diff --git a/data/scenarios/Challenges/_dna/solution.sw b/data/scenarios/Challenges/_dna/solution.sw
index 5a384bdf5..76331ee86 100644
--- a/data/scenarios/Challenges/_dna/solution.sw
+++ b/data/scenarios/Challenges/_dna/solution.sw
@@ -1,5 +1,53 @@
 def doN = \n. \f. if (n > 0) {f; doN (n - 1) f} {}; end;
 
+def getBaseForNumber = \n.
+    if (n == 0) {
+        "guanine";
+    } {
+        if (n == 1) {
+            "cytosine";
+        } {
+            if (n == 2) {
+                "adenine";
+            } {
+                "thymine";
+            };
+        };
+    };
+    end;
+
+def getNumberForBase = \n.
+    if (n == "guanine") {
+        0;
+    } {
+        if (n == "cytosine") {
+            1;
+        } {
+            if (n == "adenine") {
+                2;
+            } {
+                3;
+            };
+        };
+    };
+    end;
+
+def getComplementNumber = \n.
+    if (n == 0) {
+        1;
+    } {
+        if (n == 1) {
+            0;
+        } {
+            if (n == 2) {
+                3;
+            } {
+                2;
+            };
+        };
+    };
+    end;
+
 def waitWhileHere = \item.
     stillHere <- ishere item;
     if stillHere {
@@ -24,12 +72,16 @@ def moveToPattern =
     turn right;
     doN 2 move;
     turn right;
-    doN 5 move;
+    doN 4 move;
+    turn right;
+    move;
+    turn left;
+    move;
     end;
 
 def moveToOtherRow =
     turn right;
-    doN 9 move;
+    doN 8 move;
     turn right;
     move;
     end;
@@ -39,13 +91,22 @@ def waitForItem : Dir -> Cmd Text = \d.
     case item (\_. waitForItem d) return;
     end;
 
+
+def placeComplementOf = \item.
+    let baseNumber = getNumberForBase item in
+    let complementNumber = getComplementNumber baseNumber in
+    let newItem = getBaseForNumber complementNumber in
+    place newItem;
+    end;
+
 /**
 Store the observed entities in the recursion stack.
 */
 def replicatePattern = \standbyFunc. \n.
     if (n > 0) {
-        thingTemp <- waitForItem down;
+        thingTemp <- waitForItem left;
         let thing = thingTemp in
+        placeComplementOf thing;
         move;
         replicatePattern standbyFunc $ n - 1;
 
@@ -58,9 +119,11 @@ def replicatePattern = \standbyFunc. \n.
 
 def go =
     move;
-
     let sentinel = "flower" in
     place sentinel;
+
+    doN 16 $ make "cytosine";
+
     waitWhileHere sentinel;
     moveToPattern;
     replicatePattern moveToOtherRow 32;
diff --git a/data/scenarios/Challenges/_dna/topchecker.sw b/data/scenarios/Challenges/_dna/topchecker.sw
new file mode 100644
index 000000000..86ddc1dc8
--- /dev/null
+++ b/data/scenarios/Challenges/_dna/topchecker.sw
@@ -0,0 +1,90 @@
+def doN = \n. \f. if (n > 0) {f; doN (n - 1) f} {}; end;
+
+def getBaseForNumber = \n.
+    if (n == 0) {
+        "guanine";
+    } {
+        if (n == 1) {
+            "cytosine";
+        } {
+            if (n == 2) {
+                "adenine";
+            } {
+                "thymine";
+            };
+        };
+    };
+    end;
+
+def getNumberForBase = \n.
+    if (n == "guanine") {
+        0;
+    } {
+        if (n == "cytosine") {
+            1;
+        } {
+            if (n == "adenine") {
+                2;
+            } {
+                if (n == "thymine") {
+                    3;
+                } {-1};
+            };
+        };
+    };
+    end;
+
+def getComplementNumber = \n.
+    if (n == 0) {
+        1;
+    } {
+        if (n == 1) {
+            0;
+        } {
+            if (n == 2) {
+                3;
+            } {
+                2;
+            };
+        };
+    };
+    end;
+
+def waitUntilHere = \remainingCount.
+    if (remainingCount > 0) {
+        maybeItemHere <- scan down;
+        case maybeItemHere (\_. 
+            watch down;
+            wait 1000;
+            waitUntilHere remainingCount;
+        ) (\itemHere.
+
+            maybeItemAbove <- scan left;
+            case maybeItemAbove (\_. fail "Expected an item here.") (\itemAbove.
+                let num = getNumberForBase itemAbove in
+                if (num >= 0) {
+                    let complementNum = getComplementNumber num in
+                    let complementItem = getBaseForNumber complementNum in
+                    if (complementItem == itemHere) {
+                        move;
+                        waitUntilHere $ remainingCount - 1;
+                    } {
+                        create "pixel (R)";
+                    }
+                } {
+                    fail "Expected nonnegative item index."
+                }
+            );
+        );
+    } {
+        log "Finished verifying top row";
+        create "pixel (G)";
+    };
+
+    end;
+
+def go =
+    instant $ waitUntilHere 32;
+    end;
+
+go;
\ No newline at end of file
diff --git a/data/scenarios/Challenges/_dna/verifier.sw b/data/scenarios/Challenges/_dna/verifier.sw
index 4a58d3d05..ef11b9e20 100644
--- a/data/scenarios/Challenges/_dna/verifier.sw
+++ b/data/scenarios/Challenges/_dna/verifier.sw
@@ -162,22 +162,20 @@ def spawnComplementer =
 
