<P> A second model proposes that proto - eukaryotic cells evolved from bacteria without an endosymbiotic stage . This model is based on the existence of modern planctomycetes bacteria that possess a nuclear structure with primitive pores and other compartmentalized membrane structures . A similar proposal states that a eukaryote - like cell, the chronocyte, evolved first and phagocytosed archaea and bacteria to generate the nucleus and the eukaryotic cell . </P> <P> The most controversial model, known as viral eukaryogenesis, posits that the membrane - bound nucleus, along with other eukaryotic features, originated from the infection of a prokaryote by a virus . The suggestion is based on similarities between eukaryotes and viruses such as linear DNA strands, mRNA capping, and tight binding to proteins (analogizing histones to viral envelopes). One version of the proposal suggests that the nucleus evolved in concert with phagocytosis to form an early cellular "predator". Another variant proposes that eukaryotes originated from early archaea infected by poxviruses, on the basis of observed similarity between the DNA polymerases in modern poxviruses and eukaryotes . It has been suggested that the unresolved question of the evolution of sex could be related to the viral eukaryogenesis hypothesis . </P> <P> A more recent proposal, the exomembrane hypothesis, suggests that the nucleus instead originated from a single ancestral cell that evolved a second exterior cell membrane; the interior membrane enclosing the original cell then became the nuclear membrane and evolved increasingly elaborate pore structures for passage of internally synthesized cellular components such as ribosomal subunits . </P>

Who discovered the genetic material in the nucleus of cells