Abstract
Publisher Summary This chapter focuses on recent advances in the knowledge of genes and gene functions that may regulate displacement of meiosis, heterochronic or ectopic development of embryo sacs, and spontaneous formation of embryos from egg cells, which are observed in natural apomicts or predominantly in mutants from sexual species. Apomixis is the process of asexual reproduction through seeds that is increasingly being viewed as a deregulation of sexual reproduction rather than an independent pathway. It includes both sporophytic and gametophytic types. Somatic cells of the ovule directly form embryos during sporophytic apomixis. Gametophytic apomixis is characterized by the formation of an unreduced embryo sac and parthenogenesis of the unreduced egg. Universal differences between the two modes of reproduction are discussed, which includes the origin or developmental state of cells specified to become embryo sac mother cells and egg activation in the absence of fertilization. Gametophytic apomicts are broadly classified as either aposporous or diplosporous. Chromosomally unreduced embryo sacs develop from an megaspore mother cell (MMC) or a nearby nucellar cell.
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