Families of clustered microsatellites in a conifer genome

Microsatellite clustering may account for genetic maps which do not coalesc e into the expected number of linkage groups. Microsatellite organization w ithin the large genome of Pinus taeda (1C=20,000 Mb) was determined by (1) testing whether repeat motifs were sequestered within the low-copy DNA kine tic component and (2) testing for repeat motif clusters within DNA fragment s regardless of copy number. Within the low-copy kinetic component, either (AC), or (AG) repeat units were present in 32% of sequences. No repeat moti fs were found in the total genome control. Clustered repeat motifs were fre quent; the (ATG)(n) triplet repeat motif was located upstream from a CG-ric h trinucleotide microsatellite in 26 out of 44 in microsatellite sequences. Fourteen of the clustered (ATG)n sequences could be assembled into four in icrosatellite sequence families based on similarities in the flanking regio ns. Consistent with the DNA turnover model, family members shared similar f lanking regions but differed in repeat motif composition and length.