diff --git a/.changeset/fix-sc-tcr-chain-letters.md b/.changeset/fix-sc-tcr-chain-letters.md
new file mode 100644
index 0000000..0d4e0fd
--- /dev/null
+++ b/.changeset/fix-sc-tcr-chain-letters.md
@@ -0,0 +1,8 @@
+---
+'@platforma-open/milaboratories.vj-usage.ui': minor
+'@platforma-open/milaboratories.vj-usage': minor
+---
+
+Fix single-cell TCR chain selector mapping: A/B were swapped for TCRAB and TCRGD. Producers (mixcr-clonotyping, import-vdj-data) assign A to the more diverse chains: Beta and Delta. The selector was running usage on the opposite chain from the one labelled. Existing blocks are relabelled only, the stored chain value is unchanged, so nothing re-runs.
+
+The selector also lists chains in the classic annotation order again — Alpha/Beta and Gamma/Delta — instead of the value order A/B.
diff --git a/ui/src/utils.ts b/ui/src/utils.ts
index c8966cb..01f24ef 100644
--- a/ui/src/utils.ts
+++ b/ui/src/utils.ts
@@ -32,6 +32,8 @@ export function useScChainOptions(
 
     const receptor = axisSpec.domain?.["pl7.app/vdj/receptor"];
 
+    // Values are the producers' (mixcr-clonotyping, import-vdj-data): A is the more diverse
+    // chain. Array order is display order, kept in the classic annotation order.
     let options: { label: string; value: string }[];
     switch (receptor) {
       case "IG":
@@ -42,14 +44,14 @@ export function useScChainOptions(
         break;
       case "TCRAB":
         options = [
-          { label: "Alpha", value: "A" },
-          { label: "Beta", value: "B" },
+          { label: "Alpha", value: "B" },
+          { label: "Beta", value: "A" },
         ];
         break;
       case "TCRGD":
         options = [
-          { label: "Gamma", value: "A" },
-          { label: "Delta", value: "B" },
+          { label: "Gamma", value: "B" },
+          { label: "Delta", value: "A" },
         ];
         break;
       default: