Some characteristics of the XO mouse (Mus musculus L.) I. Vitality: Growth and metabolism

The growth rate of XO mice during the first five weeks of life was shown to be significantly lower (ca. 15%) than the growth rate of normal XX mice. A marker gene Tabby was introduced in order to recognize hemizygous XO females. The presence or absence of this gene had a significant influence on growth rates. XO females could only be compared to XX females in an indirect way. The differences found could not be attributed to maternal influence or to the influence of litter size.Body temperature and thyroid activity were found to be lower in XO mice than in normal females. It is suggested that the lower growth rate characteristic of the XO mice is a consequence of hypothyroidism and a lower basal metabolic rate.The results show that phenotypically XO mice are not entirely normal and at least two normal X's are necessary for complete development.