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Calculate Depth of Coverage and Breadth of Coverage from a bam file. This function calculates by chromsome and for the entire genome. Additionally, if the mtchr (Mitochondrial chromosome name) is provided, nuclear coverage and the ratio of mtDNA:nuclear DNA is calculated. #bam #stats
#
# This script calculates the depth of coverage and breadth of coverage for a given bam.
# Outputs a dictionary containing the contig/chromosome names and the depth and breadth of coverage for each
# and for the entire genome.
#
# If you optionally specify the name of the mitochondrial chromosome (e.g. mtDNA, chrM, chrMT)
# The script will also generate breadth and depth of coverage for the nuclear genome AND the ratio
# of mtDNA:nuclearDNA; which can act as a proxy in some cases for mitochondrial count within an individual.
#
# Author: Daniel E. Cook
# Website: Danielecook.com
#
import os
import re
from subprocess import Popen, PIPE
def get_contigs(bam):
header, err = Popen(["samtools","view","-H",bam], stdout=PIPE, stderr=PIPE).communicate()
if err != "":
raise Exception(err)
# Extract contigs from header and convert contigs to integers
contigs = {}
for x in re.findall("@SQ\WSN:(?P<chrom>[A-Za-z0-9_]*)\WLN:(?P<length>[0-9]+)", header):
contigs[x[0]] = int(x[1])
return contigs
def coverage(bam, mtchr = None):
# Check to see if file exists
if os.path.isfile(bam) == False:
raise Exception("Bam file does not exist")
contigs = get_contigs(bam)
# Guess mitochondrial chromosome
mtchr = [x for x in contigs if x.lower().find("m") == 0]
if len(mtchr) != 1:
mtchr = None
else:
mtchr = mtchr[0]
coverage_dict = {}
for c in contigs.keys():
command = "samtools depth -r %s %s | awk '{sum+=$3;cnt++}END{print cnt \"\t\" sum}'" % (c, bam)
coverage_dict[c] = {}
coverage_dict[c]["Bases Mapped"], coverage_dict[c]["Sum of Depths"] = map(int,Popen(command, stdout=PIPE, shell = True).communicate()[0].strip().split("\t"))
coverage_dict[c]["Breadth of Coverage"] = coverage_dict[c]["Bases Mapped"] / float(contigs[c])
coverage_dict[c]["Depth of Coverage"] = coverage_dict[c]["Sum of Depths"] / float(contigs[c])
coverage_dict[c]["Length"] = int(contigs[c])
# Calculate Genome Wide Breadth of Coverage and Depth of Coverage
genome_length = float(sum(contigs.values()))
coverage_dict["genome"] = {}
coverage_dict["genome"]["Length"] = int(genome_length)
coverage_dict["genome"]["Bases Mapped"] = sum([x["Bases Mapped"] for k, x in coverage_dict.iteritems() if k != "genome"])
coverage_dict["genome"]["Sum of Depths"] = sum([x["Sum of Depths"] for k, x in coverage_dict.iteritems() if k != "genome"])
coverage_dict["genome"]["Breadth of Coverage"] = sum([x["Bases Mapped"] for k, x in coverage_dict.iteritems() if k != "genome"]) / float(genome_length)
coverage_dict["genome"]["Depth of Coverage"] = sum([x["Sum of Depths"] for k, x in coverage_dict.iteritems() if k != "genome"]) / float(genome_length)
if mtchr != None:
# Calculate nuclear breadth of coverage and depth of coverage
ignore_contigs = [mtchr, "genome", "nuclear"]
coverage_dict["nuclear"] = {}
coverage_dict["nuclear"]["Length"] = sum([x["Length"] for k,x in coverage_dict.iteritems() if k not in ignore_contigs ])
coverage_dict["nuclear"]["Bases Mapped"] = sum([x["Bases Mapped"] for k, x in coverage_dict.iteritems() if k not in ignore_contigs])
coverage_dict["nuclear"]["Sum of Depths"] = sum([x["Sum of Depths"] for k, x in coverage_dict.iteritems() if k not in ignore_contigs])
coverage_dict["nuclear"]["Breadth of Coverage"] = sum([x["Bases Mapped"] for k, x in coverage_dict.iteritems() if k not in ignore_contigs]) / float(coverage_dict["nuclear"]["Length"])
coverage_dict["nuclear"]["Depth of Coverage"] = sum([x["Sum of Depths"] for k, x in coverage_dict.iteritems() if k not in ignore_contigs]) / float(coverage_dict["nuclear"]["Length"])
# Calculate the ratio of mtDNA depth to nuclear depth
coverage_dict["genome"]["mt_ratio"] = coverage_dict[mtchr]["Depth of Coverage"] / float(coverage_dict["nuclear"]["Depth of Coverage"])
# Flatten Dictionary
coverage = []
for k,v in coverage_dict.items():
for x in v.items():
coverage += [(k,x[0], x[1])]
return coverage

What is syntac to run this script?

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