Abstract
The properties of three dominant alleles of ftz are described. These alleles cause transformations of the first abdominal segment to the third and cause alternate segment pattern deletions that are out of phase with respect to those caused by ftz null alleles. To explain the effects of these mutations, a model is proposed in which ftz+ has two roles: to subdivide the body into parasegments and to activate appropriate bithorax complex functions in alternate parasegments. According to this model, the effects of the novel ftz alleles can be understood as arising from a slight widening of the blastoderm stripes of ftz expression.
