diff --git a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/genotyper/GenotypingEngine.java b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/genotyper/GenotypingEngine.java
index ce616377d..6f11fe949 100644
--- a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/genotyper/GenotypingEngine.java
+++ b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/genotyper/GenotypingEngine.java
@@ -87,7 +87,7 @@ public abstract class GenotypingEngine<Config extends StandardCallerArgumentColl
 
     protected final Config configuration;
 
-    protected final VariantAnnotatorEngine annotationEngine;
+    protected VariantAnnotatorEngine annotationEngine;
 
     protected final int numberOfGenomes;
 
@@ -108,26 +108,49 @@ public abstract class GenotypingEngine<Config extends StandardCallerArgumentColl
             return AFCalcFactory.createAFCalc(configuration, numberOfGenomes, logger);
         }
     };
-
     /**
      * Construct a new genotyper engine.
      *
      * @param toolkit reference to the genome-analysis toolkit.
      * @param configuration engine configuration object.
-     * @param annotationEngine reference to the annotation engine. If {@code null}, no annotations will be processed.
+     *
+     * @throws IllegalArgumentException if either {@code toolkit} or {@code configuration} is {@code null}.
+     */
+    protected GenotypingEngine(final GenomeAnalysisEngine toolkit, final Config configuration) {
+        this(toolkit,configuration,resolveSampleNamesFromToolkit(toolkit));
+    }
+
+    /**
+     * Resolve the sample name set to be the set of all samples passed to the tool.
+     *
+     * @param toolkit reference to the toolkit.
+     *
+     * @throws IllegalArgumentException if the {@code toolkit} is {@code null}.
+     *
+     * @return never {@code null}, but empty if there is no samples.
+     */
+    private static Set<String> resolveSampleNamesFromToolkit(final GenomeAnalysisEngine toolkit) {
+        if (toolkit == null)
+            throw new IllegalArgumentException("the toolkit cannot be null");
+        return new LinkedHashSet<>(toolkit.getSampleDB().getSampleNames());
+    }
+
+    /**
+     * Construct a new genotyper engine, on a specific subset of samples.
+     *
+     * @param toolkit reference to the genome-analysis toolkit.
+     * @param configuration engine configuration object.
      * @param sampleNames subset of sample to work on identified by their names. If {@code null}, the full toolkit
      *                    sample set will be used instead.
      *
      * @throws IllegalArgumentException if either {@code toolkit} or {@code configuration} is {@code null}.
      */
-    public GenotypingEngine(final GenomeAnalysisEngine toolkit, final Config configuration,
-                            final VariantAnnotatorEngine annotationEngine, final Set<String> sampleNames) {
+    protected GenotypingEngine(final GenomeAnalysisEngine toolkit, final Config configuration,final Set<String> sampleNames) {
         if (toolkit == null)
             throw new IllegalArgumentException("the toolkit cannot be null");
         if (configuration == null)
             throw new IllegalArgumentException("the configuration cannot be null");
         this.configuration = configuration;
-        this.annotationEngine = annotationEngine;
         logger = Logger.getLogger(getClass());
         this.toolkit = toolkit;
         this.sampleNames = sampleNames != null ? sampleNames : toolkit.getSampleDB().getSampleNames();
@@ -152,6 +175,15 @@ public abstract class GenotypingEngine<Config extends StandardCallerArgumentColl
         this.logger = logger;
     }
 
