TEMPLATE MIXING - A METHOD OF ENHANCING DETECTION AND INTERPRETATION OF CODOMINANT RAPD MARKERS

Ten codominant RAPD markers, ranging in size from about 300 to about 1 350 bp, were identified in mapping populations of chickpea (Cicer arie tinum L.) and diploid strawberry (Fragaria vesca L.). A distinguishing feature of all ten markers, and perhaps of codominant RAPD markers in general, was the presence in heterozygous individuals of a non-parent al, heteroduplex band migrating more slowly than either of the respect ive parental bands. This non-parental band could also be generated by mixing parental DNAs before PCR (template mixing). As a means of ident ifying primers likely to detect codominant RAPD markers, parental and mixed-template (parent-parent) PCR-product gel lanes were compared for 20 previously untested RAPD primers (10-base oligomers). Four primers that produced a total of five non-parental, heteroduplex bands in mix ed-template reactions were selected, and then used to detect a total o f five segregating, codominant markers and nine dominant markers in th e respective F-2 mapping population, a codominant marker frequency of 35.7%. When closely migrating fast and slow bands of codominant RAPDs were difficult to differentiate, parent-progeny template mixing was us ed to deliberately generate heteroduplex bands in fast- or slow-band F -2 homozygotes, respectively, allowing confirmation of marker phenotyp e.