Plant Genome IV Conference Plant Genome IV Conference
Comparative mapping has provided evidence for impressive levels of molecular marker/linkage conservation among species. Within the grass family, for example, we now appreciate that the genetic similarities are greater than ever expected. Consideration of the comparative mapping results leads to applications of the concept to may other situations. (1) Many plant species have little or no genetic mapping information available often because of complexities in their biological life cycle or reproductive biology. The demonstration of similar linkage relationships in even a few initial tests significantly increases the options available for genetic analysis of that species. (2) The existence of such a high degree of linkage similarities implies that traits of similar nature, even if given different names, may have the same or similar flanking sequences. Thus genes isolated in one species become more likely candidate genes in another species if flanked by the same sequences. (3) Quantitative trait loci for a specific trait may be determined to be on many different chromosomes. The comparative mapping concept leads to the idea that some of these loci arose from one founder locus. If that locus became multiplied throughout the genome, is it possible that probes detecting a multilocus sequence where one is linked to one of the QTLs also would detect sequences linked to some of the other QTLs? (4) Although RFLP mapping increased awareness of the presence of duplicate loci, comparative mapping in maize, for example, amplified this information to the point that an ancient tetraploid origin of maize is thought to be highly probable. Possible interactions between these "subgenomes" can now be studied in a much more systematic manner. (5) Plants have recently been generated with the normal number of oat chromosomes plus on chromosome pair of maize. Such strains provide advantages for mapping multilocus sequences in maize even when monomorphic. Comparative mapping considerations guide the kinds of experiments undertaken. A cautionary note should be made, however, because repetitive sequences do not show such species conservation. Examples such as the above will be reviewed in an attempt to illustrate the importance of the exciting information deriving from comparative mapping studies.