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Molecular cytogenetic analysis of recently evolved Tragopogon (Asteraceae) allopolyploids reveal a karyotype that is additive of the diploid progenitors¹

²Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK; ³School of Biological Sciences, Queen Mary College, University of London, E1 4NS, UK; ⁴Institute of Biophysics, Academy of Sciences of the Czech Republic, Kralovopolska 135, CS-61265 Brno, Czech Republic; ⁵Florida Museum of Natural History and the Genetics Institute, University of Florida, Gainesville, Florida 32611 USA; ⁶Department of Botany and the Genetics Institute, University of Florida, Gainesville, Florida 32611 USA

Tragopogon mirus and T. miscellus (both 2n = 4x = 24) are recent allotetraploids derived from T. dubius x T. porrifolius and T. dubius x T. pratensis (each 2n = 2x = 12), respectively. The genome sizes of T. mirus are additive of those of its diploid parents, but at least some populations of T. miscellus have undergone genome downsizing. To survey for genomic rearrangements in the allopolyploids, four repetitive sequences were physically mapped. TPRMBO (unit size 160 base pairs [bp]) and TGP7 (532 bp) are tandemly organized satellite sequences isolated from T. pratensis and T. porrifolius, respectively. Fluorescent in situ hybridization to the diploids showed that TPRMBO is a predominantly centromeric repeat on all 12 chromosomes, while TGP7 is a subtelomeric sequence on most chromosome arms. The distribution of tandem repetitive DNA loci (TPRMBO, TGP7, 18S-5.8S-26S rDNA, and 5S rDNA) gave unique molecular karyotypes for the three diploid species, permitting the identification of the parental chromosomes in the polyploids. The location and number of these loci were inherited without apparent changes in the allotetraploids. There was no evidence for major genomic rearrangements in Tragopogon allopolyploids that have arisen multiple times in North America within the last 80 yr.

Key Words: centromere • chromosomal evolution • fluorescent in situ hybridization (FISH) • genome size • polyploidy • rDNA • subtelomere • Tragopogon

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