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Friday, February 5, 2010

GFF3 undocumented feature...

Earlier today, I tweeted:
Does anyone know how to decypher a diBase GFF3 file? They don't identify the "most abundant" nucleotide uniquely. seems useless to me.
Apparently, there is a solution, albeit undocumented:

The attribute "genotype" contains an IUB code that is limited to using either a single base or a double base annotation (eg, it should not contain, H, B, V, D or N - but may contain R, Y, W, S, M or K ), which then allows you to subtract the "reference" attribute (that must be canonical) from the "genotype" attribute IUB code to obtain the new SNP - but only when the "genotype" attribute is not a canonical base.

If only that were documented somewhere...

UPDATE: Actually, this turns out not to be the case at all -- there are still positions for which the "genotype" attribute is an IUB code, and the reference is not one of the called bases. DOH!

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Wednesday, December 16, 2009

one lane is not enough....

Without giving too much away about the stuff I'm working on - trying to study anything of interest in one lane of RNA-Seq data is futile. Do not try this at home kids.

Now, the question is, how valid is it to compare 36bp reads to 72bp reads? Ah, the joys of research.

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Wednesday, October 14, 2009

Useful error messages.... and another format rant.

I'll start with the error message, since it had me laughing, while everything else seems to have the opposite reaction.

I sent a query to Biomart the other day, as I often do. Most of the time, I get back my results quickly, and have no problems whatsoever. It's one of my "go-to" sites for useful genomic data. Unfortunately, every time I tried to download the results of my query, I'd get 2-3Mb into the file before the download would die. (It was a LONG list of snps, and the file size was supposed to be in the 10Mb ballpark.)

Anyhow, in frustration, I tried the "email results to you" option, whereupon I got the following email message:

Your results file FAILED.
Here is the reason why:
Error during query execution: Server shutdown in progress

That has to be the first time I've ever had a server shutdown cause a result failure. Ok, it's not that funny, but I am left wondering if that was the cause of the other 10 or so aborted downloads. Anyone know if Biomart runs on Microsoft products? (-;

The other thing on my mind this afternoon is that I am still looking to see my first Variant Call Format file for SNPs. A while back, I was optimistic about seeing the VCF files in the real world. Not that I can complain, but I thought adoption would be a little faster. A uniform SNP format would make my life much more enjoyable - I now have 7 different SNP format iterators to maintain, and would love to drop most of them.

What surprised me, upon further investigation, is that I'm also unable to find a utility that actually creates VCF files from .map, SAM/BAM, eland, bowtie or even pileup files. I know of only one SNP caller that creates VCF compatible files, and unfortunately, it's not freely available, which is somewhat un-helpful. (I don't know when or if it will be available, although I've heard rumours about it being put into our pipeline...)

That's kind of a sad state of affairs - although I really shouldn't complain. I have more than enough work on my plate, and I'm sure the same can be said for those who are actively maintaining SNP callers.

In the meantime, I'll just have to sit here and be patient... and maybe write an 8th snp format iterator.

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Friday, September 4, 2009

Variant Call Format

After earlier discussions, there is now some information available on the Variant Call Format available to the public.

If you're intrested in working with snps, this may be required reading:

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Friday, August 21, 2009

SNP Database v0.2

My SNP database is now up and running, with the first imports of data working well. That's a huge improvement over the v0.1, where the data had to be entered under pretty tightly controlled circumstances. The API now uses locks, better indexes, and I've even tuned the database a little. (I also cheated a little and boosted the P4 running it to 1Gb RAM.)

So, what's most interesting to me? Some of the early stats:

11,545,499 snps in total, made from:
  • 870549 snp calls from the 1000 genome project
  • 11361676 snps from dbsnp
So, some quick math:
11,361,676 + 870,549 - 11,545,499 = 686,726 Snps that overlapped between the 1000 genome project (34 data sets) and the dbSNP calls.

That is a whopping 1.6% of the SNPs in my database were not previously annotated in dbSNP.

I suppose that's not a bad thing, since those samples were all "normals", and it's good to get some sense as to how big dbSNP really is.

Anyhow, now the fun with the database begins. A bit of documentation, a few scripts to start extracting data, and then time to put in all of the cancer datasets....

This is starting to become fun.

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Tuesday, August 18, 2009

new repository of second generation software

I finally have a good resource for locating second gen (next gen) sequencing analysis software. For a long time, people have just been collecting it on a single thread in the bioinformatics section of the forum, however, the brilliant people at SeqAnswers have spawned off a wiki for it, with an easy to use form. I highly recommend you check it out, and possibly even add your own package.

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Monday, August 17, 2009

SNP Datatabase v0.1

Good news, my snp database seems to be in good form, and is ready for importing SNPs. For people who are interested, you can download the Vancouver Short Read Package from SVN, and find the relevant information in

There's a schema for setting up the tables and indexes, as well as applications for running imports from maq SNP calls and running a SNP caller on any form of alignment supported by FindPeaks (maq, eland, etc...).

At this point, there are no documents on how to use the software, since that's the plan for this afternoon, and I'm assuming everyone who uses this already has access to a postgresql database (aka, a simple ubuntu + psql setup.)

But, I'm ready to start getting feature requests, requests for new SNP formats and schema changes.

Anyone who's interested in joining onto this project, I'm only a few hours away from having some neat toys to play with!

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Thursday, August 6, 2009

New Project Time... variation database

I don't know if anyone out there is interested in joining in - I'm starting to work on a database that will allow me to store all of the snps/variations that arise in any data set collected at the institution. (Or the subset to which I have the right to harvest snps, anyhow.) This will be part of the Vancouver Short Read Analysis Package, and, of course, will be available to anyone allowed to look at GPL code.

I'm currently on my first pass - consider it version 0.1 - but already have some basic functionality assembled. Currently, it uses a built in snp caller to identify locations with variations and to directly send them into a postgresql database, but I will shortly be building tools to allow SNPs from any snp caller to be migrated into the db.

Anyhow, just putting it out there - this could be a useful resource for people who are interested in meta analysis, and particularly those who might be interested in collaborating to build a better mousetrap. (=

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Wednesday, March 25, 2009

Searching for SNPs... a disaster waiting to happen.

Well, I'm postponing my planned article, because I just don't feel in the mood to work on that tonight. Instead, I figured I'd touch on something a little more important to me this evening: WTSS SNP calls. Well, as my committee members would say, they're not SNPs, they're variations or putative mutations. Technically, that makes them Single Nucleotide Variations, or SNVs. (They're only polymorphisms if they're common to a portion of the population.

In this case, they're from cancer cell lines, so after I filter out all the real SNPs, what's left are SNVs... and they're bloody annoying. This is the second major project I've done where SNP calling has played a central role. The first was based on very early 454 data, where homopolymers were frequent, and thus finding SNVs was pretty easy: they were all over the place! After much work, it turned out that pretty much all of them were fake (false positives), and I learned to check for homopolymer runs - a simple trick, easily accomplished by visualizing the data.

We moved onto Illumina, after that. