FIG 4.

Subdomain presorting and logistic negotiation during chromosome segregation. Red and blue lines designate daughter duplexes containing, correspondingly, “Watson” or “Crick” strands of the parental duplex. (A to D) Prokaryotic chromosome. (A) The theta-replicating chromosome with a single-duplication bubble. (B) A similar replicating chromosome with four duplication bubbles. (C) Progressive segregation from a single-duplication bubble by default yields two completely separate daughter nucleoids. (D) Progressive segregation without subnucleoid presorting yields two daughter nucleoids intertwined due to misclustering of the individual subnucleoids. As a result, the daughter DNA duplex containing, for example, the “Watson” strand of the parental duplex finds itself in both daughter nucleoids. (E to J) Eukaryotic chromosome. (E) Still-to-be-condensed sister chromatids after replication. (F) Gradual condensation sorts sister chromatids out at the level of subdomains. (G) Coordinated condensation results in “single-body” chromosomes ready for segregation. (H) Uncoordinated independent condensation centers produce entangled subdomains. (I) Monocentric chromosomes condensed as “one body” should be able to disentangle during segregation. (J) Holocentric chromosomes likely need logistic negotiation to help sort out all the Watson subdomains (one sister) from all the Crick subdomains (the other sister) before segregation can even take place.