Loss of duplicate gene expression in tetraploid Chenopodium

Abstract

Genetic analyses indicate that single-banded leucine aminopeptidase (LAP) phenotypes in tetraploid Chenopodium reflect homozygosity for null alleles at either locus of a polyduplicated pair. Other duplicated isozyme loci show simplification to the diploid phenotype. Loss of duplicate gene expression in the LAP system has occurred independently in putatively specialized taxa occupying the distributional periphery of a New World tetraploid complex. The geographic/taxonomic pattern of genetic variation suggests that fixation of null alleles is mediated by stochastic genetic phenomena associated with migration. Plants homozygous for null alleles at both LAP loci show no detetable activity in assays involving several exopeptidase substrates, although growth and fertility of double-null plants are not markedly reduced. Our data confirm that loss of duplicate gene expression can occur in isozyme systems of polyploid plant taxa. Thus, lack of electrophoretically detectable duplicate gene expression is not a certain indication of diploidy. However, loss of duplicate gene expression in population systems known to be of allopolyploid origin is a clear indication of phyletic derivation.