Chromosome Dynamics and Evolution

Schematics of meiotic drive in female meiosis. Asymmetry in female meiosis provides unique opportunity for selfish centromeres to cheat. The spindle is positioned close to the cortex and orients perpendicular to the cortex. Centromeres (blue circles) interact with the spindle and direct chromosome segregation. Selfish centromeres (bigger blue circles) preferentially orient to the interior side of the spindle, which remains in the egg.

Cell biology of centromere drive. (A) Crossing different mouse strains generates a hybrid with a difference in centromeres within the bivalent. Larger centromeres with expanded satellite repeats act selfishly over smaller centromeres. (B) Spindle asymmetry depends on active CDC-42 at the polarized cortex. (C) A model for biased orientation of selfish centromeres. Orientation is initially random (i). However, selfish centromeres (bigger blue circles) preferentially destabilize MT attachments with the cortical side (green lines) and detach (ii), leading to biased flipping to the egg side (yellow lines), and biased orientation (iii).

Meiotic bivalents pairing homologous chromosomes from different species in inter-specific hybrid mouse oocytes

Spindle asymmetry (grey) induced by polarized cortex (green) serves as a spatial cue to guide selfish centromeres.

Meiotic drive of non-centromeric locus (green)

Selfish centromeres cheating in action!

Mouse oocyte cells extruding the polar body, which is an evolutionary dead end for chromosomes.