Gene tagging with random amplified polymorphic DNA (RAPD) markers for molecular breeding in plants

Markers are of interest to plant breeders as a source of genetic informatio n on crops and for use in indirect selection of traits to which the markers are linked. In the classic breeding approach, the markers were invariably the visible morphological and other phenotypic characters, and the breeders expended considerable effort and time in refining the crosses as the tight linkage or association of the desired characters with the obvious phenotyp ic characters was never unequivocally established. Furthermore, indirect se lection for a trait using such morphological markers was not practical due to (1) a paucity of suitable markers, (2) the undesirable pleiotropic effec ts of many morphological markers on plant phenotype, and (3) the inability to score multiple morphological mutant traits in a single segregating popul ation. With the advancement in molecular biology, the use of molecular mark ers in plant breeding has become very commonplace and has given rise to "mo lecular breeding". Molecular breeding involves primarily "gene tagging", fo llowed by "marker-assisted selection" of desired genes or genomes. Gene tag ging refers to the identification of existing DNA or the introduction of ne w DNA that can function as a tag or label for the gene of interest. In orde r for the DNA sequences to be conserved as a tag, important prerequisites e xist. This review also summarizes the achievements in gene tagging that hav e been made over the last 7 to 8 years.