+    /**
+     * Changes the annotation engine for this genotyping-engine.
+     *
+     * @param annotationEngine the new annotation engine (can be {@code null}).
+     */
+    public void setAnnotationEngine(final VariantAnnotatorEngine annotationEngine) {
+        this.annotationEngine = annotationEngine;
+    }
+
     /**
      * Returns a reference to the engine configuration
      *
@@ -350,7 +382,7 @@ public abstract class GenotypingEngine<Config extends StandardCallerArgumentColl
      *
      * @param conf
      * @param PofF
-     * @return {@true} iff the variant is confidently called.
+     * @return {@code true} iff the variant is confidently called.
      */
     protected final boolean confidentlyCalled(final double conf, final double PofF) {
         return conf >= configuration.STANDARD_CONFIDENCE_FOR_CALLING ||
diff --git a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/genotyper/UnifiedGenotyper.java b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/genotyper/UnifiedGenotyper.java
index 2bdeff5db..91b78daaf 100644
--- a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/genotyper/UnifiedGenotyper.java
+++ b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/genotyper/UnifiedGenotyper.java
@@ -283,7 +283,9 @@ public class UnifiedGenotyper extends LocusWalker<List<VariantCallContext>, Unif
             verboseWriter.println("AFINFO\tLOC\tREF\tALT\tMAF\tF\tAFprior\tMLE\tMAP");
 
         annotationEngine = new VariantAnnotatorEngine(Arrays.asList(annotationClassesToUse), annotationsToUse, annotationsToExclude, this, getToolkit());
-        genotypingEngine = new UnifiedGenotypingEngine(getToolkit(), UAC, annotationEngine,samples, verboseWriter);
+        genotypingEngine = new UnifiedGenotypingEngine(getToolkit(), UAC, samples);
+        genotypingEngine.setVerboseWriter(verboseWriter);
+        genotypingEngine.setAnnotationEngine(annotationEngine);
 
         // initialize the header
         Set<VCFHeaderLine> headerInfo = getHeaderInfo(UAC, annotationEngine, dbsnp);
diff --git a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/genotyper/UnifiedGenotypingEngine.java b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/genotyper/UnifiedGenotypingEngine.java
index ba7b76e8e..81eebb6fd 100644
--- a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/genotyper/UnifiedGenotypingEngine.java
+++ b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/genotyper/UnifiedGenotypingEngine.java
@@ -51,7 +51,6 @@ import org.broadinstitute.sting.gatk.contexts.AlignmentContext;
 import org.broadinstitute.sting.gatk.contexts.AlignmentContextUtils;
 import org.broadinstitute.sting.gatk.contexts.ReferenceContext;
 import org.broadinstitute.sting.gatk.refdata.RefMetaDataTracker;
-import org.broadinstitute.sting.gatk.walkers.annotator.VariantAnnotatorEngine;
 import org.broadinstitute.sting.gatk.walkers.genotyper.afcalc.AFCalcResult;
 import org.broadinstitute.sting.utils.BaseUtils;
 import org.broadinstitute.sting.utils.GenomeLocParser;
@@ -76,7 +75,6 @@ import java.util.*;
 public class UnifiedGenotypingEngine extends GenotypingEngine<UnifiedArgumentCollection> {
 
     public static final String LOW_QUAL_FILTER_NAME = "LowQual";
-    private static final String GPSTRING = "GENERALPLOIDY";
 
     public static final String NUMBER_OF_DISCOVERED_ALLELES_KEY = "NDA";
     public static final String PL_FOR_ALL_SNP_ALLELES_KEY = "APL";
@@ -90,7 +88,7 @@ public class UnifiedGenotypingEngine extends GenotypingEngine<UnifiedArgumentCol
 
 
     // the various loggers and writers
-    private final PrintStream verboseWriter;
+    private PrintStream verboseWriter;
 
     private final GenomeLocParser genomeLocParser;
     private final boolean BAQEnabledOnCMDLine;
@@ -112,7 +110,7 @@ public class UnifiedGenotypingEngine extends GenotypingEngine<UnifiedArgumentCol
      * @throws IllegalArgumentException if either {@code toolkit} or {@code UAC} is {@code null}.
      */
     public UnifiedGenotypingEngine(final GenomeAnalysisEngine toolkit, final UnifiedArgumentCollection configuration) {
-        this(toolkit, configuration, null, null, null);
+        this(toolkit, configuration, null);
     }
 
