diff --git a/Makefile b/Makefile
index 8d2ee0d..44ce80c 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@ CC=			gcc
 CFLAGS=		-g -Wall -O2 -Wc++-compat -Wno-unused-function
 CPPFLAGS=
 INCLUDES=	-I.
-OBJS=		kalloc.o kthread.o misc.o bseq.o sketch.o chain.o sdust.o index.o map.o
+OBJS=		kalloc.o kthread.o misc.o bseq.o sketch.o chain.o align.o sdust.o index.o map.o
 PROG=		minimap2
 PROG_EXTRA=	sdust
 LIBS=		-lm -lz -lpthread
diff --git a/align.c b/align.c
new file mode 100644
index 0000000..d3c04d4
--- /dev/null
+++ b/align.c
@@ -0,0 +1,38 @@
+#include <assert.h>
+#include "minimap.h"
+#include "ksw2.h"
+
+void mm_align_skeleton(void *km, const mm_mapopt_t *opt, const mm_idx_t *mi, int qlen, const char *qstr, int n_regs, mm_reg1_t *regs, mm128_t *a)
+{
+	extern unsigned char seq_nt4_table[256];
+	int i, reg;
+	uint8_t *qseq0[2];
+
+	qseq0[0] = (uint8_t*)kmalloc(km, qlen);
+	qseq0[1] = (uint8_t*)kmalloc(km, qlen);
+	for (i = 0; i < qlen; ++i) {
+		qseq0[0][i] = seq_nt4_table[(uint8_t)qstr[i]];
+		qseq0[1][qlen - 1 - i] = qseq0[0][i] < 4? 3 - qseq0[0][i] : 4;
+	}
+
+	for (reg = 0; reg < n_regs; ++reg) {
+		mm_reg1_t *r = &regs[reg];
+		int32_t rid = a[r->as].x<<1>>33, rev = a[r->as].x>>63;
+		uint8_t *tseq;
+		tseq = (uint8_t*)kmalloc(km, r->re - r->rs);
+		for (i = 0; i < r->cnt - 1; ++i) {
+			uint8_t *qseq;
+			int32_t rs, re, qs, qe, ret;
+			rs = (int32_t)a[r->as + i].x + 1;
+			re = (int32_t)a[r->as + i + 1].x + 1;
+			qs = (int32_t)a[r->as + i].y + 1;
+			qe = (int32_t)a[r->as + i + 1].y + 1;
+			qseq = &qseq0[rev][qs];
+			ret = mm_idx_getseq(mi, rid, rs, re, tseq);
+			assert(ret > 0);
+		}
+		kfree(km, tseq);
+	}
+
+	kfree(km, qseq0[0]); kfree(km, qseq0[1]);
+}
diff --git a/index.c b/index.c
index e89c2f2..6a97718 100644
--- a/index.c
+++ b/index.c
@@ -82,6 +82,18 @@ void mm_idx_stat(const mm_idx_t *mi)
 			__func__, realtime() - mm_realtime0, cputime() / (realtime() - mm_realtime0), n, 100.0*n1/n, (double)sum / n, (double)len / sum);
 }
 
+int mm_idx_getseq(const mm_idx_t *mi, uint32_t rid, uint32_t st, uint32_t en, uint8_t *seq)
+{
+	uint64_t i, st1, en1;
+	if (rid >= mi->n_seq || st >= mi->seq[rid].len) return -1;
+	if (en > mi->seq[rid].len) en = mi->seq[rid].len;
+	st1 = mi->seq[rid].offset + st;
+	en1 = mi->seq[rid].offset + en;
+	for (i = st1; i < en1; ++i)
+		seq[i - st1] = mm_seq4_get(mi->S, i);
+	return en - st;
+}
+
 uint32_t mm_idx_cal_max_occ(const mm_idx_t *mi, float f)
 {
 	int i;
diff --git a/map.c b/map.c
index 930bd86..95e652d 100644
--- a/map.c
+++ b/map.c
@@ -11,7 +11,6 @@
 void mm_mapopt_init(mm_mapopt_t *opt)
 {
 	memset(opt, 0, sizeof(mm_mapopt_t));
-	opt->n_frag_mini = 100000;
 	opt->max_occ_frac = 1e-5f;
 	opt->mid_occ_frac = 2e-4f;
 	opt->sdust_thres = 0;
@@ -176,6 +175,7 @@ mm_reg1_t *mm_gen_reg(int qlen, int n_u, uint64_t *u, mm128_t *a)
 			ri->qs = qlen - ((int32_t)a[k + ri->cnt - 1].y + 1);
 			ri->qe = qlen - ((int32_t)a[k].y + 1 - (int32_t)(a[k].y>>32));
 		}
+		ri->as = k;
 		k += ri->cnt;
 	}
 	return r;
@@ -224,13 +224,13 @@ void mm_select_sub(float mask_level, float pri_ratio, int *n_, mm_reg1_t *r, voi
 	}
 }
 
