Lin, Tao Fei Diao, Yun Won Kang, Jung Eun Lee, Jae Kyo Kim, Dong Il Jin, Dong Morphological analysis identifies five categories of porcine first polar bodies. <p>Grade 1: Round or ovoid PB1 with intact smooth membrane (A). Grade 2: Round or ovoid PB1 with intact membrane (B). Grade 3: Broken PB1 with a small PB1 fragment (C). Grade 4: Broken PB1 with a big PB1 fragment (D). Grade 5: Broken PB1 completely (E). Grade 1, 2 were considered as good quality. Black arrows: Polar bodies. White arrows: Fragments. </p> identifies;categories;porcine;polar 2013-12-03
    https://plos.figshare.com/articles/figure/_Morphological_analysis_identifies_five_categories_of_porcine_first_polar_bodies_/867567
10.1371/journal.pone.0082766.g001