diff --git a/java/src/org/broadinstitute/sting/utils/sam/AlignmentUtils.java b/java/src/org/broadinstitute/sting/utils/sam/AlignmentUtils.java
index 3bd3b5350..754a66029 100644
--- a/java/src/org/broadinstitute/sting/utils/sam/AlignmentUtils.java
+++ b/java/src/org/broadinstitute/sting/utils/sam/AlignmentUtils.java
@@ -64,6 +64,24 @@ public class AlignmentUtils {
         return getMismatchCount(r, refSeq, refIndex).numMismatches;
     }
 
+    /** Same as #numMismatches(SAMRecord, byte[], refIndex), but counts mismatches only along the partial stretch
+     * on the read of length <code>nReadBases</code> starting at (0-based) position <code>readIndex</code>.
+     * @param r Aligned read to count mismatches for
+     * @param refSeq Chunk of reference sequence that subsumes the alignment
+     * @param refIndex Zero-based position on <code>refSeq</code> where the alighnment for the whole read starts
+     * @param readIndex Zero-based position on the read, the mismatches will be counted only from this position on
+     * @param nReadBases Length of continuous stretch on the read, along which mismatches will be counted 
+     * @return
+     */
+    public static int numMismatches(SAMRecord r, byte[] refSeq, int refIndex, int readIndex, int nReadBases) {
+        if ( r.getReadUnmappedFlag() ) return 1000000;
+        return getMismatchCount(r, refSeq, refIndex,readIndex,nReadBases).numMismatches;
+    }
+
+    public static long mismatchingQualities(SAMRecord r, byte[] refSeq, int refIndex, int readIndex, int nReadBases) {
+        return getMismatchCount(r, refSeq, refIndex,readIndex,nReadBases).mismatchQualities;
+    }
+
     @Deprecated
     public static int numMismatches(SAMRecord r, String refSeq, int refIndex ) {
         if ( r.getReadUnmappedFlag() ) return 1000000;
@@ -80,21 +98,31 @@ public class AlignmentUtils {
         return numMismatches(r, StringUtil.stringToBytes(refSeq), refIndex);
      }
 
+    private static MismatchCount getMismatchCount(SAMRecord r, byte[] refSeq, int refIndex) {
+        return getMismatchCount(r,refSeq,refIndex,0,r.getReadLength());
+    }
+
     // todo -- this code and mismatchesInRefWindow should be combined and optimized into a single
     // todo -- high performance implementation.  We can do a lot better than this right now
-    private static MismatchCount getMismatchCount(SAMRecord r, byte[] refSeq, int refIndex) {
+    private static MismatchCount getMismatchCount(SAMRecord r, byte[] refSeq, int refIndex, int startOnRead, int nReadBases) {
         MismatchCount mc = new MismatchCount();
 
         int readIdx = 0;
+        int endOnRead = startOnRead + nReadBases - 1; // index of the last base on read we want to count
         byte[] readSeq = r.getReadBases();
         Cigar c = r.getCigar();
         for (int i = 0 ; i < c.numCigarElements() ; i++) {
+
+            if ( readIdx > endOnRead ) break;
+
             CigarElement ce = c.getCigarElement(i);
             switch ( ce.getOperator() ) {
                 case M:
                     for (int j = 0 ; j < ce.getLength() ; j++, refIndex++, readIdx++ ) {
                         if ( refIndex >= refSeq.length )
                             continue;
+                        if ( readIdx < startOnRead ) continue;
+                        if ( readIdx > endOnRead ) break;
                         byte refChr = refSeq[refIndex];
                         byte readChr = readSeq[readIdx];
                         // Note: we need to count X/N's as mismatches because that's what SAM requires
@@ -337,6 +365,28 @@ public class AlignmentUtils {
         return true;
     }
 
+    /**
+     * Due to (unfortunate) multiple ways to indicate that read/mate is unmapped allowed by SAM format
+     * specification, one may need this convenience shortcut. Checks both 'mate unmapped' flag and
+     * alignment reference index/start of the mate.
+     * @param r sam record for the read
+     * @return true if read's mate is unmapped
+     */
+    public static boolean isMateUnmapped(final SAMRecord r) {
+        if ( r.getMateUnmappedFlag() ) return true;
+
+        // our life would be so much easier if all sam files followed the specs. In reality,
+        // sam files (including those generated by maq or bwa) miss headers alltogether. When
+        // reading such a SAM file, reference name is set, but since there is no sequence dictionary,
+        // null is always returned for referenceIndex. Let's be paranoid here, and make sure that
+        // we do not call the read "unmapped" when it has only reference name set with ref. index missing
+        // or vice versa.
+        if ( ( r.getMateReferenceIndex() != null && r.getMateReferenceIndex() != SAMRecord.NO_ALIGNMENT_REFERENCE_INDEX
+                || r.getMateReferenceName() != null && r.getMateReferenceName() != SAMRecord.NO_ALIGNMENT_REFERENCE_NAME )
+          &&  r.getMateAlignmentStart() != SAMRecord.NO_ALIGNMENT_START ) return false  ;
+        return true;
+    }
+
     /** Returns the array of base qualitites in the order the bases were read on the machine (i.e. always starting from
      * cycle 1). In other words, if the read is unmapped or aligned in the forward direction, the read's own base
      * qualities are returned as stored in the SAM record; if the read is aligned in the reverse direction, the array