# HG changeset patch # User nikhil-joshi # Date 1426034320 14400 # Node ID c7ea7b299f01692e21480d05afe3ffb0bc3f5cab # Parent 0a70eb1e643287ad12bac08fd412b7a85f48b771 Uploaded diff -r 0a70eb1e6432 -r c7ea7b299f01 scythe.xml --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/scythe.xml Tue Mar 10 20:38:40 2015 -0400 @@ -0,0 +1,80 @@ + + Trimming adapters/contaminants using a Naive Bayesian classifier + + + scythe -a $adapter_file + + #if $input_fastq.ext == "fastq": + -q sanger + #else if $input_fastq.ext == "fastqsanger": + -q sanger + #else if $input_fastq.ext == "fastqillumina": + -q illumina + #else if $input_fastq.ext == "fastqsolexa": + -q solexa + #end if + + #if str($add_tag) == "add_tag_true": + -t + #end if + + #if str($prior) != "": + -p $prior + #end if + + #if str($min_match) != "": + -n $min_match + #end if + + #if str($min_keep) != "": + -M $min_keep + #end if + + #if str($matches_file) == "matches_file_true": + -m $output_matches + #end if + + -o $output_trimmed $input_fastq 2>&1 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + (matches_file == True) + + + + +Scythe uses a Naive Bayesian approach to classify contaminant substrings in sequence reads. It considers quality information, which can make it robust in picking out 3'-end adapters, which often include poor quality bases. + +Most next generation sequencing reads have deteriorating quality towards the 3'-end. It's common for a quality-based trimmer to be employed before mapping, assemblies, and analysis to remove these poor quality bases. However, quality-based trimming could remove bases that are helpful in identifying (and removing) 3'-end adapter contaminants. Thus, it is recommended you run Scythe before quality-based trimming, as part of a read quality control pipeline. + +The Bayesian approach Scythe uses compares two likelihood models: the probability of seeing the matches in a sequence given contamination, and not given contamination. Given that the read is contaminated, the probability of seeing a certain number of matches and mistmatches is a function of the quality of the sequence. Given the read is not contaminated (and is thus assumed to be random sequence), the probability of seeing a certain number of matches and mismatches is chance. The posterior is calculated across both these likelihood models, and the class (contaminated or not contaminated) with the maximum posterior probability is the class selected. + +Scythe will infer the quality type from the datatype of the file. + + + diff -r 0a70eb1e6432 -r c7ea7b299f01 scythe/scythe.xml --- a/scythe/scythe.xml Tue Mar 10 20:37:06 2015 -0400 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,80 +0,0 @@ - - Trimming adapters/contaminants using a Naive Bayesian classifier - - - scythe -a $adapter_file - - #if $input_fastq.ext == "fastq": - -q sanger - #else if $input_fastq.ext == "fastqsanger": - -q sanger - #else if $input_fastq.ext == "fastqillumina": - -q illumina - #else if $input_fastq.ext == "fastqsolexa": - -q solexa - #end if - - #if str($add_tag) == "add_tag_true": - -t - #end if - - #if str($prior) != "": - -p $prior - #end if - - #if str($min_match) != "": - -n $min_match - #end if - - #if str($min_keep) != "": - -M $min_keep - #end if - - #if str($matches_file) == "matches_file_true": - -m $output_matches - #end if - - -o $output_trimmed $input_fastq 2>&1 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - (matches_file == True) - - - - -Scythe uses a Naive Bayesian approach to classify contaminant substrings in sequence reads. It considers quality information, which can make it robust in picking out 3'-end adapters, which often include poor quality bases. - -Most next generation sequencing reads have deteriorating quality towards the 3'-end. It's common for a quality-based trimmer to be employed before mapping, assemblies, and analysis to remove these poor quality bases. However, quality-based trimming could remove bases that are helpful in identifying (and removing) 3'-end adapter contaminants. Thus, it is recommended you run Scythe before quality-based trimming, as part of a read quality control pipeline. - -The Bayesian approach Scythe uses compares two likelihood models: the probability of seeing the matches in a sequence given contamination, and not given contamination. Given that the read is contaminated, the probability of seeing a certain number of matches and mistmatches is a function of the quality of the sequence. Given the read is not contaminated (and is thus assumed to be random sequence), the probability of seeing a certain number of matches and mismatches is chance. The posterior is calculated across both these likelihood models, and the class (contaminated or not contaminated) with the maximum posterior probability is the class selected. - -Scythe will infer the quality type from the datatype of the file. - - -