Insertion of a 650bp internally deleted P-element (all base pairs between 204 and 2500 are deleted). This P-element is inserted adjacent to the P{KP} element present in the progenitor (sn^BL6) in the 5' non-coding exon of sn, at base pairs 2647 to 2654. The two P-elements are inserted in a tail-to-tail orientation.

Insertion of 0.65kb DNA, very close to the P-element present in the progenitor (sn^BL6). The restriction map of the 0.65kb fragment is consistent with it being part of a P-element.

Unstable allele; can revert to a strong sn phenotype in germ cells. Appreciable somatic reversion of this allele, generating mosaics having patches with a strong sn phenotype, is also seen. The movements of the P-elements in these somatic reversions occur early in development, and require a trans-acting maternal effect component (P\T^Mo). Somatic reversion occurs preferentially in attached-X stocks.

The majority of germline revertants of sn^vw show either a strong sn phenotype or are wild-type. Revertants with a strong sn phenotype appear to result from precise excision of the smaller of the two P-element insertions present in sn^vw. Wild-type revertants appear to result from precise excision of the larger of the two P-element insertions present in sn^vw. Somatic reversion of sn^vw (in males derived from mothers carrying P\T^Mo) is caused by excision of the smaller of the two P-element insertions present in sn^vw.

The rate of somatic reversion (mosaicism) in sn^vw flies derived from females carrying P\T^Mo has been studied. The rate of somatic reversion is reduced threefold if the mother also carries sn^vw.