Some characteristics of the XO mouse (Mus musculus L.) II. Reproduction: fertility and gametic segregation

A preliminary investigation of reproductive capacity in XO mice showed that they produced smaller litters than normal litter mates. More time elapsed between successive litters when kept in the presence of a male except during pregnancy and weaning. This lower level of reproduction is manifest during the whole reproductive period. Also reproductive capacity in XO mice reaches its maximum and minimum (end of reproductive period) earlier than in normals.Further study also demonstrated an underdevelopment of the ovaries-the whole ovary, as well as the numbers of maturing and mature follicles, are smaller in XO mice than in controls. Since these differences can be corrected by unilateral ovariectomy, they appear to be under control of extra-ovarial factors, e.g. of gonadotropic hormone(s). The data also suggest depression of activity in the oestrogen-producing system, and in general that the lower reproductivity of XO mice may be attributed to a diminished secretion of gonadotropic hormones together with a smaller number of primordial germ cells in XO mice.The segregation from XO parents seems to favor transmission of X-gametes in young mothers, with however the preference for X tending to decrease with parental age. Since the data tend to rule out postzygotic selection effects, the excess of X-bearing gametes may relate to meiotic drive.