Sex chromosome aneuploidy in wild small mammals.

We describe four examples of the XO condition in wild mammals. One XO house mouse (Mus musculus domesticus) was caught in nature and subsequently gave birth to three litters in captivity, confirming for wild mice the fertility observed for XO laboratory mice. Two other XO house mice were produced from laboratory crosses of wild-caught mice. An immature XO common shrew (Sorex araneus) was caught in nature; this appears to be the first XO recorded in the order Insectivora. We collected data from researchers studying chromosome variation in house mice and common shrews and found an overall incidence of 0.22% sex chromosome aneuploidy in 4608 mice and 0.05% in 6625 shrews. The discrepancy related to a much higher frequency of XO's in mice than shrews. Single XXY and XYY shrews and an XXX mouse have been recorded in nature.