Oocytes with unresolved DNA DSBs on the Z chromosome progress to diplotene.

<p>(A–F) 6 dph oocytes stained for RPA (red) and SYCP3 (green). The diplotene cells were classified as early when desynapsis was partial and late when desynapsis was complete. (A–B) Late pachytene; (C–D) early diplotene; (E–F) late diplotene. (A, C, E) Cells RPA negative (RPA^−ve), and (B, D, F) cells carrying a chain of RPA foci (RPA^+ve). (G) Graph showing the percentage of RPA^+ve cells at each stage. Total number of cells analysed: late pachytene, 141; early diplotene, 223; late diplotene, 169. ZW chromosome painting performed after antibody staining showed that the Z chromosome accounted for 85% of the RPA^+ve cells identified at pachytene and 74% at early diplotene, making the percentage of late pachytene ZW^RPA+ = 21.7% and the percentage of early diplotene ZW^RPA+ = 19.6%. The percentage of ZW^RPA+ pairs at late diplotene was not calculated as in many of these cells it was not possible to unambiguosly identify the entire Z axis. The quantification was done on ovaries from the chicken line ISA Brown. (H) 14 dph oocytes stained for RPA (red) and SYCP3 (green). 90% of the cells are negative for SYCP3; no RPA was identified in these cells (number of cells analysed: 60). Scale bar = 10 µm.