INTERCHROMOSOMAL RECOMBINATION IN ZEA-MAYS

A new allele of the 27-kD zein locus in maize has been generated by in terchromosomal recombination between chromosomes of two different inbr ed lines. A continuous patch of at least 11,817 bp of inbred W64A, con taining the previously characterized Ra allele of the 27-kD zein gene, has been inserted into the genome of A188 by a single crossover. Whil e both junction sequences are conserved, sequences of the two homologs between these junctions differ considerably. W64A contains the 7313-b p-long retrotransposon, Zeon-1. A188 contains a second copy of the 27- kD zein gene and a 2-kb repetitive element. Therefore, recombination r esults in a 7.3-kb insertion and a 14-kb deletion compared to the orig inal S+A188 allele. If nonpairing sequences are looped out, 20fj singl e base changes, frequently clustered, are present. The structure of th is allele may explain how a recently discovered example of somatic rec ombination occurred in an A188/W64A hybrid. This would indicate that d espite these sequence differences, pairing between these alleles could occur early during plant development. Therefore, such a somatically d erived chimeric chromosome can also be heritable and give rise to new alleles.