MOLECULAR MARKERS AS A TOOL FOR ANALYZING GENETIC DIVERSITY AND GENOME EXPRESSION IN MAIZE

Neutral markers, such as isoenzymes and RFLPs (restriction fragment le ngth polymorphism), have applications in various fields of genetics an d breeding. Three examples are documented. Firstly, about 130 maize li nes were compared using 46 RFLP probes distributed over the 10 chromos omes. Data analyses and distance indices gave a classification consist ent with heterotic groups and pedigrees, showing the value of molecula r markers for characterizing unknown material. Distance indices were n ot very useful for predicting heterosis when parental lines belong to different genetic groups: the identification of polymorphisms of genes involved in the traits analysed is required. Second, enzyme markers w ere used to follow introgression of exotic into adapted material, in a n experiment on cold tolerance. The classification observed revealed n either genetic drift nor selection. Finally, using a saturated genetic map constructed from an F2 progeny, we located QTLs (quantitative tra it loci) for agromorphological traits and QTLs for amounts of proteins as revealed by 2-dimensional electrophoresis and quantified with a co mputer-assisted system. The comparison of genetic parameters (dominanc e, epistasis) between these 2 contrasted phenotypic levels suggested t hat interactions are much more common at the gene product level than a t the macroscopic level.