Inversions Are Bigger on the X Chromosome

Mol Ecol. 2019 Mar;28(6):1238-1245. doi: 10.1111/mec.14819. Epub 2018 Aug 29.


In many insects, X-linked inversions fix at a higher rate and are much less polymorphic than autosomal inversions. Here, we report that in Drosophila, X-linked inversions also capture 67% more genes. We estimated the number of genes captured through an approximate Bayesian computational analysis of gene orders in nine species of Drosophila. X-linked inversions fixed with a significantly larger gene content. Further, X-linked inversions of intermediate size enjoy highest fixation rate, while the fixation rate of autosomal inversions decreases with size. A less detailed analysis in Anopheles suggests a similar pattern holds in mosquitoes. We develop a population genetic model that assumes the fitness effects of inversions scale with the number of genes captured. We show that the same conditions that lead to a higher fixation rate also produce a larger size for inversions on the X.

Keywords: evolution; population genetics; sex chromosomes.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anopheles / cytology
  • Anopheles / genetics
  • Chromosome Inversion / genetics*
  • Chromosome Mapping
  • Drosophila / cytology
  • Drosophila / genetics*
  • Evolution, Molecular*
  • Genetics, Population
  • Phylogeny
  • Polymorphism, Genetic
  • X Chromosome / genetics*