-mm_reg1_t *mm_map_frag(const mm_mapopt_t *opt, const mm_idx_t *mi, mm_tbuf_t *b, uint32_t m_st, uint32_t m_en, const char *qname, int qlen, int *n_regs)
+mm_reg1_t *mm_map_frag(const mm_mapopt_t *opt, const mm_idx_t *mi, mm_tbuf_t *b, uint32_t m_st, uint32_t m_en, const char *qname, int qlen, const char *seq, int *n_regs)
 {
 	int i, n = m_en - m_st, j, n_a, n_u;
 	uint64_t *u;
 	mm_match_t *m;
 	mm128_t *a;
-	mm_reg1_t *reg;
+	mm_reg1_t *regs;
 
 	// convert to local representation
 	m = (mm_match_t*)kmalloc(b->km, n * sizeof(mm_match_t));
@@ -294,13 +294,15 @@ mm_reg1_t *mm_map_frag(const mm_mapopt_t *opt, const mm_idx_t *mi, mm_tbuf_t *b,
 	//for (i = 0; i < n_a; ++i) printf("%c\t%s\t%d\t%d\n", "+-"[a[i].x>>63], mi->seq[a[i].x<<1>>33].name, (uint32_t)a[i].x, (uint32_t)a[i].y);
 
 	n_u = mm_chain_dp(opt->max_gap, opt->bw, opt->max_skip, opt->min_score, n_a, a, &u, b->km);
-	reg = mm_gen_reg(qlen, n_u, u, a);
+	regs = mm_gen_reg(qlen, n_u, u, a);
 	*n_regs = n_u;
+	mm_select_sub(opt->mask_level, opt->pri_ratio, n_regs, regs, b->km);
+	mm_align_skeleton(b->km, opt, mi, qlen, seq, *n_regs, regs, a);
 
 	// free
 	kfree(b->km, a);
 	kfree(b->km, u);
-	return reg;
+	return regs;
 }
 
 mm_reg1_t *mm_map(const mm_idx_t *mi, int l_seq, const char *seq, int *n_regs, mm_tbuf_t *b, const mm_mapopt_t *opt, const char *qname)
@@ -310,8 +312,8 @@ mm_reg1_t *mm_map(const mm_idx_t *mi, int l_seq, const char *seq, int *n_regs, m
 	mm_sketch(b->km, seq, l_seq, mi->w, mi->k, 0, mi->is_hpc, &b->mini);
 	if (opt->sdust_thres > 0)
 		mm_dust_minier(&b->mini, l_seq, seq, opt->sdust_thres, b->sdb);
-	regs = mm_map_frag(opt, mi, b, 0, b->mini.n, qname, l_seq, n_regs);
-	mm_select_sub(opt->mask_level, opt->pri_ratio, n_regs, regs, b->km);
+	regs = mm_map_frag(opt, mi, b, 0, b->mini.n, qname, l_seq, seq, n_regs);
+//	mm_select_sub(opt->mask_level, opt->pri_ratio, n_regs, regs, b->km);
 	return regs;
 }
 
diff --git a/minimap.h b/minimap.h
index 96df02c..d886f8c 100644
--- a/minimap.h
+++ b/minimap.h
@@ -29,7 +29,7 @@ typedef struct {
 
 typedef struct {
 	char *name;      // name of the db sequence
-	uint64_t offset; // offset in mm_idx_t::seq16
+	uint64_t offset; // offset in mm_idx_t::S
 	uint32_t len;    // length
 } mm_idx_seq_t;
 
@@ -47,10 +47,10 @@ typedef struct {
 	int32_t score;
 	int32_t qs, qe, rs, re;
 	int32_t parent, subsc;
+	int32_t as;
 } mm_reg1_t;
 
 typedef struct {
-	int n_frag_mini;
 	float max_occ_frac;
 	float mid_occ_frac;
 	int sdust_thres;  // score threshold for SDUST; 0 to disable
@@ -91,6 +91,7 @@ mm_idx_t *mm_idx_gen(struct bseq_file_s *fp, int w, int k, int b, int is_hpc, in
 uint32_t mm_idx_cal_max_occ(const mm_idx_t *mi, float f);
 void mm_idx_stat(const mm_idx_t *idx);
 const uint64_t *mm_idx_get(const mm_idx_t *mi, uint64_t minier, int *n);
+int mm_idx_getseq(const mm_idx_t *mi, uint32_t rid, uint32_t st, uint32_t en, uint8_t *seq);
 
 mm_idx_t *mm_idx_build(const char *fn, int w, int k, int is_hpc, int n_threads);
 
diff --git a/mmpriv.h b/mmpriv.h
index 82684b3..66d8187 100644
--- a/mmpriv.h
+++ b/mmpriv.h
@@ -16,6 +16,8 @@ uint32_t ks_ksmall_uint32_t(size_t n, uint32_t arr[], size_t kk);
 
 int mm_chain_dp(int max_dist, int bw, int max_skip, int min_sc, int n, mm128_t *a, uint64_t **_u, void *km);
 
+void mm_align_skeleton(void *km, const mm_mapopt_t *opt, const mm_idx_t *mi, int qlen, const char *qstr, int n_regs, mm_reg1_t *regs, mm128_t *a);
+
 #ifdef __cplusplus
 }
 #endif