--Yong-Bao Pan and Peter A. Peterson

Since our first report on C-I-m846079, a highly mutable allele (MNL 61:5), several genetic experiments have been completed. To understand how this mutable allele acts, we crossed this allele with both C (of different sources) and c (of c sh wx tester) alleles. Although a mutable phenotype was always observed for a C/C-I-m846079 genotype, the c/C-I-m846079 only yield a colorless phenotype (data not shown). This observation leads to two conclusions. First, C-I-m846079 does not encode a functional C gene product; secondly, the normal inhibitive function of the C-I-m allele is interrupted by an insertion at the C-I locus unless the insert excises. Therefore, the highly mutable phenotype observed for a C/C-I-m846079 genotype represents many colorless sectors on a colored background, indicating that an excision event at C-I-m yields a normal C-I allele leading to a colorless sector.

The transposable insert of this mutant has also been studied. By crossing to appropriate reporter allele testers, we observed no other families of active transposable elements except Cy elements in this mutant. These tests included Ac, En, Uq, Dt, Mrh, Fcu, Bg (data not shown). In addition, the mutant contains at least 5 independently segregating active Cy elements in its genome (data not shown). Exceptional colorless derivatives of C/C-I-m846079 arise and these are not transactivated by Cy.

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