def test_swapping(gap_penalty, local, seed):
"""
Check if `align_banded()` returns a 'swapped' alignment, if
the order of input sequences is swapped.
"""
np.random.seed(seed)
band = (
np.random.randint(-30, -10),
np.random.randint( 10, 30)
)
seq1, seq2 = _create_random_pair(seed)
matrix = align.SubstitutionMatrix.std_protein_matrix()
ref_alignments = align.align_banded(
seq1, seq2, matrix, band=band, local=local, gap_penalty=gap_penalty
)
test_alignments = align.align_banded(
seq2, seq1, matrix, band=band, local=local, gap_penalty=gap_penalty
)
if len(ref_alignments) != 1 or len(test_alignments) != 1:
# If multiple optimal alignments exist,
# it is not easy to assign a swapped one to an original one
# therefore, simply return in this case
# the number of tested seeds should be large enough to generate
# a reasonable number of suitable test cases
return
ref_alignment = ref_alignments[0]
test_alignment = test_alignments[0]
assert test_alignment.sequences[0] == ref_alignment.sequences[1]
assert test_alignment.sequences[1] == ref_alignment.sequences[0]
assert np.array_equal(test_alignment.trace, ref_alignment.trace[:, ::-1])
def test_simple_alignment(gap_penalty, local, band_width):
"""
Test `align_banded()` by comparing the output to `align_optimal()`.
This test uses a pair of highly similar short sequences.
"""
# Cyclotide C, Uniprot: P86843
seq1 = seq.ProteinSequence("gvpcaescvwipctvtallgcsckdkvcyld")
# Cyclotide F, Uniprot: P86846
seq2 = seq.ProteinSequence("gipcgescvfipcissvvgcsckskvcyld")
matrix = align.SubstitutionMatrix.std_protein_matrix()
ref_alignments = align.align_optimal(
seq1, seq2, matrix,
gap_penalty=gap_penalty, local=local, terminal_penalty=False
)
# Remove terminal gaps in reference to obtain a true semi-global
# alignment, as returned by align_banded()
ref_alignments = [align.remove_terminal_gaps(al) for al in ref_alignments]
test_alignments = align.align_banded(
seq1, seq2, matrix, (-band_width, band_width),
gap_penalty=gap_penalty, local=local
)
assert len(test_alignments) == len(ref_alignments)
for alignment in test_alignments:
assert alignment in ref_alignments
def map_sequence(read, diag):
deviation = int(3 * np.sqrt(len(read) * P_INDEL))
if diag is None:
return None
else:
return align.align_banded(
read, orig_genome, matrix, gap_penalty=-10,
band = (diag - deviation, diag + deviation),
max_number = 1
)[0]
def test_complex_alignment(sequences, gap_penalty, local, seq_indices):
"""
Test `align_banded()` by comparing the output to `align_optimal()`.
This test uses a set of long sequences, which are pairwise compared.
The band should be chosen sufficiently large so `align_banded()`
can return the optimal alignment(s).
"""
MAX_NUMBER = 100
matrix = align.SubstitutionMatrix.std_protein_matrix()
index1, index2 = seq_indices
seq1 = sequences[index1]
seq2 = sequences[index2]
ref_alignments = align.align_optimal(
seq1, seq2, matrix,
gap_penalty=gap_penalty, local=local, terminal_penalty=False,
max_number=MAX_NUMBER
)
# Remove terminal gaps in reference to obtain a true semi-global
# alignment, as returned by align_banded()
ref_alignments = [align.remove_terminal_gaps(al) for al in ref_alignments]
identity = align.get_sequence_identity(ref_alignments[0])
# Use a relatively small band width, if the sequences are similar,
# otherwise use the entire search space
band_width = 100 if identity > 0.5 else len(seq1) + len(seq2)
test_alignments = align.align_banded(
seq1, seq2, matrix, (-band_width, band_width),
gap_penalty=gap_penalty, local=local, max_number=MAX_NUMBER
)
try:
assert test_alignments[0].score == ref_alignments[0].score
if len(ref_alignments) < MAX_NUMBER:
# Only test if the exact same alignments were created,
# if the number of traces was not limited by MAX_NUMBER
assert len(test_alignments) == len(ref_alignments)
for alignment in test_alignments:
assert alignment in ref_alignments
except AssertionError:
print("First tested alignment:")
print()
print(test_alignments[0])
print("\n")
print("First reference alignment:")
print()
print(ref_alignments[0])
raise
def test_large_sequence_mapping(length, excerpt_length, seed):
"""
Test whether an excerpt of a very large sequence is aligned to that
sequence at the position, where the excerpt was taken from.
