• mice exhibit greater thickening and hyperplasia of peritubular myoid cells compared to Ar^Tfm male mice on the original stock background

• unlike Ar^Tfm male mice on the original stock background

• in 8 of 31 mice unlike Ar^Tfm male mice on the original stock background

• compared to Ar^Tfm male mice on a mixed NMRI and stock of origin background

• spermatogenesis does not proceed beyond meiosis prophase

• male mice have female genitals, a blind ending vagina, inguinal testes, no scrotum and lack derivatives of the Wolffian ducts

• 3 of 31 mice exhibit unilateral Leydig tumor unlike Ar^Tfm male mice on the original stock background

• however, no germ cell tumors are observed

• mice exhibit greater thickening and hyperplasia of peritubular myoid cells compared to Ar^Tfm male mice on the original stock background

• unlike Ar^Tfm male mice on the original stock background

• in 8 of 31 mice unlike Ar^Tfm male mice on the original stock background

• compared to Ar^Tfm male mice on a mixed NMRI and stock of origin background