diff --git a/README b/README
index 82a0d7ae0ee29387b1c01fd7b4503eae105ffa4d..56393949df878989654ad8224ce536cc88115a9f 100644
--- a/README
+++ b/README
@@ -61,6 +61,8 @@ If increment is not specified, it defaults to 1.
 
 1 line by SV type, like above.
 
+IMPORTANT: only deletion is implemented yet.
+
 We use SVsim to generate positions of SVs. https://github.com/GregoryFaust/SVsim
 
 
diff --git a/build_pop.py b/build_pop.py
index b3b2f1ad51174b703e40f6096ed4973a311105fe..164daf58dfb719403bd651b544bb4f39fac81dae 100755
--- a/build_pop.py
+++ b/build_pop.py
@@ -14,6 +14,8 @@ parser.add_argument("--sv-list", help="File containing the SVs", required=True)
 parser.add_argument("--coverage", help="Coverage of reads (default: 15)", default=15, type=int)
 parser.add_argument("--output-directory", help="Output directory (default: res)", default="res")
 parser.add_argument("--tmp-directory", help="Temporary directory (default: tmp)", default="tmp")
+parser.add_argument("--force-polymorphism", help="Force polymorphism for each SV", action='store_const', const=True,
+                    default=False)
 
 args = parser.parse_args()
 
@@ -31,9 +33,33 @@ if not os.path.isfile(reference + ".fai"):
     os.system("samtools faidx " + reference)
 
 
+#############
+# FUNCTIONS #
+#############
+
+
 def allele(frequency):
     return 1 if random.uniform(0, 1) < frequency else 0
 
+
+def get_genotypes_for_inds():
+    all_genotypes = []
+    genotypes_row = []
+    for i in range(1, nb_inds + 1):
+        genotype = str(allele(freq)) + "/" + str(allele(freq))
+        genotype_data = vcf.model._Call(None, "INDIV_" + str(i), vcf.model.make_calldata_tuple("GT")(GT=genotype))
+        genotypes_row.append(genotype_data)
+        all_genotypes.append(genotype)
+    return all_genotypes, genotypes_row
+
+
+def svsort(sv, chr):
+    """
+    Function to sort regions
+    """
+    return int(genotypes_for_inds[chr][sv]["start"])
+
+
 prg_path = os.path.dirname(os.path.realpath(__file__))
 
 if not os.path.isdir(tmp_dir):
@@ -93,22 +119,16 @@ with open(os.path.join(tmp_dir, "reference-sv.bed"), "r") as bed:
         if parts[0] not in genotypes_for_inds:
             genotypes_for_inds[parts[0]] = {}
         genotypes_for_inds[parts[0]][parts[3]] = {"start": int(parts[1]), "end": int(parts[2]), "genotypes": []}
-        genotypes = []
-        polymorph = False
-        while not polymorph:
-            unique_genotypes = set()
-            all_genotypes = []
-            genotypes_tmp = []
-            for i in range(1, nb_inds+1):
-                genotype = str(allele(freq)) + "/" + str(allele(freq))
-                genotype_data = vcf.model._Call(None, "INDIV_" + str(i), vcf.model.make_calldata_tuple("GT")(GT=genotype))
-                genotypes_tmp.append(genotype_data)
-                unique_genotypes.add(genotype)
-                all_genotypes.append(genotype)
-            polymorph = len(unique_genotypes) > 1
-            if polymorph:
-                genotypes += genotypes_tmp
-                genotypes_for_inds[parts[0]][parts[3]]["genotypes"] = [x.split("/") for x in all_genotypes]
+
+        # Get genotypes:
+        if args.force_polymorphism:
+            polymorph = False
+            while not polymorph:
+                all_genotypes, genotypes = get_genotypes_for_inds()
+                polymorph = len(set(all_genotypes)) > 1
+        else:
+            all_genotypes, genotypes = get_genotypes_for_inds()
+        genotypes_for_inds[parts[0]][parts[3]]["genotypes"] = [x.split("/") for x in all_genotypes]
 
         info = {"END": int(parts[2]), "AF": freq}
         vcf_record = vcf.model._Record(parts[0], int(parts[1]), parts[3], "N", [vcf.model._SV("DEL")], ".", ".", info, "GT", [0], genotypes)
@@ -123,13 +143,6 @@ with open(os.path.join(tmp_dir, "reference-sv.bed"), "r") as bed:
 print("BUILD FASTA GENOME FOR EACH INDIVIDUAL...\n")
 
 
-def svsort(sv, chr):
-    """
-    Function to sort regions
-    """
-    return int(genotypes_for_inds[chr][sv]["start"])
-
-
 fasta_orig = SeqIO.index(reference, "fasta")
 
 for chr, svs_infos in genotypes_for_inds.items():