Male viable. Male fertile. Homozygous female viable. Female sterile owing to dm¹. In(1)FM4 is the consequence of the approximate reinversion of In(1)dl-49 in In(1)sc⁸+dl-49 and is similar in sequence to In(1)sc⁸ but with the transposition of 3C-4F into 11F. Unless this small transposition has an abnormally large effect on crossing over (e.g., see Dp(2;2)C619) recombination might be expected to be frequent in FM4/+ heterozygotes and especially in FM4/In(1)sc⁸ heterozygotes. In FM4/+ heterozygotes, double crossovers with points of exchange inside or outside the 3C-11F interval produce euploid X chromosomes and those with one point of exchange inside and one outside produce complementary duplications and deficiencies for 3C - 4F. The duplication survives in either sex and exhibits a Confluens phenotype (E.H. Grell in FBrf0066905); the deficiency might survive in the heterozygote as a "Notch Minute" female judging from the survival of the slightly smaller Df(1)w^m258-44. Balancing properties not well determined.