Chromosomes were studied in DBN2N mouse oocytes after superovulation.
Twenty female mice were divided into 2 groups. Group I animals were induced to superovulate
by injections of 5 IU PMSG and 5 IU hCG, and group II animals were injected with 10 IU
PMSG and 10 IU hCG. Two cases of chiasma were found among the oocytes in group II. The
rest of oocytes showed normal chromosomes in metaphase II. These results demonstrated that
PMSG and hCG-induced superovulation correlated with chiasma formation