     /**
@@ -120,28 +118,32 @@ public class UnifiedGenotypingEngine extends GenotypingEngine<UnifiedArgumentCol
      *
      * @param toolkit reference to the enclosing genome analysis engine.
      * @param configuration configuration object.
-     * @param annotationEngine variant annotation engine. If {@code null}, no annotations will be processed.
      * @param sampleNames subset of sample names to work on. If {@code null}, all it will use the {@code toolkit} full sample set.
-     * @param verboseWriter where to output additional verbose debugging information.
      *
      * @throws IllegalArgumentException if either {@code toolkit} or {@code UAC} is {@code null}.
      */
     public UnifiedGenotypingEngine(final GenomeAnalysisEngine toolkit, final UnifiedArgumentCollection configuration,
-                                   final VariantAnnotatorEngine annotationEngine,
-                                   final Set<String> sampleNames, final PrintStream verboseWriter) {
+                                   final Set<String> sampleNames) {
 
-        super(toolkit,configuration,annotationEngine,sampleNames);
+        super(toolkit,configuration,sampleNames);
 
         this.BAQEnabledOnCMDLine = toolkit.getArguments().BAQMode != BAQ.CalculationMode.OFF;
         genomeLocParser = toolkit.getGenomeLocParser();
 
-        this.verboseWriter = verboseWriter;
-
         determineGLModelsToUse();
 
         initializeGenotypeLikelihoodsCalculationModels();
     }
 
+    /**
+     * Changes the verbose output writer for this engine.
+     *
+     * @param writer the new writer; it can be {@code null}.
+     */
+    public void setVerboseWriter(final PrintStream writer) {
+        verboseWriter = writer;
+    }
+
     /**
      * Initialize {@link #glcm}.
      */
diff --git a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/haplotypecaller/HaplotypeCaller.java b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/haplotypecaller/HaplotypeCaller.java
index 3e3b76d71..7a25e8bc8 100644
--- a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/haplotypecaller/HaplotypeCaller.java
+++ b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/haplotypecaller/HaplotypeCaller.java
@@ -569,7 +569,7 @@ public class HaplotypeCaller extends ActiveRegionWalker<List<VariantContext>, In
         simpleUAC.CONTAMINATION_FRACTION = 0.0;
         simpleUAC.CONTAMINATION_FRACTION_FILE = null;
         simpleUAC.exactCallsLog = null;
-        activeRegionEvaluationGenotyperEngine = new UnifiedGenotypingEngine(getToolkit(), simpleUAC, null, samplesSet, null);
+        activeRegionEvaluationGenotyperEngine = new UnifiedGenotypingEngine(getToolkit(), simpleUAC, samplesSet);
         activeRegionEvaluationGenotyperEngine.setLogger(logger);
 
         if( SCAC.CONTAMINATION_FRACTION_FILE != null )
@@ -644,7 +644,10 @@ public class HaplotypeCaller extends ActiveRegionWalker<List<VariantContext>, In
 
         final MergeVariantsAcrossHaplotypes variantMerger = mergeVariantsViaLD ? new LDMerger(SCAC.DEBUG, 10, 1) : new MergeVariantsAcrossHaplotypes();
 
-        genotypingEngine = new HaplotypeCallerGenotypingEngine( getToolkit(),SCAC, annotationEngine, null, variantMerger );
+        genotypingEngine = new HaplotypeCallerGenotypingEngine( getToolkit(),SCAC);
+        genotypingEngine.setCrossHaplotypeEventMerger(variantMerger);
+
+        genotypingEngine.setAnnotationEngine(annotationEngine);
 
         if ( bamWriter != null ) {
             // we currently do not support multi-threaded BAM writing, so exception out
diff --git a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/haplotypecaller/HaplotypeCallerGenotypingEngine.java b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/haplotypecaller/HaplotypeCallerGenotypingEngine.java
index fa743813a..907e8a07e 100644
--- a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/haplotypecaller/HaplotypeCallerGenotypingEngine.java
+++ b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/haplotypecaller/HaplotypeCallerGenotypingEngine.java
@@ -48,10 +48,8 @@ package org.broadinstitute.sting.gatk.walkers.haplotypecaller;
 
