REGIONS OF RELATIVE GC% UNIFORMITY ARE RECOMBINATIONAL ISOLATORS

Abstract

Among species within a phylogenetic group, genomic GC% values can cover a wide range that is particularly evident at third codon positions. However, among genes within a genome, genic GC% values can also cover a wide range that is, again, particularly evident at third codon positions. Individual genes and genomes each have a "homostabilizing propensity" to adopt a relatively uniform GC%. Each gene (a "microisochore") occupies a discrete GC% niche of relatively uniform base composition amongst its fellow genes, which can collectively span a wide GC% range. Homostabilization serves to recombinationally isolate both genome sectors (facilitating gene duplication and differentiation) and genomes (facilitating genome duplication and differentiation; e.g., speciation). Although they may sometimes be in conflict, the individualities of genomes, and of genes within those genomes, are separately sustained by a common mechanism, uniformity of GC%. The protection against inadvertent recombination afforded by GC% differentiation is, in the general case, a prerequisite for phenotypic differentiation.