The Biology of Reproduction

Skipping sex: A nonrecombinant genomic assemblage of complementary reproductive modules

“…Sometimes, asexuals do not require mating and in all cases, eggs develop either without fertilization or fusion of female and male nuclei. [24,35,36] Of note, the pathways of egg development vary among asexuals.…”

“…[37] Hence, automixis creates endogamous recombinant offspring without male contribution and leads to homozygosity. [35,36,38,39] In gynogenetic and parthenogenetic species (including apomictic plants), meiosis is skipped and unreduced gametes carrying the maternal genetic information develop into new clonal individuals by parthenogenesis. While gynogenesis require mating and/or fertilization (without fusion of female and male nuclei) to trigger embryogenesis, parthenogens develop spontaneously.…”

“…While gynogenesis require mating and/or fertilization (without fusion of female and male nuclei) to trigger embryogenesis, parthenogens develop spontaneously. [36,[39][40][41] In hybridogenetic species, paternal chromosomes are eliminated during female meiosis and reduced gametes carry only maternal chromosomes. Such gametes require fertilization by a male gamete to develop a new individual.…”

“…However, during the formation of the next generation, those individuals only transmit the maternal genetic information to the offspring. [36,41,42]…”

“…Variable levels of heterozygosity are expected in automicts depending upon the number of crossovers per chromosome arm and generation, the genome size, and the type of gamete fusion. [35,36] Jumping from an automictic (likely highly homozygous) development to a sexual one or one of the clonal alternatives might be triggered by a hybridization event, perhaps reinforced by a ploidy shift. This would explain cases of gain of sexuality in some automictic species [110,111] and provide a reason for most automicts being diploids and the clonal asexual alternatives being of hybrid or polyploid origin.…”