Anderson and Kohn, page 1 Dikaryons, diploids, and evolution

The regular association of unfused, haploid, gametic-type nuclei within the dikaryon is a striking outcome of evolution that is unique to the fungi. Many fungi with normally dikaryotic mycelia can also exist as diploids (12, 32, 44, 55, 59). What are the genetic and evolutionary implications of dikaryosis and diploidy? Remarkably, the majority of the genetic inferences about dikaryons, diploids, and their interactions reviewed by John Raper in Genetics of Sexuality in Higher Fungi in 1966 (66) remain essentially unchanged to the present. While the genetics of dikaryons and diploids have been established for more than 40 years, the evolutionary implications are only now becoming accessible through experiments. The purpose of this review is to examine the immediate and long-term consequences of dikaryosis, with comparison to diploidy. In keeping with the theme of Raper's book, this review focuses on fungi with prolonged dikaryotic phases, mainly the Hymenomycetes (nomenclature of higher taxa follows the Tree of Life Project