"""
BAND_WIDTH = 100
np.random.seed(seed)
sequence = seq.NucleotideSequence()
sequence.code = np.random.randint(len(sequence.alphabet), size=length)
excerpt_pos = np.random.randint(len(sequence) - excerpt_length)
excerpt = sequence[excerpt_pos : excerpt_pos + excerpt_length]
diagonal = np.random.randint(
excerpt_pos - BAND_WIDTH,
excerpt_pos + BAND_WIDTH
)
band = (
diagonal - BAND_WIDTH,
diagonal + BAND_WIDTH
)
print(band)
print(len(sequence), len(excerpt))
matrix = align.SubstitutionMatrix.std_nucleotide_matrix()
test_alignments = align.align_banded(
excerpt, sequence, matrix, band=band
)
# The excerpt should be uniquely mappable to a single location on
# the long sequence
assert len(test_alignments) == 1
test_alignment = test_alignments[0]
test_trace = test_alignment.trace
ref_trace = np.stack([
np.arange(len(excerpt)),
np.arange(excerpt_pos, len(excerpt) + excerpt_pos)
], axis=1)
assert np.array_equal(test_trace, ref_trace)
# Now we would like to have a closer look on the difference between the
# original and the B.1.1.7 genome.
#
# Mutations in the B.1.1.7 variant
# --------------------------------
#
# To get an rough overview about the overall sequence identity between
# the genomes and the locations of mutations in the B.1.1.7 variant,
# we need to align the original genome to our assembled one.
# As both genomes are expected to be highly similar, we can use a banded
# alignment again using a very conservative band width.
BAND_WIDTH = 1000
genome_alignment = align.align_banded(
var_genome, orig_genome, matrix,
band=(-BAND_WIDTH//2, BAND_WIDTH//2), max_number=1
)[0]
identity = align.get_sequence_identity(genome_alignment, 'all')
print(f"Sequence identity: {identity * 100:.2f} %")
########################################################################
# Now we would like to have a closer look at the mutation locations.
# To contextualize the locations we plot the mutation frequency along
# with the gene locations.
# The genomic coordinates for each gene can be extracted from the
# already downloaded *GenBank* file of the reference genome.
N_BINS = 50
# Get genomic coordinates for all SARS-Cov-2 genes
gb_file = gb.GenBankFile.read(orig_genome_file)
# aligned to each other, if :math:`D_L \leq j - i \leq D_U`.
#
# In our case we center the diagonal band to the diagonal of the match
# and use a fixed band width :math:`W = D_U - D_L`.
BAND_WIDTH = 4
matrix = SubstitutionMatrix.std_protein_matrix()
alignments = []
for query_pos, ref_pos in matches:
diagonal = ref_pos - query_pos
alignment = align.align_banded(
query,
reference,
matrix,
gap_penalty=-5,
max_number=1,
# Center the band at the match diagonal and extend the band by
# one half of the band width in each direction
band=(diagonal - BAND_WIDTH // 2, diagonal + BAND_WIDTH // 2))[0]
alignments.append(alignment)
for alignment in alignments:
print(alignment)
print("\n")
########################################################################
# 4. Significance evaluation
# """"""""""""""""""""""""""
# We have obtained two alignments, but which one of them is the
# 'correct' one?
# The diagonal of this match can be seen in the figure:
# It is the almost continuous line on the right side.
#
# For the gapped alignment we use :func:`align_banded()`, which reduces
# the alignment search space to a narrow diagonal band.
BAND_WIDTH = 1000
alignments = []
matrix = align.SubstitutionMatrix.std_nucleotide_matrix()
for strand, m1_pos, genome_pos in trigger_matches:
genome = genomic_seqs[strand]
diagonal = genome_pos - m1_pos
alignment = align.align_banded(m1_sequence,
genome,
matrix,
band=(diagonal - BAND_WIDTH,
diagonal + BAND_WIDTH),
max_number=1)[0]
alignments.append((strand, alignment))
strand, best_alignment = max(alignments,
key=lambda strand_alignment: alignment[1].score)
########################################################################
# For visualization purposes we have to apply a renumbering function
# for the genomic sequence,
# since the indices in the alignment trace refer to the reverse
# complement sequence, but we want the numbers to refer to the original
# genomic sequence.
# Reverse sequence numbering for second sequence (genome) in alignment