Isochore (genetics) - The Thermodynamic Stability Hypothesis

The Thermodynamic Stability Hypothesis

The isochore theory purported that the genome of "warm-blooded" vertebrates (mammals and birds) are mosaics of long isochoric regions of alternating GC-poor and GC-rich composition, as opposed to the genome of "cold-blooded" vertebrates (fishes and amphibians) that were supposed to lack GC-rich isochores. These findings were explained by the thermodynamic stability hypothesis, attributing genomic structure to body temperature. GC-rich isochores were purported to be a form of adaptation to environmental pressures, as an increase in genomic GC-content could protect DNA, RNA, and proteins from degradation by heat.

Despite its attractive simplicity, the thermodynamic stability hypothesis has been repeatedly shown to be in error . Many authors showed the absence of a relationship between temperature and GC-content in vertebrates, while others showed the existence of GC-rich domains in "cold-blooded" vertebrates such as crocodiles, amphibians, and fish.