* This version inherits from the original SW implementation so it can use the same matrix creation method.
* A bunch of refactoring was done to the original version to clean it up a bit and to have it do the
right thing for indels at the edges of the alignments.
* Enum added for the overhang strategy to use; added implementation for the INDEL version of this strategy.
* Lots of systematic testing added for this implementation.
* NOT HOOKED UP TO HAPLOTYPE CALLER YET. Committing so that people can play around with this for now.
Problem
-------
The DeBruijn assembler was too slow. The cause of the slowness was the need to construct many kmer graphs (from max read length in the interval to 11 kmer, in increments of 6 bp). This need to build many kmer graphs was because the assembler (1) needed long kmers to assemble through regions where a shorter kmer was non-unique in the reference, as we couldn't split cycles in the reference (2) shorter kmers were needed to be sensitive to differences from the reference near the edge of reads, which would be lost often when there was chain of kmers of longer length that started before and after the variant.
Solution
--------
The read threading assembler uses a fixed kmer, in this implementation by default two graphs with 10 and 25 kmers. The algorithm operates as follows:
identify all non-unique kmers of size K among all reads and the reference
for each sequence (ref and read):
find a unique starting position of the sequence in the graph by matching to a unique kmer, or starting a new source node if non exist
for each base in the sequence from the starting vertex kmer:
look at the existing outgoing nodes of current vertex V. If the base in sequence matches the suffix of outgoing vertex N, read the sequence to N, and continue
If no matching next vertex exists, find a unique vertex with kmer K. If one exists, merge the sequence into this vertex, and continue
If a merge vertex cannot be found, create a new vertex (note this vertex may have a kmer identical to another in the graph, if it is not unique) and thread the sequence to this vertex, and continue
This algorithm has a key property: it can robustly use a very short kmer without introducing cycles, as we will create paths through the graph through regions that aren't unique w.r.t. the sequence at the given kmer size. This allows us to assemble well with even very short kmers.
This commit includes many critical changes to the haplotype caller to make it fast, sensitive, and accurate on deep and shallow WGS and exomes, the key changes are highlighted below:
-- The ReadThreading assembler keeps track of the maximum edge multiplicity per sample in the graph, so that we prune per sample, not across all samples. This change is essential to operate effectively when there are many deep samples (i.e., 100 exomes)
-- A new pruning algorithm that will only prune linear paths where the maximum edge weight among all edges in the path have < pruningFactor. This makes pruning more robust when you have a long chain of bases that have high multiplicity at the start but only barely make it back into the main path in the graph.
-- We now do a global SmithWaterman to compute the cigar of a Path, instead of the previous bubble-based SmithWaterman optimization. This change is essential for us to get good variants from our paths when the kmer size is small. It also ensures that we produce a cigar from a path that only depends only the sequence of bases in the path, unlike the previous approach which would depend on both the bases and the way the path was decomposed into vertices, which depended on the kmer size we used.
-- Removed MergeHeadlessIncomingSources, which was introducing problems in the graphs in some cases, and just isn't the safest operation. Since we build a kmer graph of size 10, this operation is no longer necessary as it required a perfect match of 10 bp to merge anyway.
-- The old DebruijnAssembler is still available with a command line option
-- The number of paths we take forward from the each assembly graph is now capped at a factor per sample, so that we allow 128 paths for a single sample up to 10 x nSamples as necessary. This is an essential change to make the system work well for large numbers of samples.
