Comparing genomes across species reveals which genes are so functionally essential that purifying selection has kept them nearly unchanged for hundreds of millions of years.
conservation(t+1) = conservation(t) - mutationRate*dt + selection*(1-conservation)
- Gene nodes — orthologous gene copies traced across multiple species' genomes.
- Synteny connectivity — how much conserved gene order (synteny) links genomes together across evolutionary distance.
- Mutation rate — background rate of sequence change accumulating in each lineage per generation.
- Purifying selection — how strongly natural selection removes deleterious mutations, keeping essential genes conserved.
Comparative genomics is how biologists identified that humans and chimpanzees share ~98.8% sequence identity, and pinpointed the small set of regulatory (not protein-coding) changes responsible for most phenotypic divergence.