Diplotene stage

All primary oocytes are already present about a week before birth. Many of these remain in an arrested diplotene stage of meiosis for many months before ovulation or loss by atresia. Stages of primary oocyte development are defined by the cytologic appearance of the oocyte and its follicle. 

Figure 26-13 Synaptonemal complexes. (A) Aligned pairs of homologous chromatids lying 0.4 pm apart in Allium cepa. Arrows indicate "recombination nodules" which may be involved in initiating formation of crossovers. Portions of meiotic chromosomes of lily are shown at successive stages (B) Pachytene. (C) Portion of diplotene nucleus. (D) A bivalent at diplo-tene. (E) Two bivalents at diakinesis. Pairs of sister chromatids are coiled with appropriate handedness. (F) Sister chromatid cores are far apart in preparation for separation. A chiasma is present between the two central strands. (B) through (F) courtesy of Stephen Stack.279,279d (G) Pair of sister chromatids coiled with opposite handedness at metaphase. These are immun-ostained with anti-topoisomerase II antibodies. From Boy de la Tour and Laemmli.280 Courtesy of U. K. Laemmli.

Because the germ cell stage of longest duration in the female mouse and human is the arrested diplotene oocyte, this might appear to be the stage of maximal hazard in... 

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