RFLP analysis of complex traits in crop plants

Detailed genetic maps, based upon molecular markers (in particular, on restriction fragment length polymorphisms-RFLPs) have now been constructed for a number of crop plant species, and permit a range of genetic analyses hitherto considered impossible. The availability of such maps has made it possible to approach the dissection and manipulation of both simply-inherited and complex characteristics. Even those characters that show apparently 'quantitative' inheritance (displaying essentially continuous variation within a segregating family) can frequently be resolved into a handful of major gene effects. Once tagged with molecular markers, the genes can be assembled in any desired combination, permitting the testing of hypotheses on gene action/interaction, or the construction of varieties of plant species with improved agronomic performance. The next technological challenge is to 'walk' from RFLP markers to isolate the actual genes responsible for the complex trait, by a combination of genetical and physical mapping techniques. Such analyses will begin to clarify our picture of the relationship between genetic and physical maps, of recombination, and of the arrangement of diverse families of DNA sequences in plant genomes.