Introduction

Because the laboratory mouse has been used so widely in biological research, it will come as little surprise to learn that abnormalities have been observed throughout the reproductive system, not least in inbred strains of mice. These abnormalities extend from an absence of functional gonads to the formation of hermaphrodites in which ovotestes are observed unilaterally or comprising both gonads. The origin of such conditions would appear to reside in spontaneously arising mutant genes. Experimentally generated mice such as chimaeras or transgenics also demonstrate a variety of reproductive abnormalities, and highlight the apparent vulnerability of gonadal and genital tissues to major derangement expressed as modification of structure. Even so, derangement that involves generation of both male and female tissue within the same gonad immediately raises questions concerning sex determination and differentiation. For such a situation to arise, it would seem possible to argue that the downstream gene programmes for testicular and ovarian development are both present in mammalian zygotes, and that sex determination involves active suppression of one of the programmes, a step prompted by a gene located on a sex chromosome. An inappropriate or untimely instigation or regulation of the suppression mechanism could permit generation of an ovotestis.

The objective of this chapter is to comment on some of these abnormal conditions, and to introduce concepts that will be relevant to the ensuing chapter dealing with man.