Figure 2. Achiasmate Xs are observed on the same half of the spindle in fixed oocytes.

The number of oocytes with achiasmate Xs on the opposite or the same side of the meiotic spindle is shown as a fraction of the total number of oocytes examined with a representative image for both FM7/X and X/X oocytes. The number of scorable oocytes is considerably smaller for X/X oocytes since X chromosomes would be achiasmate in only 5–10% of oocytes. It is possible the two associated X chromosomes in the bottom right of the figure are actually chiasmate, but the morphology of the chromosomes indicate they are spontaneous achiasmate Xs. DNA was stained with DAPI. Arrowheads indicate the densely staining blocks of heterochromatin on the normal sequence X and FM7 that can be used to determine the orientation of the chromosomes.