Figure 1. Fertilization with primary spermatocytes.

1. The scheme of construction of a diploid fertilized oocyte using a primary spermatocyte and a GV‐stage oocyte. The chromosomes of the spermatocyte and the oocyte are intermingled at MI to form a single chromosomal mass.
2. Spermatocyte chromosomes that underwent condensation (right) within a MII oocyte (MII chromosome mass, left). In this study, spermatocytes picked up for injection had tetrad chromosomes ready for condensation.
3. Chromosomal analysis of MII oocytes that had been injected with primary spermatocytes. In the spermatocyte‐injected groups, normality was improved by reducing the ooplasm mass (*P < 0.005 by Fisher’s exact probability test). Arrows in the right figure indicate prematurely separated chromatids. The numbers of oocytes observed are indicated on the top of the bars. For the exact numbers in each case, see also Appendix Table S1. PB, polar body; GV, germinal vesicle; MI, meiosis I; PN, pronuclear stage.