diff --git a/clipkit/msa.py b/clipkit/msa.py
index a72beec..c1a2559 100644
--- a/clipkit/msa.py
+++ b/clipkit/msa.py
@@ -102,12 +102,20 @@ def is_any_entry_sequence_only_gaps(self) -> tuple[bool, Union[str, None]]:
 
     def trim(
         self,
-        mode: TrimmingMode,
+        mode: TrimmingMode=TrimmingMode.smart_gap,
         gap_threshold=None,
+        site_positions_to_trim=None,
     ) -> np.array:
-        self._site_positions_to_trim = self.determine_site_positions_to_trim(
-            mode, gap_threshold
-        )
+        if site_positions_to_trim is not None:
+            if isinstance(site_positions_to_trim, list):
+                site_positions_to_trim = np.array(site_positions_to_trim)
+            if not isinstance(site_positions_to_trim, np.ndarray):
+                raise ValueError("site_positions_to_trim must be a list or np array")
+            self._site_positions_to_trim = site_positions_to_trim
+        else:
+            self._site_positions_to_trim = self.determine_site_positions_to_trim(
+                mode, gap_threshold
+            )
         self._site_positions_to_keep = np.delete(
             np.arange(self._original_length), self._site_positions_to_trim
         )
diff --git a/clipkit/version.py b/clipkit/version.py
index 9aa3f90..58039f5 100644
--- a/clipkit/version.py
+++ b/clipkit/version.py
@@ -1 +1 @@
-__version__ = "2.1.0"
+__version__ = "2.1.1"
diff --git a/tests/unit/test_msa.py b/tests/unit/test_msa.py
new file mode 100644
index 0000000..7649c93
--- /dev/null
+++ b/tests/unit/test_msa.py
@@ -0,0 +1,51 @@
+import pytest
+import numpy as np
+
+from Bio import AlignIO
+from clipkit.msa import MSA
+
+def get_biopython_msa(file_path, file_format="fasta"):
+    return AlignIO.read(open(file_path), file_format)
+
+
+class TestMSA(object):
+    def test_clipkit_msa_from_bio_msa(self):
+        bio_msa = get_biopython_msa("tests/unit/examples/simple.fa")
+        msa = MSA.from_bio_msa(bio_msa)
+        assert msa.header_info == [{'id': '1', 'name': '1', 'description': '1'}, {'id': '2', 'name': '2', 'description': '2'}, {'id': '3', 'name': '3', 'description': '3'}, {'id': '4', 'name': '4', 'description': '4'}, {'id': '5', 'name': '5', 'description': '5'}]
+        expected_seq_records = np.array([
+            ['A', '-', 'G', 'T', 'A', 'T'],
+            ['A', '-', 'G', '-', 'A', 'T'],
+            ['A', '-', 'G', '-', 'T', 'A'],
+            ['A', 'G', 'A', '-', 'T', 'A'],
+            ['A', 'C', 'a', '-', 'T', '-']
+        ])
+        np.testing.assert_equal(msa.seq_records, expected_seq_records)
+
+    def test_trim_by_provided_site_positions_np_array(self):
+        bio_msa = get_biopython_msa("tests/unit/examples/simple.fa")
+        msa = MSA.from_bio_msa(bio_msa)
+        sites_to_trim = np.array([1, 4])
+        msa.trim(site_positions_to_trim=sites_to_trim)
+        expected_sites_kept = np.array([
+            ['A', 'G', 'T', 'T'],
+            ['A', 'G', '-', 'T'],
+            ['A', 'G', '-', 'A'],
+            ['A', 'A', '-', 'A'],
+            ['A', 'a', '-', '-']
+        ])
+        np.testing.assert_equal(msa.sites_kept, expected_sites_kept)
+
+    def test_trim_by_provided_site_positions_list(self):
+        bio_msa = get_biopython_msa("tests/unit/examples/simple.fa")
+        msa = MSA.from_bio_msa(bio_msa)
+        sites_to_trim = [1, 4]
+        msa.trim(site_positions_to_trim=sites_to_trim)
+        expected_sites_kept = np.array([
+            ['A', 'G', 'T', 'T'],
+            ['A', 'G', '-', 'T'],
+            ['A', 'G', '-', 'A'],
+            ['A', 'A', '-', 'A'],
+            ['A', 'a', '-', '-']
+        ])
+        np.testing.assert_equal(msa.sites_kept, expected_sites_kept)