An extension of this, particularly amongst mammals but also with chicken, is to identify conserved linkage groups, and this may have particular value in positional cloning projects. Conserved linkage, or conserved synteny, can in fact be used to great advantage in comparative genomics, particularly if a genome is smaller and easier to work with than the human genome. It was Sydney Brenner who realised the need for a simple genome approach to gene identification and characterisation, and he also defined the criteria by which the model should be selected. He reasoned that all vertebrates would have a similar repertoire of genes, due to the way in which genomes have evolved. Thus, a vertebrate with a small genome should be the starting point for investigation.
Vertebrates have a similar early developmental pattern and are physiologically similar.
Sydney Brenner suggested that it was the way in which genes are regulated and rather than different genes that gave rise to vertebrate diversity. For these gastronomic reasons, stocks of fish are farmed yearly and a reliable source of one large species, Fugu rubripes, is always available. Although the coding sequence is the same size, intron sizes are greatly reduced. There were however more important conclusions to be drawn. Finally, and critically, homology between Fugu and mammalian genes is high enough to facilitate easy identification both through hybridisation and database comparison.