During the early stages of meiosis, homologous chromosome pairs stick together in a structure called a bivalent. This structure is held together using protein complexes called cohesins, which tend to decrease with age to potentially lead to errors in meiosis and aneuploidy. The bivalent structure is the configuration of chromosomes in eggs before they enter the menstrual cycle (in prophase of meiosis I), which can potentially last for decades.
