Genome mapping is used to identify the genetic location of mutants, or qualitative and quantitative trait loci (QTL). Linking the traits to markers using genetic and family information of a recombinant population can identify the gene location. Through mapping, we can answer how many loci are involved, where the loci are positioned in the genome, and what contribution each allele may have to the trait. To determine relationships between marker loci and the target trait, mapping requires the following: 0 segregating populations (genetic stocks), 0 marker data set(s), and 0 a phenotypic data set.
The crucial requirement for the success of genome mapping in plant science is the choice of a suitable segregating population. Doubled haploids (DH), recombinant inbred lines (RI), backcrosses (BC), and F, populations are the primary types commonly used for plant genome mapping. Each of these populations has unique strengths and weaknesses. In plant science, the populations are developed from biparental crosses or backcrosses between parents that are genetically different. The resulting F, population is developed by selfing the F, individual. The BC can be developed further by crossing the F, with one of the two parents used in the initial cross.The DH population is usually derived by doubling chromosomes of haploid cells obtained from the F, generation. Various methods have been used to produce doubled haploids in plants, such as ovary culture, anther culture, microspore culture, or chromosome elimination.The RI populations are produced by random selfing or sib-mating of individuals of the F, or BC, population until they become virtually homozygous lines
. Most RI populations have been developed by a single-seed descent method. The population type and the number of progenies determine the resolution of the linkage map.The map in turn affects the precision and accuracy of the number, location, and effect of gene/QTLs (quantitative trait loci), which can be detected. Because of their high heterozygosity,F2and backcross populations, though easy to develop, cannot indefinitely supply resources for DNA studies and multiple replicated experiments are not possible.
The advantage of F2populations over other population types is the large amount of genetic information per progeny, when codominant markers are used. The D H and RI populations, on the other hand, are renewable and more permanent resources, multiple-replicated experiments for QTL analysis are feasible. Because RI populations have undergone additional cycles of recombination during selfing, while F,-derived DH populations have undergone meiosis only once, RI populations are expected to support the generation of higher resolution maps than the DH populations.The DH, RI, and backcross populations, however provide half of the genetic information per progeny as compared to the F2populations
