Ovaries of ewes homozygous for the X-linked Inverdale gene (FecXI) are devoid of secondary and tertiary follicles but contain many abnormal structures.

Ewes homozygous (II) for the Inverdale prolificacy gene (FecXI) located on the X chromosome are infertile with "streak" ovaries. The aims of this study were to examine the ovarian morphology and plasma and tissue (or extracellular fluid) hormone concentrations in II ewes in comparison to control (++) animals. All II animals (n = 11) were found to contain no normal ovarian follicles beyond the primary stage of development despite their being similar in number of germ cells to the ++ ewes. The II animals had high plasma gonadotropin levels and undetectable estradiol and progesterone, and in addition 6 of 9 ewes had undetectable plasma inhibin concentrations. II ewes contained large numbers of oocyte-free follicles ("nodules") that were often found as clusters in the innermost regions of the cortex. In addition, 6 of 11 ewes contained abnormal luteal- or granulosa cell-like structures and other unusual formations. In three II animals the abnormal structures were visible on the ovarian surface, and the plasma inhibin concentrations in these ewes were significantly higher than in the ++ ewes (p < 0.05). Collectively these findings suggest that two copies of the FecXI mutation impair the resumption of growth of primordial follicles and may in some instances lead to the development of abnormal structures having a morphology consistent with that observed for ovarian tumors.