Figure 5.

Occurrence of achiasmate X chromosomes in him-6 mutant oocytes correlates with reduced crossover frequency during oocyte meiosis. (A) Each column shows the full karyotype of a single diakinesis oocyte from a him-6 mutant worm, with the X chromosomes visualized by chromosome paint. In the top two oocytes, the X chromosome pairs comprise a bivalent, whereas in the bottom oocyte, the X chromosomes clearly lack a chiasma and are present as univalents. (The different configurations of the red and green paint signals on the X chromosome bivalents in the top two images likely reflect different CO positions.) Scale bars, 5 μm. (B) Graph showing the genetic map distances measured for oocyte meiosis for the dpy-3 unc-3 interval on the X chromosome; error bars indicate 95% confidence intervals. Although the reduction in CO frequency in the tested interval in the him-6 mutant appears nominally higher than the incidence of achiasmate X chromosomes observed using the paint assay, based on the experimental error associated with both types of measurements, there is insufficient statistical power to conclude that this difference is significant. Thus, these data are not considered as part of the evidence for persistent connections between noncrossover chromosomes.