Animal Genomes Evolve Along Irreversible 'Highways,' Largest-Ever Comparison Finds

An international team led by scientists at the University of Vienna has compared more than 5,800 chromosome-scale animal genomes spanning 4,454 species across 19 animal phyla — the largest such comparison across the animal tree of life to date — and found that animal genomes evolve along a limited set of irreversible 'evolutionary highways,' according to a study published in Science Advances.

Most sequenced genomes are 'drafts' that show which genes an animal has but not how they are arranged. Chromosome-scale assemblies instead place every gene in order along complete chromosomes; they are far harder to produce, and only recently have enough species been sequenced this way to allow a comparison across the whole animal kingdom. The team built a new framework, called evolutionary genome topology, that projects this diversity onto a single map.

At the centre of the pattern is a process the team calls 'fusion-with-mixing': when two chromosomes fuse, their genes intermingle in a way that cannot be undone, leaving a permanent record of the event. The researchers found that differences in chromosome number across animal groups arise either from the combination of ancestral chromosomes or from their separation, and in both cases, fusion-with-mixing sends lineages along distinct evolutionary paths, placing major animal groups in separate regions of what the team calls 'genome architecture space.'

The researchers said some groups — including mosquitoes, glass sponges and earthworms — occupy unique, isolated regions of the map with no close parallel among the other animals studied.