A chromosome replication pattern deduced from pericarp phenotypes resulting from movements of the transposable element, modulator, in maize.
Modulator (Mp) was mapped after it transposed from the P locus on chromosome 1 by studying 105 light variegated/red twin sectors on medium variegated pericarp ears. Sixty-one percent of the receptor sites were detectably linked to P, and these showed an asymmetry of distribution adjacent to P. No transpositions were mapped in the 4 map units proximal to P, whereas 23 cases mapped to the same length distal to P. The remaining transpositions of Mp on chromosome 1, both proximal and distal to P, were equally scattered. It has previously been shown that when Modulator transposes it replicates at the P locus and a second time at the receptor site. The pattern of transposition adjacent to P is consistent with a hypothesis that a replicon initiation site is situated proximal to P; that Modulator transposes at the time of replication; that it is not able to transpose into a replicated region but only into a replicating one. No difference in distribution of receptor sites was found when the Modulator was detected vs. not detected in the red co-twins by testing with a Dissociation element.
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Genetics and Cell Biology Section, Biological Sciences Group, The University of Connecticut, Storrs, Connecticut 06268.