Evolution of linkage and genome expansion in protocells: The origin of chromosomes

Autoři: András Szilágyi aff001;  Viktor Péter Kovács aff001;  Eörs Szathmáry aff001;  Mauro Santos aff001
Působiště autorů: Institute of Evolution, Centre for Ecological Research, Tihany, Hungary aff001;  Department of Plant Systematics, Ecology and Theoretical Biology, Eötvös Loránd University, Budapest, Hungary aff002;  Center for the Conceptual Foundations of Science, Parmenides Foundation, Pullach/Munich, Germany aff003;  Grup de Genòmica, Bioinformàtica i Biologia Evolutiva (GGBE), Departament de Genètica i de Microbiologia, Universitat Autonòma de Barcelona, Bellaterra, Barcelona, Spain aff004
Vyšlo v časopise: Evolution of linkage and genome expansion in protocells: The origin of chromosomes. PLoS Genet 16(10): e32767. doi:10.1371/journal.pgen.1009155
Kategorie: Research Article
doi: 10.1371/journal.pgen.1009155


Chromosomes are likely to have assembled from unlinked genes in early evolution. Genetic linkage reduces the assortment load and intragenomic conflict in reproducing protocell models to the extent that chromosomes can go to fixation even if chromosomes suffer from a replicative disadvantage, relative to unlinked genes, proportional to their length. Here we numerically show that chromosomes spread within protocells even if recurrent deleterious mutations affecting replicating genes (as ribozymes) are considered. Dosage effect selects for optimal genomic composition within protocells that carries over to the genic composition of emerging chromosomes. Lacking an accurate segregation mechanism, protocells continue to benefit from the stochastic corrector principle (group selection of early replicators), but now at the chromosome level. A remarkable feature of this process is the appearance of multigene families (in optimal genic proportions) on chromosomes. An added benefit of chromosome formation is an increase in the selectively maintainable genome size (number of different genes), primarily due to the marked reduction of the assortment load. The establishment of chromosomes is under strong positive selection in protocells harboring unlinked genes. The error threshold of replication is raised to higher genome size by linkage due to the fact that deleterious mutations affecting protocells metabolism (hence fitness) show antagonistic (diminishing return) epistasis. This result strengthens the established benefit conferred by chromosomes on protocells allowing for the fixation of highly specific and efficient enzymes.

Klíčová slova:

Deletion mutation – Evolutionary genetics – Fitness epistasis – Genomics – Chromosome structure and function – Natural selection – Parasite evolution – Ribozymes


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