A composite map of expressed sequences in maize

A maize genetic map based mainly on expressed sequences has been constructed. The map incorporates data from four segregating populations. Three recombinant inbred line populations were derived from the nonreciprocal crosses between three inbred lines. A map derived from an independent F2 progeny from one of the crosses was also used. With a total of 521 genotyped individuals, accuracy in gene order is expected. Five sources of markers were used: (i) 109 loci corresponding to 69 genes of known function, (ii) 39 loci controlling protein position shifts revealed by two-dimensional electrophoresis, (iii) 8 isozyme loci, (iv) 17 loci corresponding to 14 sequenced cDNAs for which no homology was found in gene banks, and (v) 102 loci corresponding to 81 anonymous probes. As many loci were common to all maps, we tested heterogeneity between recombination fractions. The comparison of recombination fractions revealed: (i) a good correspondence between the maps derived from the same cross, (ii) few significant differences in interval distances, and (iii) global differences, which can reach 20% of the total map length. A composite map of 275 loci covering 1765 cM has been constructed. Key words : Zea mays L., RFLP, genetic map, molecular markers, proteins.