Microsatellite loci are not conserved across the Asteraceae.

Microsatellite loci (also known as simple sequence repeats [SSRs] or simple tandem repeats [STRs]) are regions of DNA that contain short (<6 bp) tandemly repeated sequences (Litt and Luty 1989; Edwards et al. 199 1; Jacob et al. 199 1). Much attention is currently being paid to the development of microsatellite loci because they display a number of properties of interest for genomic mapping, population genetic, and evolutionary studies (Terauchi and Konuma 1994). They occur in large numbers within the genome: Edwards et al. (1991) estimated that 400,000 trior tetrameric repeats with more than seven repeated units occur in the human genome. Condit and Hubbell (1991) estimated the frequency of poly(AC) and poly(AG) repeats in six species of higher plants at between 5 X lo3 and 3 X 105. Similar numbers have been reported for wheat (Roder et al. 1995). Microsatellite loci are generally highly polymorphic, with large numbers of low-frequency alleles that are codominantly expressed (Akkaya, Bhagwat, and Cregan 1992; Hughes and Queller 1993; Saghai Maroof et al. 1994; Chase, Kesseli, and Bawa 1996). For example, Terauchi and Konuma (1994) found an average of 6.2 alleles per locus in a survey of 23 individuals of wild yam (Dioscorea tokoro), whereas allozyme surveys of 1,128 individuals revealed only 2.5 alleles per locus (Terauchi 1990). In spite of these properties, primers for microsatellite loci are presently available for a limited number of taxa. However, surveys of primer conservation in a number of animal groups have revealed that primers developed for one taxon can often amplify homologous microsatellite loci in related taxa, and sometimes in widely divergent taxa (Moore et al. 1991; Schlotterer, Amos, and Tautz 199 1; Stallings et al. 1991; FitzSimmons, Moritz, and Moore 1995). In the most striking example, primers developed from nucleotide sequences from one family of marine turtles (Cheloniidae) amplified homologous loci in other marine and terrestrial turtles, representing a divergence time of approximately 300 Myr (FitzSimmons, Moritz, and Moore 1995). The degree of conservation of microsatellite loci across plant taxa has not been explicitly addressed in a broad taxonomic group. Zhao and Kochert (1993) found that primers for a (GGC), microsatellite locus developed for rice amplified a homologous locus in maize and bamboo. Lagercrantz, Ellegren, and Andersson (1993) attempted to amplify five microsatellite loci in four species of Brassica using primers developed from B. napus