To understand neural development different experimental approaches are done in different model system. The distinction between inherited genetic code (genotype) and the corresponding organism (phenotype) is the cornerstone of biology. Genotype is the one that is inherited from the parents. The complete individual that is formed according to the instructions specified in the genotype is the phenotype. One of the model is the simple genetic encoding, direct genotype-phenotype mapping. Deciding on how to encode the network in the genotype that suitable for the application of the genetic operators is important to evolve neural networks. To be able for an individual at the level of the genotype assumes the form of a string of identical elements; phenotypical characteristics are coded in a uniform manner. The transformation of the genotype into the phenotypical network is called genotype-to-phenotype mapping. (Canglenosi, Nolfi, Parisi). One to one mapping has several drawbacks one of them is scalability. The space to be searched evolutionary process increases exponentially with the size of the network (Kitano, 1990), because of the length of the genotype is proportional to the complexity of the corresponding phenotype.
Another method using the genotype and the phenotype is the growing method. The genotype-to-phenotype process in nature is not only an abstract mapping of information from genotype to phenotype but it is also a process of physical growth (growth in size and in physical structure).( Canglenosi, Nolfi, Parisi).
By executing the inherited growing instruction the phenotype is progressively built. Below is the illustration of the development of an evolved neural network. The upper part is the growing and branching process of the axons. The lower part of the illustration is the resulting network after removal of nonconnecting branches and the elimination of isolated neurons and groups of interconnected neurons.
Cellular Encodings - In natural organisms folding in of the ectodermic tissue which forms the neural crest is the beginning of the development of the nervous system. This gives rise to the mature nervous system in succession of three phases: the genesis and proliferation of different classes of neurons by cellular duplication and differentiation, the migration of neurons toward their final destination, and the growth of neuritis (axons,dendrites). Several experimental approaches in modelling neural development are increasing. The above models are study focused by the paper written by Cangolosi, Nolfi, Parisi. Above models are only some of the studies done by several researchers.
Cangelosi, Nolfi, Parisi, Artificial Life Models of Neural Development
Kitano H. (1990). Designing neural networks using genetic