 def makeDnaStrand =
     teleport self (5, -2);
-    r <- spawnComplementer;
     clonedOrganism <- placeBase myStandby 32;
     doN 3 move;
     drill forward;
     teleport self (36, -12);
-    give r "gold coin";
 
     return clonedOrganism
     end;
 
 def go =
     instant $ waitUntilHere "flower";
-    // _f <- grab;
+    create "pixel (G)";
     clonedOrganism <- makeDnaStrand;
-    teleport self (40, -13);
-    place clonedOrganism;
+    // teleport self (40, -13);
+    // place clonedOrganism;
     end;
 
 go;
\ No newline at end of file
diff --git a/data/scenarios/Challenges/dna.yaml b/data/scenarios/Challenges/dna.yaml
index feac3059d..2ebbe3cbc 100644
--- a/data/scenarios/Challenges/dna.yaml
+++ b/data/scenarios/Challenges/dna.yaml
@@ -14,17 +14,21 @@ objectives:
     condition: |
       r <- robotnamed "verifier";
       as r {
-        has "flower";
+        has "pixel (G)";
       }
   - goal:
       - |
         You must complete the DNA strand with complementary base pairs.
-
-        Pick up the result of the cloning experiment to win.
     condition: |
-      as base {
-        has "organic sludge";
+      r <- robotnamed "topchecker";
+      as r {
+        has "pixel (G)";
       }
+  - goal:
+      - |
+        Pick up the result of the cloning experiment to win.
+    condition: |
+      return false;
 robots:
   - name: base
     dir: east
@@ -34,28 +38,27 @@ robots:
       - branch predictor
       - comparator
       - dictionary
+      - feeler
       - switch puller
       - grabber
       - hearing aid
       - lambda
       - logger
+      - microscope
       - rolex
-      - scanner
       - strange loop
       - treads
       - welder
       - workbench
     inventory:
       - [1, flower]
-      - [64, guanine]
-      - [64, cytosine]
-      - [64, adenine]
-      - [64, thymine]
+      - [32, pipette]
+      - [16, primordial soup]
   - name: verifier
     system: true
     dir: east
     display:
-      invisible: true
+      invisible: false
       attr: 'robot'
     devices:
       - switch puller
@@ -85,9 +88,47 @@ robots:
       - [1, solar panel]
     program: |
       run "data/scenarios/Challenges/_dna/verifier.sw"
+  - name: topchecker
+    system: true
+    dir: east
+    display:
+      invisible: false
+      attr: 'robot'
+    program: |
+      run "data/scenarios/Challenges/_dna/topchecker.sw"
 solution: |
   run "data/scenarios/Challenges/_dna/solution.sw"
 entities:
+  - name: primordial soup
+    display:
+      char: 's'
+    description:
+      - Can be decomposed into nucleic acids
+    properties: [known, pickable]
+  - name: feeler
+    display:
+      char: 'm'
+    description:
+      - Senses presense of specific entities
+    properties: [known, pickable]
+    capabilities: [blocked, ishere, isempty]
+  - name: microscope
+    display:
+      char: 'm'
+    description:
+      - Scan for the cost of 1 `pipette`{=entity}
+    properties: [known, pickable]
+    capabilities:
+      - capability: scan
+        cost:
+          - [1, "pipette"]
+  - name: pipette
+    display:
+      char: 'p'
+      attr: ice
+    description:
+      - One of the four nucleobases in DNA.
+      - Is paired with "cytosine".
   - name: guanine
     display:
       char: 'G'
@@ -95,7 +136,7 @@ entities:
     description:
       - One of the four nucleobases in DNA.
       - Is paired with "cytosine".
-    properties: [pickable, known]
+    properties: [known]
   - name: cytosine
     display:
       char: 'C'
@@ -103,7 +144,7 @@ entities:
     description:
       - One of the four nucleobases in DNA.
       - Is paired with "guanine".
-    properties: [pickable, known]
+    properties: [known]
   - name: adenine
     display:
       char: 'A'
@@ -111,7 +152,7 @@ entities:
     description:
       - One of the four nucleobases in DNA.
       - Is paired with "thymine".
-    properties: [pickable, known]
+    properties: [known]
   - name: thymine
     display:
       char: 'T'
@@ -119,7 +160,7 @@ entities:
     description:
       - One of the four nucleobases in DNA.
       - Is paired with "adenine".
-    properties: [pickable, known]
+    properties: [known]
   - name: switch (off)
     display:
       attr: red
@@ -149,6 +190,13 @@ entities:
     description:
       - Can pull switches
 recipes:
+  - in:
+      - [1, primordial soup]
+    out:
+      - [4, cytosine]
+      - [4, guanine]
+      - [4, adenine]
+      - [4, thymine]
   - in:
       - [1, switch (off)]
     out:
@@ -187,9 +235,10 @@ world:
   palette:
     '┬': [stone, down and horizontal wall]
     '┴': [stone, up and horizontal wall]
+    'z': [stone, wall]
     '.': [stone, erase]
     ':': [blank, erase]
-    'z': [stone, wall]
+    'c': [blank, erase, topchecker]
     'v': [stone, erase, verifier]
     'B': [stone, erase, base]
     '0': [stone, switch (off)]
@@ -199,7 +248,7 @@ world:
     z...........................................z
     z.....┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬┬......z
     z.....::::::::::::::::::::::::::::::::......z
-    z.zz..::::::::::::::::::::::::::::::::......z
+    z.zz..c:::::::::::::::::::::::::::::::......z
     zBvzzz┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴┴......z
     z.zz........................................z
     z...........................................z