Monday, September 8, 2014

Inbreeding creates the most complex networks

In an earlier blog post (The ultimate phylogenetic network?) I reproduced the lattice network from the anthropologist Franz Weidenreich. This comes close to being as complex as a network can get when applied to groups of organisms. However, when we study the genealogy of individuals, the network can get much more complex. This will be most true when there are marriages between close relatives (consanguinity), which creates inbreeding.

The family pedigree (or family tree!) shown here is for a group of people in a recently isolated population from the southwestern area of The Netherlands. There are 4,645 people involved, covering 18 generations (one row each). The average number of consanguineous loops for the 103 study individuals is 71.7, which is what is creating all of the cross-connections that make the network look so horrendous. (Consanguineous or inbreeding loops are illustrated here.)

The genealogy is from:
Liu F, Arias-Vásquez A, Sleegers K, Aulchenko YS, Kayser M, Sanchez-Juan P, Feng BJ, Bertoli-Avella AM, van Swieten J, Axenovich TI, Heutink P, van Broeckhoven C, Oostra BA, van Duijn CM (2007) A genomewide screen for late-onset Alzheimer disease in a genetically isolated Dutch population. American Journal of Human Genetics 81: 17-31.

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