In the early studies of Drosophila, mutations
were merely used as "markers" to study the arrangement of genes
on chromosomes. The use of mutants to study Drosophila development,
as we understand it today was pioneered by Don Poulson. In 1940, he studied
the effect of X-chromosomal deletions on embryonic development, and found
that lack of Notch results in neural hyperplasia.
Other attempts to understand development by studying mutants followed.
The use of genetic mosaics to study "non-autonomy" has its origin
in experiments from Alfred H. Sturtevant around 1930, but was rediscovered
by Curt Stern in 1968, who used the method to study bristle pattern. He
discovered that some genes were affecting a "prepattern", while
others were required to respond to this prepattern. Antonio Garcia-Bellido
used genetic mosaics to address a different question. He was interested
in "lineage analysis", mapping the origin of adult structures
to the embryo. The concept of "selector genes" defining compartments
was formulated in 1973.
The bithorax mutant, initially identified by Calvin B. Bridges
in 1915, was picked up in 1946 by Ed B. Lewis. Again, his initial interest
was to understand the chromosome structure of the bithorax complex.
In the 1950s and 60s, Lewis discovered a correlation between the chromosomal
arrangement of genes in the bithorax complex and the order of segments
they affect in the fly. He proposed that each gene in the linear array
functions to give a more posterior identity to the segment in which it
In 1980, Christiane Nüsslein-Volhard and Eric Wieschaus published
the results of a systematic saturation screen for mutations that affect
the early patterning of the embryo. The analyses of the mutants lead to
a deep insight into early development. The relevant genes were grouped
into classes, which act sequentially to subdivide of the embryo into segments.
Four years later, the contribution of the mother for early embryonic development
was included. The screen was momentous in many ways. First, it turned
the attention of the field to embryonic development. Genetic understanding
of developmental biology had so far mainly focused on the analysis of
adult phenotypes. And second, with the rising field of molecular biology,
the genes were characterized and embryonic patterning understood at the