The most common di-nucleotide motif was AT/TA (75%), followed by AG/TC (20%) while AC/TG microsatellites were uncommon.
The AT motif was the most common di-SSR in C. japonica, accounting for 303 (7.6%) of the 4,003 pure SSRs.
The most common di- and tri-nucleotide motifs were AT (9.6%) and AAC (19.0%) (Table 4), in contrast to the observation in a previous study, where AG and AAG were the predominant motifs [ 10, 14, 36- 39].
The motif types (AG n and (AAG n have been reported as the most common di- and tri-nucleotide repeats identified in other plant EST databases [ 43, 45- 47], including peanut (A. hypogaea) [ 15, 30, 37, 40, 48, 49].
In human, Caenorhabditis, and Arabidopsis genomes, the most common di-nucleotide repeats are (AC n, (AG n, and (AT n, respectively, demonstrating that different species have different motif frequency distributions.
AG is the most common di-nt motif in exons and 5'flanking regions, while AT is most common in introns, intergenic regions, 3' flanking regions (Zhang et al., 2004).
The most common di-, tri-, and tetranucleotide motifs are AG/CT (25 32% of SSRs), AAG/CTT (9 19% of SSRs), and TTTC/GAAA (2 4% of SSRs), respectively.
This result agrees with a previous study [ 70] that reported that of the three most common di-nucleotide repeat units in Drosophila melanogaster (TC/AG, AT/TA, and GT/CA), microsatellite loci with repeat units GT/CA and TC/GA had higher mutation rates than loci with repeat unit AT/TA.
Furthermore, SSRs acquired by these methods are limited with probed SSR motifs (most common are di or tri types), and hence the advantages are partially offset.
The evidence on the association of the most common phthalate, di-2-ethylhexyl phthalate (DEHP) with adverse pregnancy outcomes remains equivocal.
