Figure 2. (A–D) Representative maximum projection of chromosome spreads for euploid and aneuploid MII oocytes from young and old mares. Green, kinetochores (CREST); blue, chromatin (Hoechst). (a–d) explanatory drawing of the chromosome spreads. Different sister chromatid pairs have different colors. For the chromatids colored in red, it was not possible to distinguish single pairs and they were therefore used only for ploidy assessment and not for interkinetocore distance measurement. A total of 64 CREST positive foci (32 pairs of sister chromatid kinetochores) are shown in an euploid MII oocyte from a young mare (A) and an old mare (B). (C) A total of 63 CREST positive foci are displayed in an aneuploid MII oocyte from an old mare; the white arrow indicates an uneven and unpaired kinetochore. (D) A total of 60 CREST positive foci are seen in an aneuploid MII oocyte from an old mare; the arrow head indicates an unpaired kinetochore. Bar, 5μm.