Cytogenetic analysis of mouse oocytes following in vitro exposure to MG-132, chromosome configurations are shown. (A) metaphase II oocyte, normal, n = 20 dyads. (B) metaphase I oocyte, normal, N = 20 tetrads. (C) metaphase II oocyte, hypoploid, premature centromere separation (incomplete), n = 19 1/2 (10 dyads and 19 chromatids), arrow points to one of the 19 single, unpaired chromatids. (D) metaphase II oocyte, hyperploid, n= 22 dyads. (E) metaphase II oocyte, hyperploid, single-unpaired chromatid, n = 20 1/2 (20 dyads and one single, unpaired chromatid indicated by arrow). (F) metaphase I oocyte, diffuse chromatin, N= 20 probable tetrads. (G) metaphase I oocyte, homologue separation, N= 20 (17 tetrads and 6 dyads), arrow points to one of the 6 dyads. (H) metaphase I oocyte, homologue separation, N= 19 1/2 (16 tetrads and 7 dyads).