The degree distribution of the generalized duplication model

  • Authors:
  • G. Bebek;P. Berenbrink;C. Cooper;T. Friedetzky;J. Nadeau;S. C. Sahinalp

  • Affiliations:
  • Department of EECS, CWRU;School of Computing Science, SFU, Burnaby, BC, Canada;Department of Computer Science, King's College, London, UK;Department of Computer Science, University of Durham, UK;Department of Genetics, CWRU;School of Computing Science, SFU, Burnaby, BC, Canada

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2006

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Abstract

We study and generalize the duplication model of Pastor-Satorras et al. [Evolving protein interaction networks through gene duplication, J. Theor. Biol. 222 (2003) 199-210]. This model generates a graph by iteratively "duplicating" a randomly chosen node as follows: we start at t0 with a fixed graph G(t0) of size t0. At each step t t0 a new node vt is added. The node vt selects an existing node u from V(G(t - 1)) = {v1,...,vt-1} uniformly at random (uar). The node vt then connects to each neighbor of the node u in G(t - 1) independently with probability p. Additionally, vt connects uar to every node of V(G(t - 1)) independently with probability r/t, and parallel edges are merged. Unlike other copy-based models, the degree of the node vt in this model is not fixed in advance; rather it depends strongly on the degree of the original node u it selected. Our main contributions are as follows: we show that (1) the duplication model of Pastor-Satorras et al. does not generate a truncated power-law degree distribution as stated in Pastor-Satorras et al. [Evolving protein interaction networks through gene duplication, J. Theor. Biol. 222 (2003) 199-210]. (2) The special case where r = 0 does not give a power-law degree distribution as stated in Chung et al. [Duplication models for biological networks, J. Comput. Biol. 10 (2003) 677-687]. (3) We generalize the Pastor-Satorras et al. duplication process to ensure (if required) that the minimum degree of all vertices is positive. We prove that this generalized model has a power-law degree distribution.