Mutations and Chromosomal Rearrangements Affecting the Expression of Snail, a Gene Involved in Embryonic Patterning in DROSOPHILA MELANOGASTER.

Mutants at the snail locus are zygotically acting embryonic lethals that affect dorsoventral patterning. A comparison of seven mutant alleles shows considerable variation in expressivity and a graded effect along the dorsoventral axis: more extreme alleles result in the abnormal development of the dorsally derived ectoderm as well as the ventrally derived mesoderm, whereas weaker alleles affect only development of the mesoderm. Animals transheterozygous for different mutant alleles occasionally survive to adulthood; they frequently have missing halteres and more rarely are hemithorax. The mutant phenotype of snail is shown here to be enhanced zygotically by haploidy of two nearby regions on the second chromosome: the elbow to no-ocelli region and the interval defined by l(2)br36 and l(2)br37. It is concluded that the products of all of these genes function together in the process of specification of pattern in the embryo.