function of each gene product by systematic alteration of its concentration in the cell. Rapid, genome-scale systems to silence gene expression are a desirable goal, as is the capacity to target mutations, insertions, and deletions to specific genomic regions and genes via allele replacement. Those techniques will serve as research tools and enable allele replacement in crop improvement.
Natural variation as a source of functional information. The development of quantitative-trait loci (QTLs) and linkage-disequilibrium analytic tools in the model and reference species is vital for assigning function to genes. High-throughput mutant and allele detection systems are also vital, as are reliable systems to detect single-base mismatches. They require appropriate mapping populations, particularly as related to exploitation of natural variation in crop and noncrop species in which the focus is on the identification of valuable alleles, not only the elucidation of gene functions at particular loci. The study of multitrait quantitative genetics is an important way to assign function to some genes (such as those whose mutations result in lethal phenotypes) and to discover proteins that are rate-limiting for important traits. Plant biology’s historical exploitation of natural variation as the raw material of breeding provides a wealth of extractable information, as does the availability of wild accessions of many species.