Despite the sex differences in the stage and degree of meiotic disturbances, the cause of these disturbances is probably the same. This is failure of a homologous synapsis between homologous chromosome regions, which is complete in males and partial and sporadic in females. The majority of oocytes contains multiple regions of asynapsis and non-homologous synapsis. The establishment and extension of non-homologous synapsis leads to multivalent and univalent formation. Thus, when one homologue is involved in a multivalent, the other either remains univalent or pairs non-homologously with another chromosome region in the same or a different multivalent.