently than XY systems with a pseudoautosomal region, despite being entirely nonrecombining.

it is surprising that Xy+ systems lose their Y 3.5 times less frequently than XY systems with a PAR — p. 568

Why this is citable: This is the central empirical observation motivating the fragile Y hypothesis and is the specific quantitative comparison that downstream papers would cite when discussing the counterintuitive stability of highly degenerated Y chromosomes.

Counter / limitation: The rate estimate depends on phylogenetic inference from a sparse supermatrix and on the assumption that karyotype states evolve under the specified Markov model; taxa with rarely studied cytogenetics could bias state assignments.

Topics: fragile_y_hypothesis, sex_chromosome_evolution

Finding 2 — In Adephaga, Y chromosomes are gained and lost at equal rates of approximately 0.57 events per 100 million years, and at least 49% of Y chromosome gains co-occur with reductions in autosome number consistent with X-autosome fusions.

For Adephaga, we find that Y chromosomes are gained and lost at a rate of 0.573 6 0.00052 gains and losses per 100 million years — p. 566

Why this is citable: Provides a quantitative baseline rate of Y chromosome turnover in Adephaga (equal gain and loss rates of ~0.57 per 100 million years) and supports the claim that X-autosome fusions are a major route of novel Y chromosome origin, with at least 49% of gains co-occurring with autosome number reductions. Useful to cite for neo-sex chromosome origin studies in insects.

Counter / limitation: The 49% fusion co-occurrence estimate relies on stochastic character mapping of both sex chromosome state and chromosome number simultaneously; errors in either mapping propagate into the co-occurrence estimate, and the remaining ~51% of gains are unresolved between B-chromosome capture and partial autosome fusions.

Topics: sex_chromosome_evolution, karyotype_evolution, coleoptera

Read the paper

doi.org/10.1534/genetics.114.164269

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