 import com.google.java.contract.Ensures;
 import com.google.java.contract.Requires;
-import org.apache.log4j.Logger;
 import org.broadinstitute.sting.gatk.GenomeAnalysisEngine;
 import org.broadinstitute.sting.gatk.refdata.RefMetaDataTracker;
-import org.broadinstitute.sting.gatk.walkers.annotator.VariantAnnotatorEngine;
 import org.broadinstitute.sting.gatk.walkers.genotyper.GenotypeLikelihoodsCalculationModel;
 import org.broadinstitute.sting.gatk.walkers.genotyper.GenotypingEngine;
 import org.broadinstitute.sting.gatk.walkers.genotyper.GenotypingOutputMode;
@@ -75,16 +73,36 @@ import java.util.*;
  */
 public class HaplotypeCallerGenotypingEngine extends GenotypingEngine<HaplotypeCallerArgumentCollection> {
 
-    private final static Logger logger = Logger.getLogger(HaplotypeCallerGenotypingEngine.class);
-
     private final static List<Allele> NO_CALL = Collections.singletonList(Allele.NO_CALL);
 
-    private final MergeVariantsAcrossHaplotypes crossHaplotypeEventMerger;
+    private MergeVariantsAcrossHaplotypes crossHaplotypeEventMerger;
 
-    public HaplotypeCallerGenotypingEngine(final GenomeAnalysisEngine toolkit, final HaplotypeCallerArgumentCollection configuration,
-                                           final VariantAnnotatorEngine annotationEngine, final Set<String> sampleNames,
-                                           final MergeVariantsAcrossHaplotypes crossHaplotypeEventMerger) {
-        super(toolkit,configuration,annotationEngine,sampleNames);
+    /**
+     * {@inheritDoc}
+     * @param toolkit {@inheritDoc}
+     * @param configuration {@inheritDoc}
+     */
+    public HaplotypeCallerGenotypingEngine(final GenomeAnalysisEngine toolkit, final HaplotypeCallerArgumentCollection configuration) {
+        super(toolkit,configuration);
+    }
+
+    /**
+     * {@inheritDoc}
+     * @param toolkit {@inheritDoc}
+     * @param configuration {@inheritDoc}
+     * @param sampleNames {@inheritDoc}
+     */
+    public HaplotypeCallerGenotypingEngine(final GenomeAnalysisEngine toolkit, final HaplotypeCallerArgumentCollection configuration, final Set<String> sampleNames) {
+        super(toolkit,configuration,sampleNames);
+    }
+
+
+    /**
+     * Change the merge variant across haplotypes for this engine.
+     *
+     * @param crossHaplotypeEventMerger new merger, can be {@code null}.
+     */
+    public void setCrossHaplotypeEventMerger(final MergeVariantsAcrossHaplotypes crossHaplotypeEventMerger) {
         this.crossHaplotypeEventMerger = crossHaplotypeEventMerger;
     }
 
@@ -227,8 +245,8 @@ public class HaplotypeCallerGenotypingEngine extends GenotypingEngine<HaplotypeC
 
                 final Map<Allele, List<Haplotype>> alleleMapper = createAlleleMapper(mergeMap, eventMapper);
 
-                if( configuration.DEBUG ) {
-                    logger.info("Genotyping event at " + loc + " with alleles = " + mergedVC.getAlleles());
+                if( configuration.DEBUG && logger != null ) {
+                    if (logger != null) logger.info("Genotyping event at " + loc + " with alleles = " + mergedVC.getAlleles());
                 }
 
