A light- and electron microscopic analysis of meiotic prophase in female mice.

In the paper we describe meiotic prophase of female mice on successive days of embryonic and early postnatal development. For this purpose we used three different techniques on ovarian material, i.e., Giemsa staining for the light microscopic study of chromatin, silver staining for the light microscopic study of the synaptonemal complex (SC), and agar filtration followed by uranyl acetate staining for the electron microscopic study of the SC. In all types of preparation it was impossible to distinguish leptotene stages, and we conclude that if leptotene really exists, it is of very short duration.--Two types of zygotene stages were found: the "normal" one, resembling zygotene stages in male mice, and a second type that has never been described in males and is characterized by, probably stable, unpaired regions together with totally unpaired axial elements of the SC.--The duration of pachytene was found to be 3-4 days, which is considerably shorter than in males. During early diplotene despiralization of the chromatin and disintegration of the axes of the SC were usually found together with desynapsis.--A considerable variation in distribution of meiotic stages was found between different litters in the same day of gestation. Fetuses in the same litter showed no significant variation. However, the oocytes in an ovary did not pass through meiosis synchronously, with differences up several days. The appearance of chromosomes in a highly contracted state could not be interpreted as a preleptotene condensation stage but probably is a mitotic phenomenon.