picard EstimateLibraryComplexity

Identifier: TL_e24fa5_2f.c8

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Estimates the numbers of unique molecules in a sequencing library. This tool outputs quality metrics for a sequencing library preparation. Library complexity refers to the number of unique DNA fragments present in a given library. Reductions in complexity resulting from PCR amplification during library preparation will ultimately compromise downstream analyses via an elevation in the number of duplicate reads. PCR-associated duplication artifacts can result from: inadequate amounts of starting material (genomic DNA, cDNA, etc.), losses during cleanups, and size selection issues. Duplicate reads can also arise from optical duplicates resulting from sequencing-machine optical sensor artifacts. This tool attempts to estimate library complexity from sequence of read pairs alone. Reads are sorted by the first N bases (5 by default) of the first read and then the first N bases of the second read of a pair. Read pairs are considered to be duplicates if they match each other with no gaps and an overall mismatch rate less than or equal to MAX_DIFF_RATE (0.03 by default). Reads of poor quality are filtered out to provide a more accurate estimate. The filtering removes reads with any poor quality bases as defined by a read's MIN_MEAN_QUALITY (20 is the default value) across either the first or second read. Unpaired reads are ignored in this computation. The algorithm attempts to detect optical duplicates separately from PCR duplicates and excludes these in the calculation of library size. Also, since there is no alignment information used in this algorithm, an additional filter is applied to the data as follows. After examining all reads, a histogram is built in which the number of reads in a duplicate set is compared with the number of of duplicate sets. All bins that contain exactly one duplicate set are then removed from the histogram as outliers prior to the library size estimation.


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