The genetics of the diploidized tetraploid Avena barbata

Abstract

Formal genetic studies of six pairs of enzyme loci in Avena barbata, a tetraplold grass with 2n = 4x = 28 chromosomes, are reported. We obtained data from an F₂ self-fertilized progeny of an F₁ hybrid between two California genotypes and from self-fertilized progenies of heterozygous plants collected in nature. The results indicate that the phenotype scored from our gels for each locus pair was the product of four “homoeoalleles,” two carried by one pair and two by the other pair of homoeologous chromosomes of this tetraplold. In each case observed segregations fit expectations for pairs of independently segregating loci with codominant alleles. A. barbata thus behaves genetically as a diploidized tetraplold, i.e., a tetraploid in which pairing is preferential within each pair of homologues rather than at random among the four chromosomes of each homoeologous set. We studied one pair of loci for each of acid phosphatase, esterase, leucine aminopeptidase, and peroxidase and two pairs of loci for 6-phosphogluconate dehydrogenase. One of the acid phosphatase loci is linked to one of the peroxidase loci and both pairs of 6-phosphogluconate dehydrogenase loci are linked to each other and to the pair of leucine amlnopeptidase loci. It also is likely that the second acid phosphatase locus and the second peroxidase locus are linked but this could not be demonstrated because both loci were monomorphic in all of our population samples.