diff --git a/java/src/org/broadinstitute/sting/playground/gatk/walkers/PoolCaller.java b/java/src/org/broadinstitute/sting/playground/gatk/walkers/PoolCaller.java
index 7c2a2c90b..a2001b845 100644
--- a/java/src/org/broadinstitute/sting/playground/gatk/walkers/PoolCaller.java
+++ b/java/src/org/broadinstitute/sting/playground/gatk/walkers/PoolCaller.java
@@ -98,6 +98,8 @@ public class PoolCaller extends LocusWalker<AlleleFrequencyEstimate, String>
 
     public AlleleFrequencyEstimate map(RefMetaDataTracker tracker, char ref, LocusContext context) 
     {
+		if (ref == 'N') { return null; }
+
         // 1. seperate each context.
         LocusContext[] contexts = filterLocusContext(context, sample_names, 0);
 
@@ -114,7 +116,31 @@ public class PoolCaller extends LocusWalker<AlleleFrequencyEstimate, String>
         double[] trajectory = new double[MAX_ITERATIONS + 1]; trajectory[0] = EM_alt_freq;
         double[] likelihood_trajectory = new double[MAX_ITERATIONS + 1]; likelihood_trajectory[0] = 0.0;
         boolean is_a_snp = false;
+
+		// Pick the alternate base
 		char alt = 'N';
+		{
+        	ReadBackedPileup pileup = new ReadBackedPileup(ref, context);
+			String bases = pileup.getBases();
+			int A = 0;
+			int C = 0;
+			int G = 0; 
+			int T = 0;
+			int max_count = -1;
+			for (int i = 0; i < bases.length(); i++)
+			{
+				char b = bases.charAt(i);
+				if (b == ref) { continue; }
+				switch (b)
+				{
+					case 'A' : A += 1; if (A > max_count) { max_count = A; alt = 'A'; } break;
+					case 'C' : C += 1; if (C > max_count) { max_count = C; alt = 'C'; } break;
+					case 'G' : G += 1; if (G > max_count) { max_count = G; alt = 'G'; } break;
+					case 'T' : T += 1; if (T > max_count) { max_count = T; alt = 'T'; } break;
+				}
+			}
+		}
+
         for (int iterations = 0; iterations < MAX_ITERATIONS; iterations++)
         { 
 	        // 6. Re-call from shallow coverage using the estimated frequency as a prior, 
@@ -128,12 +154,10 @@ public class PoolCaller extends LocusWalker<AlleleFrequencyEstimate, String>
 
 	        for (int i = 0; i < sample_names.size(); i++)
 	        {
-	                callers.get(i).setAlleleFrequencyPrior(EM_alt_freq);
+	                callers.get(i).setAlleleFrequencyPrior(EM_alt_freq, alt);
 	                calls[i] = callers.get(i).map(tracker, ref, contexts[i]);
 	                String genotype = calls[i].genotype();
 
-					if (calls[i].alt != 'N') { alt = calls[i].alt; }
-
                     likelihood += calls[i].pBest;
 	
                     if (! FRACTIONAL_COUNTS)
@@ -157,7 +181,7 @@ public class PoolCaller extends LocusWalker<AlleleFrequencyEstimate, String>
                     }   
 
             }
-	        EM_alt_freq = EM_sum / EM_N;
+	        EM_alt_freq = Math.min(EM_sum / EM_N, 0.99999);
             trajectory[iterations+1] = EM_alt_freq;
             likelihood_trajectory[iterations+1] = likelihood;
 
diff --git a/java/src/org/broadinstitute/sting/playground/gatk/walkers/SingleSampleGenotyper.java b/java/src/org/broadinstitute/sting/playground/gatk/walkers/SingleSampleGenotyper.java
index 5a0c4453d..761b7d1f0 100644
--- a/java/src/org/broadinstitute/sting/playground/gatk/walkers/SingleSampleGenotyper.java
+++ b/java/src/org/broadinstitute/sting/playground/gatk/walkers/SingleSampleGenotyper.java
@@ -278,6 +278,12 @@ public class SingleSampleGenotyper extends LocusWalker<AlleleFrequencyEstimate,
         ReadBackedPileup pileup = new ReadBackedPileup(ref, context);
         String bases = pileup.getBases();
 
