ABSTRACT The genetic properties of a pleiotropic mutant mapping at 1.4 ± 0.1 in band 3B3 or its adjacent interbands on the X chromosome are described. The mutation is expressed autonomously in germ line cells, where it is recessive and has antimorphic properties. At 29°, the mutation blocks oocyte differentiation, causing female sterility. At lower temperatures, it disturbs the maternal information in the egg; as a result, the progeny lack germ line cells (grandchildless phenotype) and exhibit defects of the cuticular pattern. The mutation is also expressed in somatic cells through zygotic interactions with neighboring regions, including 3A2, 3A3 (zeste), 3C1-2, 3C4 and 3C6-8 (Notch). We interpret the data by postulating that the expression of sets of dispersed genes might be controlled by the local topology of the chromosome, itself constrained by pairing of dispersed repeated elements. We call the mutation paralog.