Michael J McConnell1,2
, Hugh R MacMillan3
and Jerold Chun2 
1
Crick-Jacobs Center for Theoretical and Computational Biology, Salk Institute for Biological Studies, La Jolla, CA 92037, USA
2
Helen L Dorris Neuropsychiatric Disorder Institute and Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA
3
Department of Mathematical Sciences, Clemson University, Clemson, SC 29634, USA