The distribution of molecules in an embryo is key to the separation and development of its systems. Specialised proteins find their place through a sequence of chemical and physical changes that give the developing embryo orientation.
A morphogen is a chemical gradient which plays a role in the early stages of embryo pattern development (morphogenesis). Unequal distribution of proteins or other factors forms morphogens within a newly fertilised zygote or developing embryo. Establishing these gradients is a key mechanism for defining the axes within the organism around which development may proceed. Anterior-posterior polarity in the nematode worm C. elegans is dictated by the flow of cytoplasmic granules and PAR proteins to one side of the the embryo. Computer modelling can be a useful tool for studying hypotheses surrounding morphogen gradients during the development of the embryo.