Sylvia Kinosian , Michael S Barker

Meiotic drive is a deviation from Mendelian inheritance where genetic elements are preferentially inherited by the surviving egg cell. This can profoundly impact chromosome (and genome) size and structure. Across vascular plants, heterosporous lineages typically have fewer chromosomes than homosporous lineages. The underlying mechanism causing this disparity has been debated for over half a century. Although reproductive mode has been identified as critical to these patterns, the symmetry of meiosis during sporogenesis has been overlooked as a cause of the difference in chromosome numbers. In most heterosporous plants, meiosis during megasporogenesis is asymmetric, meaning one of the four meiotic products survives to become the egg, and the three polar bodies die. Comparatively, meiosis is symmetric in homosporous megasporogenesis and all meiotic products survive. The symmetry of meiosis is important because asymmetric meiosis enables meiotic drive and associated genomic changes. Here we review how meiotic drive impacts genome evolution, what we would expect to see in lineages without meiotic drive, and finally what the first homosporous plant genomes tell us about patterns of evolution concerning meiotic drive.