AUTOPOLYPLOIDY IN TOLMIEA MENZIESII (SAXIFRAGACEAE): GENETIC INSIGHTS FROM ENZYME ELECTROPHORESIS'

Despite over 30 years of speculation, the genetic consequences of autopolyploid speciation are largely unknown. Evidence from several sources indicates that Tolmiea menziesii is one of the best documented examples of autopolyploidy in natural populations. As such, Tolmiea can serve as a model for providing insights into autopolyploid speciation. Data from enzyme electrophoresis indicate that tetrasomic inheritance operates in tetraploid Tolmiea. These data indicate that a chromosome can pair with any of its three homologous chromosomes. For all polymorphic loci, heterozygosity is substantially higher in tetraploid Tolmiea compared to the diploid cytotype. Furthermore, individual tetraploid plants can maintain as many as three or four alleles at a single locus. Enzyme multiplicity was also observed in tetraploid Tolmiea. For the dimeric enzyme PGI, individual tetraploid plants were identified at Pgi-2 that maintained three alleles, resulting in the production of six different enzymes. Although these genetic consequences of autopolyploidy had been predicted, they have not been previously demonstrated for an autotetraploid in nature. The increased heterozygosity and enzyme multiplicity observed may afford an autopolyploid greater genetic and biochemical versatility relative to its diploid progenitor. These findings suggest that tetrasomic inheritance provides a genetic avenue through which autopolyploid speciation can successfully occur.

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