Coming up in the American Journal of Botany in 1999

Title: Physical mapping of ribosomal RNA genes in peonies (Paeonia) by fluorescent in situ hybridization: implications for phylogeny and concerted evolution.

Authors: Daming Zhang and Tao Sang

Fluorescent in situ hybridization has been used increasingly to determine physical locations of genes on chromosomes. Here we generated physical maps of the 18S-5.8S-26S ribosomal RNA genes (rDNA) for five diploid peony (Paeonia) species. We found that the proportion of chromosomes bearing rDNA sites is rather high in peonies compared to that of other flowering plants. We are not aware of any other report of an angiosperm species with rDNA sites on all chromosomes, as found in Paeonia veitchii and P. emodi. All of the r DNA loci were mapped near the telomers of chromosomes in the peony species. We suggest that chromosomal location of rDNA loci has a more substantial impact on the tempo of concerted evolution than the number of loci.