                 final Map<String, PerReadAlleleLikelihoodMap> alleleReadMap = convertHaplotypeReadMapToAlleleReadMap(haplotypeReadMap, alleleMapper, configuration.getSampleContamination());
@@ -314,6 +332,8 @@ public class HaplotypeCallerGenotypingEngine extends GenotypingEngine<HaplotypeC
         //cleanUpSymbolicUnassembledEvents( haplotypes ); // We don't make symbolic alleles so this isn't needed currently
         if ( !in_GGA_mode ) {
             // run the event merger if we're not in GGA mode
+            if (crossHaplotypeEventMerger == null)
+                throw new IllegalStateException(" no variant merger was provided at set-up when needed in GGA mode");
             final boolean mergedAnything = crossHaplotypeEventMerger.merge(haplotypes, haplotypeReadMap, startPosKeySet, ref, refLoc);
             if ( mergedAnything )
                 cleanUpSymbolicUnassembledEvents( haplotypes ); // the newly created merged events could be overlapping the unassembled events
diff --git a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/variantutils/GenotypeGVCFs.java b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/variantutils/GenotypeGVCFs.java
index a9cd6d101..ac9b8c4fa 100644
--- a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/variantutils/GenotypeGVCFs.java
+++ b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/variantutils/GenotypeGVCFs.java
@@ -167,7 +167,7 @@ public class GenotypeGVCFs extends RodWalker<VariantContext, VariantContextWrite
         vcfWriter.writeHeader(vcfHeader);
 
         // create the genotyping engine
-        genotypingEngine = new UnifiedGenotypingEngine(getToolkit(), new UnifiedArgumentCollection(),null,samples,null);
+        genotypingEngine = new UnifiedGenotypingEngine(getToolkit(), new UnifiedArgumentCollection(),samples);
 
         // collect the actual rod bindings into a list for use later
         for ( final RodBindingCollection<VariantContext> variantCollection : variantCollections )
diff --git a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/variantutils/RegenotypeVariants.java b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/variantutils/RegenotypeVariants.java
index 2cb12878b..97bb8166a 100644
--- a/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/variantutils/RegenotypeVariants.java
+++ b/protected/gatk-protected/src/main/java/org/broadinstitute/sting/gatk/walkers/variantutils/RegenotypeVariants.java
@@ -121,7 +121,7 @@ public class RegenotypeVariants extends RodWalker<Integer, Integer> implements T
 
         String trackName = variantCollection.variants.getName();
         Set<String> samples = SampleUtils.getSampleListWithVCFHeader(getToolkit(), Arrays.asList(trackName));
-        UG_engine = new UnifiedGenotypingEngine(getToolkit(), UAC, null, samples, null);
+        UG_engine = new UnifiedGenotypingEngine(getToolkit(), UAC, samples);
 
         final Set<VCFHeaderLine> hInfo = new HashSet<VCFHeaderLine>();
         hInfo.addAll(GATKVCFUtils.getHeaderFields(getToolkit(), Arrays.asList(trackName)));
diff --git a/protected/gatk-protected/src/test/java/org/broadinstitute/sting/gatk/walkers/genotyper/UnifiedGenotyperEngineUnitTest.java b/protected/gatk-protected/src/test/java/org/broadinstitute/sting/gatk/walkers/genotyper/UnifiedGenotyperEngineUnitTest.java
index 54b5637de..e05cb89cc 100644
--- a/protected/gatk-protected/src/test/java/org/broadinstitute/sting/gatk/walkers/genotyper/UnifiedGenotyperEngineUnitTest.java
+++ b/protected/gatk-protected/src/test/java/org/broadinstitute/sting/gatk/walkers/genotyper/UnifiedGenotyperEngineUnitTest.java
@@ -78,7 +78,7 @@ public class UnifiedGenotyperEngineUnitTest extends BaseTest {
         final UnifiedArgumentCollection args = new UnifiedArgumentCollection();
         final Set<String> fakeSamples = Collections.singleton("fake");
 
-        ugEngine = new UnifiedGenotypingEngine(engine, args, null, fakeSamples, null);
+        ugEngine = new UnifiedGenotypingEngine(engine, args,fakeSamples);
     }
 
     private UnifiedGenotypingEngine getEngine() {