Genetic distance calculation#

Fast pairwise distance estimation#

For a limited number of evolutionary models a fast implementation is available.

from cogent3 import available_distances

available_distances()
Specify a pairwise genetic distance calculator using 'Abbreviation' (case insensitive).
AbbreviationSuitable for moltype
paralineardna, rna, protein
logdetdna, rna, protein
jc69dna, rna
tn93dna, rna
hammingdna, rna, protein, text, bytes
pdistdna, rna, protein, text, bytes

6 rows x 2 columns

Computing genetic distances using the Alignment object#

Abbreviations listed from available_distances() can be used as values for the distance_matrix(calc=<abbreviation>).

from cogent3 import load_aligned_seqs

aln = load_aligned_seqs("data/primate_brca1.fasta", moltype="dna")
dists = aln.distance_matrix(calc="tn93", show_progress=False)
dists
namesChimpanzeeGalagoGorillaHowlerMonHumanOrangutanRhesus
Chimpanzee0.00000.19210.00540.07040.00890.01400.0396
Galago0.19210.00000.19230.21570.19650.19440.1962
Gorilla0.00540.19230.00000.07000.00860.01370.0393
HowlerMon0.07040.21570.07000.00000.07360.07190.0736
Human0.00890.19650.00860.07360.00000.01730.0423
Orangutan0.01400.19440.01370.07190.01730.00000.0411
Rhesus0.03960.19620.03930.07360.04230.04110.0000

Using the distance calculator directly#

from cogent3 import get_distance_calculator, load_aligned_seqs

aln = load_aligned_seqs("data/primate_brca1.fasta")
dist_calc = get_distance_calculator("tn93", alignment=aln)
dist_calc
<cogent3.evolve.fast_distance.TN93Pair at 0x7f15bca39700>
dist_calc.run(show_progress=False)
dists = dist_calc.get_pairwise_distances()
dists
namesChimpanzeeGalagoGorillaHowlerMonHumanOrangutanRhesus
Chimpanzee0.00000.19210.00540.07040.00890.01400.0396
Galago0.19210.00000.19230.21570.19650.19440.1962
Gorilla0.00540.19230.00000.07000.00860.01370.0393
HowlerMon0.07040.21570.07000.00000.07360.07190.0736
Human0.00890.19650.00860.07360.00000.01730.0423
Orangutan0.01400.19440.01370.07190.01730.00000.0411
Rhesus0.03960.19620.03930.07360.04230.04110.0000

The distance calculation object can provide more information. For instance, the standard errors.

dist_calc.stderr
Standard Error of Pairwise Distances
Seq1 \ Seq2GalagoHowlerMonRhesusOrangutanGorillaHumanChimpanzee
Galago00.0102748270583958960.0096163078326485620.0095356465322767870.0094913822495401760.0096150330918649170.009469268026590141
HowlerMon0.01027482705839589600.0054118117125547720.00533485849516111750.0052656124746942460.0054067602387489840.005273572620183854
Rhesus0.0096163078326485620.00541181171255477200.00394085494178657550.0038527981619030950.0040050459201001250.0038665597157698894
Orangutan0.0095356465322767870.00533485849516111750.003940854941786575500.00222911247430113750.00251518387918036550.0022606571679022955
Gorilla0.0094913822495401760.0052656124746942460.0038527981619030950.002229112474301137500.00175969199023268760.0013848543487237903
Human0.0096150330918649170.0054067602387489840.0040050459201001250.00251518387918036550.001759691990232687600.0017949285088691988
Chimpanzee0.0094692680265901410.0052735726201838540.00386655971576988940.00226065716790229550.00138485434872379030.00179492850886919880

7 rows x 8 columns

Likelihood based pairwise distance estimation#

The standard cogent3 likelihood function can also be used to estimate distances. Because these require numerical optimisation they can be significantly slower than the fast estimation approach above.

The following will use the F81 nucleotide substitution model and perform numerical optimisation.

from cogent3 import get_model, load_aligned_seqs
from cogent3.evolve import distance

aln = load_aligned_seqs("data/primate_brca1.fasta", moltype="dna")
d = distance.EstimateDistances(aln, submodel=get_model("F81"))
d.run(show_progress=False)
dists = d.get_pairwise_distances()
dists
namesChimpanzeeGalagoGorillaHowlerMonHumanOrangutanRhesus
Chimpanzee0.00000.18920.00540.06970.00890.01400.0395
Galago0.18920.00000.18910.21120.19340.19150.1930
Gorilla0.00540.18910.00000.06930.00860.01360.0391
HowlerMon0.06970.21120.06930.00000.07290.07130.0729
Human0.00890.19340.00860.07290.00000.01730.0421
Orangutan0.01400.19150.01360.07130.01730.00000.0410
Rhesus0.03950.19300.03910.07290.04210.04100.0000

Get the names of sequences with max pairwise distance#

Given a DistanceMatrix object, finding the sequences that have the maximum pairwise distance is achieved through the max_pair method.

from cogent3 import load_aligned_seqs

aln = load_aligned_seqs("data/primate_brca1.fasta", moltype="dna")
dists = aln.distance_matrix(calc="tn93", show_progress=False)
dists.max_pair()
('Galago', 'HowlerMon')

To find the maximum distance, index the DistanceMatrix with the result of max_pair.

dists[dists.max_pair()]
0.2156879978632928

Get the names of sequences with min pairwise distance#

Given a DistanceMatrix object, finding the sequences that have the minimum pairwise distance is achieved through the min_pair method.

Note

As the distance between a sequence and itself is zero, and this is not informative, min_pair will return the smallest distance not on the diagonal.

from cogent3 import load_aligned_seqs

aln = load_aligned_seqs("data/primate_brca1.fasta", moltype="dna")
dists = aln.distance_matrix(calc="tn93", show_progress=False)
dists.min_pair()
('Chimpanzee', 'Gorilla')

To find the minimum distance, index the DistanceMatrix with the result of min_pair.

dists[dists.min_pair()]
0.005354100636467117