CHROMOSOMAL MAPPING OF THE MADS-BOX MULTIGENE FAMILY IN ZEA-MAYS REVEALS DISPERSED DISTRIBUTION OF ALLELIC GENES AS WELL AS TRANSPOSED COPIES

A linker PCR procedure has been developed for preparing repetitive DNA -free probes from genomic clones, which is especially efficient for me mbers of gene families. Using this procedure as well as standard metho ds to prepare hybridization probes, chromosomal map positions of MADS- box genes were determined in recombinant inbred lines of maize (Zea ma ys ssp, mays), It appears that MADS-box genes are scattered throughout the maize genome, While there is evidence that this genomic distribut ion is representative for plant MADS-box genes in general, the followi ng two other observations probably reflect Zea genome organization. Fi rst, at least one family of MADS-box-carrying elements contains line-s pecific versions, which are present in some maize lines at certain chr omosomal positions, but are absent from these loci in other lines. The members of this family resemble transposable elements in some respect s, Secondly, the finding of pairs of highly related MADS-box genes whi ch are accompanied by other duplicated markers is a further indication of the ancestral polyploid genome constitution revealed with other ma rkers, The importance of these findings for an understanding of the ge nomic organization of MADS-box genes and the evolution of the MADS-box gene family is discussed.