The origination events of gametic sexual reproduction and anisogamy

Abstract The evolution of gametic sex (meiosis and fertilization) subsequent transition from isogamy (fusion between two equal-sized gametes) to anisogamy (dimorphism into eggs sperm, namely, females males) is one the largest enigmas evolutionary biology. Meiosis entails genome-dilution cost male-production cost. Despite much progress has been made for maintenance mechanisms sex, its origination events under such “twofold sex” are still unsolved. Here, we posit hypothetical scenarios as follows: “Seesaw Effect” hypothesizes that automictic selfing isogametes effectively purged deleterious mutations an organism’s lineage simultaneously fixed sex-controlling allele all other loci (no raised). high relatedness among homoeologous cell colonies led multicellularization. “inflated isogamy” multicellularity increased reproductive investment both mates, resulting in excessively large isogametes. This redundancy induced cheating (evolving male) reduce gamete size. However, female) allowed this cheat because her did not change. Therefore, originated a kind commensalism but turned beneficial it solved limitation problem inherent isogamy. Thus, smooth had attained.