Construction of a detailed pea genetic linkage map using recombinant inbred lines
Olaszek, Jay C.
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The use of recombinant inbred lines (RILs) in the construction of a detailed genetic linkage map presents several advantages to the mapping investigator. First, as loci are driven to homozygosity by the process of inbreeding, various short linkage blocks become fixed such that additional generations no longer segregate; thus, a perpetual supply of germ plasm is produced. Also, additional meioses throughout the course of inbreeding allow for increased opportunities for recombination, thereby allowing a more accurate estimation of linkage relationships. In this study, a detailed pea genetic linkage map was constructed using recombinant inbred lines. Numerous marker types were employed. Initial efforts focused upon morphological and allozyme characters, with the majority of the emphasis placed upon Random Amplified Polymorphic DNAs (RAPDs). The purpose of such efforts was to confirm the location of numerous markers on a pea genetic linkage map previously constructed using an F2 progeny array and to further refine the map with additional unique markers. Results did in fact confirm the location of almost all markers common to both the F2 and RIL studies. The RIL map is presented in nine linkage blocks corresponding to the seven linkage groups of pea, compared to eight linkage blocks in the F2 study. The initial stages of the study focused on the confirmation of the location of morphological and allozyme loci; later efforts emphasized RAPDs. Mapping efforts involved eleven morphological and six isozyme loci. To complement these, 88 RAPD primers were selected from an original survey of over 400 primers. This resulted in the assignment of 181 markers to the current RIL map, 93 of which are common to the F2 study. Eightyeight additional unique markers were added to the RIL map as well, thereby saturating it further and serving to resolve questionable linkage relationships unanswered by the F2 study. Comparisons of only those markers common to both the F2 and RIL studies did indicate some expansion of RILs over F2S; however, elimination of linkage-phase complications and marker dominance through the use of RILs has resulted in a more detailed map whose linkage relationships are arguably more reliable.