-- Add a global mismapping parameter to the HC likelihood calculation: The phredScaledGlobalReadMismappingRate reflects the average global mismapping rate of all reads, regardless of their mapping quality. This term effects the probability that a read originated from the reference haploytype, regardless of its edit distance from the reference, in that the read could have originated from the reference haplotype but from another location in the genome. Suppose a read has many mismatches from the reference, say like 5, but has a very high mapping quality of 60. Without this parameter, the read would contribute 5 * Q30 evidence in favor of its 5 mismatch haplotype compared to reference, potentially enough to make a call off that single read for all of these events. With this parameter set to Q30, though, the maximum evidence against the reference that this (and any) read could contribute against reference is Q30. -- Controllable via a command line argument, defaulting to Q60 rate. Results from 20:10-11 mb for branch are consistent with the previous behavior, but this does help in cases where you have rare very divergent haplotypes
-- Reduced ActiveRegionExtension from 200 bp to 100 bp, which is a performance win and the large extension is largely unnecessary with the short kmers used with the read threading assembler
Infrastructure changes / improvements
-------------------------------------
-- Refactored BaseGraph to take a subclass of BaseEdge, so that we can use a MultiSampleEdge in the ReadThreadingAssembler
-- Refactored DeBruijnAssembler, moving common functionality into LocalAssemblyEngine, which now more directly manages the subclasses, requiring them to only implement a assemble() method that takes ref and reads and provides a List<SeqGraph>, which the LocalAssemblyEngine takes forward to compute haplotypes and other downstream operations. This allows us to have only a limited amount of code that differentiates the Debruijn and ReadThreading assemblers
-- Refactored active region trimming code into ActiveRegionTrimmer class
-- Cleaned up the arguments in HaplotypeCaller, reorganizing them and making arguments @Hidden and @Advanced as appropriate. Renamed several arguments now that the read threading assembler is the default
-- LocalAssemblyEngineUnitTest reads in the reference sequence from b37, and assembles with synthetic reads intervals from 10-11 mbs with only the reference sequence as well as artificial snps, deletions, and insertions.
-- Misc. updates to Smith Waterman code. Added generic interface to called not surpisingly SmithWaterman, making it easier to have alternative implementations.
-- Many many more unit tests throughout the entire assembler, and in random utilities
-- Code was undocumented, big, and not well tested. All three things fixed.
-- Currently not passing, but the framework works well for testing
-- Added concat(byte[] ... arrays) to utils
-- The new code includes a new mode to write out a BAM containing reads realigned to the called haplotypes from the HC, which can be easily visualized in IGV.
-- Previous functionality maintained, with bug fixes
-- Haplotype BAM writing code now lives in utils
-- Created a base class that includes most of the functionality of writing reads realigned to haplotypes onto haplotypes.
-- Created two subclasses, one that writes all haplotypes (previous functionality) and a CalledHaplotypeBAMWriter that will only write reads aligned to the actually called haplotypes
-- Extended PerReadAlleleLikelihoodMap.getMostLikelyAllele to optionally restrict set of alleles to consider best
-- Massive increase in unit tests in AlignmentUtils, along with several new powerful functions for manipulating cigars
-- Fix bug in SWPairwiseAlignment that produces cigar elements with 0 size, and are now fixed with consolidateCigar in AlignmentUtils
-- HaplotypeCaller now tracks the called haplotypes in the GenotypingEngine, and returns this information to the HC for use in visualization.
-- Added extensive docs to HaplotypeCaller on how to use this capability
-- BUGFIX -- don't modify the read bases in GATKSAMRecord in LikelihoodCalculationEngine in the HC
-- Cleaned up SWPairwiseAlignment. Refactored out the big main and supplementary static methods. Added a unit test with a bug TODO to fix what seems to be an edge case bug in SW
-- Integration test to make sure we can actually write a BAM for each mode. This test only ensures that the code runs and doesn't exception out. It doesn't actually enforce any MD5s
-- HaplotypeBAMWriter also left aligns indels in the reads, as SW can return a random placement of a read against the haplotype. Calls leftAlign to make the alignments more clear, with unit test of real read to cover this case
-- Writes out haplotypes for both all haplotype and called haplotype mode
-- Haplotype writers now get the active region call, regardless of whether an actual call was made. Only emitting called haplotypes is moved down to CalledHaplotypeBAMWriter
-- Has the overall effect that the GATK user AWS keys are no longer visible in the gatk source as plain text. This will stop AWS from emailing me (they crawl the web looking for keys)
-- Added utility EncryptAWSKeys that takes as command line arguments the GATK user AWS access and secret keys, encrypts them with the GATK private key, and writes out the resulting file to resources in phonehome.
-- GATKRunReport now decrypts as needed these keys using the GATK public key as resources in the GATK bundle
-- Refactored the essential function of Resource (reading the resource) from IOUtils into the class itself. Now how to get the data in the resouce is straightforward
-- Refactored md5 calculation code from a byte[] into Utils. Added unit tests
-- Committing the encrypted AWS keys
-- #resolves https://jira.broadinstitute.org/browse/GSA-730
Eric Banks
Mark DePristo
Mauricio Carneiro
David Roazen