Three genes involved in the oxidative burst are closely linked in the genome of the snail, Biomphalaria glabrata

► Allelic variation at SOD1 associates with resistance of a snail to infection by schistosomes. ► Oxidative stress from SOD1 could cause a cost of resistance. ► It is shown that SOD1 is in strong linkage disequilibrium with two antioxidant genes. ► All three genes are also very closely linked (<2 cM). ► We hypothesize the existence of a cluster of interacting genes related to defence.