GENOMIC MAP OF A DIPLOID HYBRID SPECIES

Several fertile diploid plant species have been shown to be derived from hybridization between species with strong chromosomal sterility barriers, yet little is known about the genomic processes that accompany this mode of speciation. As a first step toward understanding these processes we have generated a detailed genetic linkage map for Helianthus anomalus, a diploid species derived via hybridization between H. annuus and H. petiolaris. This was generated using 161 RAPD loci and one isozyme locus. The genetic markers were distributed into 18 linkage groups and cover 2338 cM. Analysis of the parental origin of each locus/allele revealed that 44 were originally derived from H. annuus, 37 were derived from H. petiolaris, 54 could have been derived from either parent, and 25 were unique to H. anomalus. In addition, the parental linkage groups were not transmitted or retained intact in the hybrid species. Rather, molecular markers originating from both parental species were interspersed within individual H. anomalus linkage groups. Although there are several limitations to analysing hybrid genomic composition using this approach, these results do raise the possibility that diploid hybrid species may be able to retain different portions and/or proportions of their parental species' genomes. This characteristic may provide diploid hybrid species with greater flexibility than allopolyploid species in terms of optimizing their genomes for a new ecological niche and may permit the production of several different diploid hybrid species from the same two parents, as appears to have happened in Helianthus.