+		if (bases.length() == 0)
+		{
+	        GenotypeLikelihoods G = new GenotypeLikelihoods();
+	        return G.toAlleleFrequencyEstimate(context.getLocation(), ref, bases.length(), bases, G.likelihoods, sample_name);
+		}
+
         List<SAMRecord> reads = context.getReads();
         List<Integer> offsets = context.getOffsets();
         ref = Character.toUpperCase(ref);
@@ -305,7 +311,7 @@ public class SingleSampleGenotyper extends LocusWalker<AlleleFrequencyEstimate,
 
             G.add(ref, read.getReadString().charAt(offset), read.getBaseQualities()[offset]);
         }
-        G.ApplyPrior(ref, this.allele_frequency_prior);
+        G.ApplyPrior(ref, this.alt_allele, this.allele_frequency_prior);
 
         if (fourBaseMode) {
             G.applyFourBaseDistributionPrior(pileup.getBases(), pileup.getSecondaryBasePileup());
@@ -333,9 +339,11 @@ public class SingleSampleGenotyper extends LocusWalker<AlleleFrequencyEstimate,
     }
 
     double allele_frequency_prior = -1;
-    public void setAlleleFrequencyPrior(double freq)
+	char alt_allele;
+    public void setAlleleFrequencyPrior(double freq, char alt)
     {
         this.allele_frequency_prior = freq;
+		this.alt_allele = alt;
     }
 
     // Given result of map function
diff --git a/java/src/org/broadinstitute/sting/playground/utils/GenotypeLikelihoods.java b/java/src/org/broadinstitute/sting/playground/utils/GenotypeLikelihoods.java
index a5ac63319..5397513a3 100644
--- a/java/src/org/broadinstitute/sting/playground/utils/GenotypeLikelihoods.java
+++ b/java/src/org/broadinstitute/sting/playground/utils/GenotypeLikelihoods.java
@@ -137,18 +137,24 @@ public class GenotypeLikelihoods {
         return s;
     }
 
-    public void ApplyPrior(char ref, double p_alt) 
+    public void ApplyPrior(char ref, char alt, double p_alt) 
     {
-        for (int i = 0; i < genotypes.length; i++) {
+        for (int i = 0; i < genotypes.length; i++) 
+		{
             if ((p_alt == -1) || (p_alt <= 1e-6))
             {
-	            if ((genotypes[i].charAt(0) == ref) && (genotypes[i].charAt(1) == ref)) {
+	            if ((genotypes[i].charAt(0) == ref) && (genotypes[i].charAt(1) == ref)) 
+				{
 	                // hom-ref
 	                likelihoods[i] += Math.log10(1.0 - 1e-3);
-	            } else if ((genotypes[i].charAt(0) != ref) && (genotypes[i].charAt(1) != ref)) {
+	            } 
+				else if ((genotypes[i].charAt(0) != ref) && (genotypes[i].charAt(1) != ref)) 
+				{
 	                // hom-nonref
 	                likelihoods[i] += Math.log10(1e-5);
-	            } else {
+	            } 
+				else 
+				{
 	                // het
 	                likelihoods[i] += Math.log10(1e-3);
 	            }
@@ -156,16 +162,27 @@ public class GenotypeLikelihoods {
             }
             else
             {
-	            if ((genotypes[i].charAt(0) == ref) && (genotypes[i].charAt(1) == ref)) {
+	            if ((genotypes[i].charAt(0) == ref) && (genotypes[i].charAt(1) == ref)) 
+				{
 	                // hom-ref
 	                likelihoods[i] += 2.0 * Math.log10(1.0 - p_alt);
-	            } else if ((genotypes[i].charAt(0) != ref) && (genotypes[i].charAt(1) != ref)) {
+	            } 
+				else if ((genotypes[i].charAt(0) == alt) && (genotypes[i].charAt(1) == alt)) 
+				{
 	                // hom-nonref
 	                likelihoods[i] += 2.0 * Math.log10(p_alt);
-	            } else {
+	            } 
+				else if (((genotypes[i].charAt(0) == alt) && (genotypes[i].charAt(1) == ref)) ||
+						 ((genotypes[i].charAt(0) == ref) && (genotypes[i].charAt(1) == alt)))
+				{
 	                // het
 	                likelihoods[i] += Math.log10((1.0-p_alt) * p_alt * 2.0);
 	            }
+				else
+				{
+					// something else (noise!)
+					likelihoods[i] += Math.log10(1e-5);
+				}
 
                 if (Double.isInfinite(likelihoods[i])) { likelihoods[i] = -1000; }
             }