Fig. 8.

Model for the generation of single chromatids following maternal aging. The effect of maternal aging is depicted on a bivalent (dark and light grey) during meiosis I (MI) and entry into meiosis II (MII). Aging is associated with a loss of cohesin and SGO2, which results in centromeric cohesion loss at anaphase. However, the two single chromatids co-segregate normally because they are attached to the same pole. When attachment of microtubules (green) is established following exit from interkinesis, the two single chromatids no longer are able to maintain their cohesion, and attach independently to microtubules. They are therefore subject to random segregation in MII, as opposed to the normal equational segregation, and consequently are liable to generate aneuploid embryos.