An allotetraploid species, with two sets of homoeologous gene loci, can lose the function of genes from one of its diploid parents at any given locus without deleterious loss of gene product. This silencing of gene loci can be visualized through enzyme electrophoresis when the gene products of the parental diploid species migrate differentially and one of these contributions is clearly missing in the allotetraploid. Werth and Windham postulated that extensive gene silencing over time could produce evolutionary change in allotetraploids including divergent evolution between genetically isolated lines. Botrychium species present a model for testing the possibility of morphological divergence of allotetraploid lines through differential gene silencing. Botrychium lunaria and B. lanceolatum each display a number of unique allozymes revealing them as the unquestionable parents of the widespread tetraploid B. pinnatum. Recently discovered B. "alaskense" is equally unquestionably a tetraploid product of the same parental diploids, yet it is quite distinct morphologically from B. pinnatum. Allozyme patterns show these taxa to be differentially silenced at 50% of the loci examined in which silencing is detectable.

Key words: Allotetraploid, Botrychium, gene silencing, speciation