Application of the Near‐Isogenic Line Gene Mapping Technique to Isozyme Markers

Abstract

Near‐isogenic lines (NILs) have been proposed as a genetic resource that can be used to identify linkages between molecular and conventional markers. If the donor parent (DP) and the recurrent parent (RP) possess an allelic contrast for the molecular marker, and if the DP allele is still present in the NIL, then presumptive evidence of linkage between that molecular marker and the intro‐gressed gene can be inferred. The objective of this study was to evaluate this NIL gene‐mapping technique using isozyme markers and a collection of 63 soybean [Glycine max (L.) Merr.] NILs. The electrophoretic isozyme banding patterns of eight enzymes (12 loci) were examined in 35 ‘Clark’ and 28 ‘Harosoy’ RP/NIL/DP trio sets, where each NIL possessed an introgressed conventional gene. Of the 756 combinations of 12 isozyme loci and 63 trio sets evaluated, 256 exhibited RP/DP isozyme allelic differences. Of these 256, seven (four in Harosoy, three in Clark, total of five conventional markers) exhibited an RP/NIL contrast and a corresponding NIL/ DP equality for an isozyme allele. The five different presumptive linkages were: Enp – In, Mpi – dt2, Aco4 – dt2, Mpi – ln, and Pgi – d2. The F2 cosegregation data confirmed the presumed linkages of Enp with ln (9.38 ± 1.55%) and Mpi with dt2 (16.07 ± 6.43%), but refuted the presumed linkages of Aco4 – dt2 and Mpi – ln. The Enp locus is therefore part of Linkage Group 4, which is currently comprised of the v1, ln, and P2 loci. Neither Mpi nor dt2 have been assigned to an existing linkage group, and thus represent a new linkage group. The presumed linkage of Pgi with d2 was not tested, but other data indicated that this presumption was probably erroneous. The confirmation of two of the five presumptive linkages was consistent with the numbers expected based on a previously published theoretical analysis of the NIL gene‐mapping technique.

Dt2Is a Gain-of-Function MADS-Domain Factor Gene That Specifies Semideterminacy in Soybean

“…A previous linkage analysis with 20 F 2 plants demonstrated that Dt2 was linked at ;17% recombination units from the gene MPI (Muehlbauer et al, 1989), which is located at 61.7 Mb, a position that is only ;0.6 Mb from the distal end of the short arm of chromosome 18 (Schmutz et al, 2010). Given this information, we then randomly selected simple sequence repeat (SSR) markers (Song et al, 2010) distributed in the 4 Mb (58 to 62 Mb) genomic segment located at the end of chromosome 18 to genotype the 679 F 2 individuals and mapped the Dt2 locus to a 1.5-centimorgan region between SSR_18_1791 and SSR_18_1842, which spans 263 kb, according to the reference genome sequence ( Figure 1B).…”

“…The Dt1 locus is located on chromosome 19 Tian et al, 2010). The Dt2 locus was inferentially localized to the distal end of chromosome 18 because of its linkage to a gene governing the isozyme mannose-6-phosphate isomerase (MPI) that was mapped there (Muehlbauer et al, 1989).…”

Artificial selection for determinate growth habit in soybean

“…However, in dt1/dt1 genetic backgrounds, the phenotype is determinate, because dt1 is epistatic to Dt2 and dt2 (6). The Dt2 locus was mapped to classical LG #6 (12) and from there to LG G (13). A third allele at the Dt1 locus (dt1-t) has been identified that produces a phenotype that shares some characteristics of both dt1 and Dt2 (14).…”

An Integrative Approach to Genomic Introgression Mapping

“…Historically, the mapping of NIL introgression sites has relied on a wide range of electrophoresis-based molecular tools, including isozyme, RFLP, amplified fragment length polymorphism, and simple sequence repeat (SSR) analyses (Muehlbauer et al, 1989(Muehlbauer et al, , 1991Molnar et al, 2003;Nichols et al, 2006). More recently, automated genotyping technologies have accelerated the efficiency of genetic mapping.…”