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Fig. 7. Schematic representing the Egfr-mediated signalling events during Ato
expression (green). In wild type, Egfr signalling is occurring in the IGs.
This signalling occurs at the same time as R8 precursor selection within the
equivalence group, and the role of Ed is to prevent the Egfr signalling from
interfering with this process. In ed mutants, there is no Ed protein
and Egfr signalling has a local inductive effect on the cells of the
equivalence group resulting in the selection of more than one R8
precursor.