Biodiv Sci ›› 2016, Vol. 24 ›› Issue (8): 966-976.  DOI: 10.17520/biods.2016057

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How did nucleus and sexual reproduction come into being?

Ping Xie*()   

  1. Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072
  • Received:2016-02-28 Accepted:2016-07-12 Online:2016-08-20 Published:2016-09-02
  • Contact: Xie Ping


The origin of eukaryote is a fundamental, forbidding evolutionary puzzle, and the popular scenarios of eukaryogenesis are far from being clear. So far, there have been various theories (e.g., syntrophic model, autogenous model, viral eukaryogenesis model, exomembrane hypothesis), but few explain why. I observed that C-value (the amount of DNA contained within a haploid nucleus) increased by 3.5 orders of magnitude from prokaryote to eukaryotes, which is inconceivably close to the packing ratio of DNA in extant eukaryotes. Thus, it is never convincing to explain eukaryogenesis solely by using accident phagocytosis, symbiosis or parasitism (the influential endosymbiont theory unfortunately took the wrong turning!), but what is important is to explain why genome increased so sharply. This may be mainly related to DNA replication errors or polyploidization, of course not completely ruling out the possible contribution from lateral gene flow or genetic integration between individuals of different species. It is above suspicion that successful packing of DNA (finally into chromosome) was a key step towards eukaryogenesis, of course also accompanied with structural differentiation in cell and development of more subtle and complex cell division, and so on. This paper presents “packing and structurization hypothesis” to explain eukaryogenesis. In addition, from a molecular genetic point of view, sexual reproduction is never a mystery as it is just a process to merge two individual genomes, by which diverse genetic information of the species are dispersed into its individuals. On the other hand, from an ecological point of view, the original motivation of “sex” was accidently coupled with dormancy.

Key words: eukaryogenesis, DNA, chromosome, packing ratio, “packing and structurization hypothesis”, sexual reproduction, accident dormancy hypothesis