# Network Motifs

Consider a real transcription network with $N$ nodes and $E$ edges. Then we can write a computer programm that produces an ensemble of random networks. We can then calculate the probability, as well as the mean value and variation of obtaining a certain network structure (pattern). If we now compare the number of recurring patterns in the real network to the randomised network, some patterns occure much more often than in the random network and are called network motifs. The reason why network motifs occure much more often than at random is, that through evolution this patterns provided an advantage and helped the organism to survive thus they are more abundant than expected at random.