Editing Gene expression programming (section)

===Multiple main programs and multicellular systems===
Multicellular systems are composed of more than one [[gene expression programming#Homeotic genes and the cellular system|homeotic gene]]. Each homeotic gene in this system puts together a different combination of sub-expression trees or ADFs, creating multiple cells or main programs.

For example, the program shown in the figure was created using a cellular system with two cells and three normal genes.

[[File:Expression of a multicellular GEP system with 3 ADFs and 2 main programs.png|thumb|Expression of a multicellular system with three ADFs and two main programs. a) The chromosome composed of three conventional genes and two homeotic genes (shown in bold). b) The ADFs encoded by each conventional gene. c) Two different main programs expressed in two different cells.]]

The applications of these multicellular systems are multiple and varied and, like the [[gene expression programming#Multigenic chromosomes|multigenic systems]], they can be used both in problems with just one output and in problems with multiple outputs.