(A, B) Overview of a cold-treated meiotic spindle and examples of its bivalents in an oocyte from (A) a young (24 years old) and (B) an older (40 years old) donor. Scale bars represent 5 µm in overviews and 1 µm in examples. (C) Relative frequency of individual sister kinetochore pair distances across different age groups. 2,588 measurements were obtained from 57 oocytes. Distances between unresolvable sister kinetochore configurations of the indistinguishable and overlapping categories (as shown in (1B)) are presented as 0 µm. (D) Age-related increase in the incidence of separated sister kinetochores in 58 human oocytes. ****p≤0.0001. (E) Occurrence of kinetochore configurations defined in (1B) across different age groups. *p≤0.05, **p≤0.01, ***p≤0.001, ****p≤0.0001. Significance analyses were performed for changes relative to <30 years old age group. (F) Quantification of the proportion of microtubule attachments (shown in H) in each category of sister kinetochore configurations. *p≤0.05, **p≤0.01, ***p≤0.001 (Fisher’s exact test). Significance analyses were performed for changes in the frequency of merotelic (***) and lateral (*) attachment modes relative to the unified kinetochore group. (G) The proportion of kinetochore-microtubule attachments (shown in (H)) in cold-treated spindles of oocytes from each age group. N=25 oocytes. *p≤0.05, **p≤0.01, ***p≤0.001, ****p≤0.0001. Significance analyses were performed for changes in the frequency of merotelic attachment mode relative to <30 years old age group. (H) Representative maximum intensity z-projections of immunofluorescence images of cold-treated spindles showing different microtubule attachment types across the three categories of sister kinetochore configurations defined in (1B). Arrowheads indicate kinetochore pairs with the specified microtubule attachment type. Scale bar represents 5 µm in overview, 1 µm in insets.