Fig. 1.

The defining features of meiotic drive in asymmetric and symmetric meiosis. a Females undergo asymmetric meiosis—a single gamete is produced from a single round of meiosis. The driving cis-acting chromosomes (dark pink) biases its retention to the egg by interacting with the inward-facing egg pole (green arrow). The non-driving chromosome (light pink) binds the outward facing cortical pole and is extruded to a polar body (red arrow) which is degraded (red X). * The second polar body is extruded upon fertilization. b Males undergo symmetric meiosis—four gametes are produced from a single round of meiosis. Male meiotic drive systems bias fertilization by increasing the relative abundance of sperm carrying the driving chromosome (green arrow), or by decreasing the fitness of sperm with the non-driving chromosome (red arrow). Gray mRNA and protein represent X-linked trans-acting factors which remain in X-bearing cells (e.g., intracellular). Green mRNA and protein represent X-linked trans-acting factors which are shared and present in Y-bearing cells (e.g., intercellular) via cytoplasmic bridges. Cytoplasmic bridges are established prior to meiosis, in spermatogonia, and connect cells throughout meiosis and after meiosis. For simplicity, a single meiotic cell and the products of meiosis are shown.