A) Metaphase II oocytes from mice carrying a conditional, oocyte-specific invalidation of separase (Separaseflox/flox Zp3 Cre+, or Sep-/-) and oocytes from litter mates (Separaseflox/flox, or Sep+/+) were obtained after superovulation. In vivo matured control (Sep+/+) and Sep-/- oocytes are found in oviducts at comparable numbers, enclosed by cumulus cells. Example of cumulus enclosed oocytes from the oviduct is shown below. In (A), n indicates the number of mice and a mean number of oocytes per mouse of each genotype, error bars are + s.e.m. 