much of his research has focused on embryogenesis in the fruit fly "drosophila melanogaster", specifically in the patterning that occurs in the early "drosophila" embryo. most of the gene products used by the embryo at these stages are already present in the unfertilized egg and were produced by maternal transcription during oogenesis. a small number of gene products, however, are supplied by transcription in the embryo itself. he has focused on these "zygotically" active genes because he believes the temporal and spatial pattern of their transcription may provide the triggers controlling the normal sequence of embryonic development. saturation of all the possible mutations on each chromosome by random events to test embryonic lethality was done by eric wieschaus. this body of science eventually was termed the heidelberg screen.