ABSTRACT
Polyploidy has been important for providing spare copies of genes which can evolve new functions. Comparisons of whole genomes provides evidence of complete genome duplication (tetraploidization) in Saccharomyces yeasts and also of doublings early in the development of multicellular animals and again in early tetrapods. There are also numerous duplications of small chromosome segments. Usually, one of the two copies of each duplicated gene either mutates and is lost, or rapidly diverges and acquires a new function.
