A model of the evolution of the unusual sex chromosome system of Microtus oregoni

Heredity (Edinb). 2001 Apr;86(Pt 4):387-94. doi: 10.1046/j.1365-2540.2001.00803.x.


In the creeping vole, Microtus oregoni, females are X0 and males are XY. In the female germ line, mitotic nondisjunction ensures that the products of meiosis all carry the X chromosome. Similarly, mitotic nondisjunction in the male germ line leads to the production of 0 and Y sperm. We propose that the present situation in M. oregoni has evolved by invasion of a normal XX/XY system by a mutant X chromosome, X', with a complete transmission advantage in X'X females, and a complete transmission disadvantage in X'Y males. X' is at best initially nearly neutral, but can gain a transmission advantage if it reaches a high enough frequency. This is due to the production of X0 females in matings between XX females and X'Y males; low fertility and embryo loss of such females reduce the fitness of the X chromosome in females, relative to that of X'. Under some conditions, however, the enhanced reproductive value of males, caused by the production of inviable Y0 embryos in X0 x X'Y matings, can outweigh any advantage to X'. Inbreeding also reduces any advantage to X'.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Arvicolinae / genetics*
  • Biological Evolution*
  • Female
  • Genetics, Population
  • Male
  • Models, Genetic
  • Mutation
  • Sex Chromosomes*
  • X Chromosome
  • Y Chromosome