[1] Univ Oxford, Radcliffe Observ Quarter, Math Inst, Wolfson Ctr Math Biol, Woodstock Rd, Oxford OX2 6GG, England
[2] Univ Edinburgh, Western Gen Hosp, MRC Human Genet Unit, MRC IGMM, Edinburgh EH4 2XU, Midlothian, Scotland
[3] Univ Lancaster, Fac Hlth & Med, Div Biomed & Life Sci, Furness Bldg, Lancaster LA1 4YG, England
[4] Univ Bath, Ctr Math Biol, Dept Math Sci, Bath BA2 7AY, Avon, England