The Drosophila larva shows a clear segmental patterning. The subdivision of the fly embryo into segmental entities is a stepwise process that takes place within the first three hours of development.

To understand the genetic program that leads to the segmental subdivision of the body, Christiane Nüsslein-Vollhard and Eric Wieschaus carried out a large screen for mutants in which the patterning process is impaired. The analysis of the mutants identified was the first step towards a detailed understanding of the underlying genetic program that leads to the formation of the larval metameric pattern.

The Drosophila larva bears characteristic rows of denticles at its ventral side. Segments in different parts of the body show characteristic denticle patterning, and within each segment, single cell rows can be identified through absence or presence, as well as characteristic shape of the denticles. Nüsslein-Vollhard and Wieschaus interpreted mutant phenotypes by analyzing these denticle patterns.