eyes mottled wvC/+ females may be N X/Y male viability reduced X/Y/Y male more viable. Characterized by variable degree of instability manifested by production of gynandromorphs, X/0 males and dominant lethals. An extreme example gave 140 females, 106 gynandromorphs, 181 X/0 males and 868 dominant lethals among 1295 putative ring/rod zygotes. Small ring-shaped duplications are generated infrequently (analysis by Hinton, 1955). Behavior of rod derivatives of In(1)wvC (Hinton, 1957, Genetics 42: 55-65) suggests generation of dicentrics through sister-strand fusion rather than exchange. Fusion postulated to occur in heterochromatin of the 3C1 | 20F reunion point of In(1)wvC. Mitotic abnormalities in cleavage of In(1)wvC embryos described (Hinton, 1959, Genetics 44: 923-31). Chromosome tends to become stable in stocks. Viability and fertility correlated with stability. Widely used in mosaic analysis and fate mapping (e.g., Garcia-Bellido and Merriam, 1969, J. Exp. Zool. 170: 61-76).