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Cracking the meiotic secrets behind animals asexuality When cytology seduces genomics to decode asexual meiosis.
J Evol Biol.
Asexuality is a derived character, and asexual species have emerged multipletimes independently throughout evolution. In animals, parthenogenesis, whereby azygote inherits only its mother genome, requires female meiosis modification toproduce unreduced gametes and compensate for the lack of outcrossing. Variouschanges in the meiotic steps have been identified. Here, we propose a simplifiednomenclature when discussing asexuality in animals, as the existing terminologyhas caused many misinterpretations and may impede interdisciplinarycollaboration. We also shed light on the constraints related to these meioticmodifications in asexual animals and their consequences on their genome. Whenrecombination is preserved in parthenogens, most meiotic modifications should,according to Mendel's second law, result in a loss of heterozygosity (LOH). Onthe other hand, LOH can be prevented if recombination is either abolished orstrongly reduced during meiotic prophase. Surprisingly, several recent exampleshave demonstrated that LOH can be prevented despite recombination. We willdescribe these examples in detail as they illustrate the constraints underlyingthe origin and evolution of asexuality. We also emphasize that the majority ofmechanisms remain unknown in many species. This highlights the need to revisitthe old literature using state-of-the-art cytological imaging and genomictechniques to shed light on these unexplored processes.
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