diff --git a/src/js/ibcJS.js b/src/js/ibcJS.js
index 80321e2341c459042c0f665e85e2857a5c98d99e..95129e4b9c0de365a85edd8a3b61effd23334238 100644
--- a/src/js/ibcJS.js
+++ b/src/js/ibcJS.js
@@ -1,7 +1,7 @@
 window.ibc = (() => {
     // These IDs are considered to be unknown parents
-    let null_ids = [0, -2, -4, -5, -6, -7, -9];
-    let or_null = (s) => (null_ids.contains(s)) ? null : s;
+    let or_null = (s) => specificCharacterID(s) ? s : null;
+    let find_gp = (id) => (slaveStateById(id) || genePool.find((s) => s.ID == id) || null);
 
     // Create a node for the given ID
     let create_node = (id) => ({
@@ -242,7 +242,7 @@ window.ibc = (() => {
                     } else if (p < 0) {
                         nodes[p] = create_node(p);
                     } else {
-                        create_node_rec(SugarCube.State.variables.slaves[SugarCube.State.variables.slaveIndices[p]]);
+                        create_node_rec(find_gp(p));
                     }
                 }
             });
@@ -252,8 +252,9 @@ window.ibc = (() => {
             nodes[s.ID].mother = (m === null) ? m : nodes[m];
             nodes[s.ID].father = (f === null) ? f : nodes[f];
 
-            if ("inbreedingCoeff" in s && s.inbreedingCoeff !== -1) {
-                nodes[s.ID]._coeff = s.inbreedingCoeff;
+            let sg = find_gp(s.ID);
+            if ("inbreedingCoeff" in sg && sg.inbreedingCoeff !== -1) {
+                nodes[s.ID]._coeff = sg.inbreedingCoeff;
             }
         };
 
@@ -280,7 +281,7 @@ window.ibc = (() => {
         Object.keys(nodes).forEach(s => {
             let n = nodes[s];
             if (n.id in SugarCube.State.variables.slaveIndices) {
-                let slave = SugarCube.State.variables.slaves[SugarCube.State.variables.slaveIndices[n.id]];
+                let slave = find_gp(n.id);
                 if (!("inbreedingCoeff" in slave) || slave.inbreedingCoeff === -1) {
                     slave.inbreedingCoeff = n._coeff;
                 }