Open AccessA model of the evolution of the unusual sex chromosome system of Microtus oregoni
Author(s) -
Charlesworth B.,
Dempsey N. D.
Publication year - 2001
Publication title -
heredity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.441
H-Index - 118
eISSN - 1365-2540
pISSN - 0018-067X
DOI - 10.1046/j.1365-2540.2001.00803.x
Subject(s) - biology , nondisjunction , x chromosome , meiosis , chromosome , genetics , y chromosome , ploidy , embryo , microtus , aneuploidy , zoology , gene
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′Y matings, can outweigh any advantage to X′. Inbreeding also reduces any advantage to X′.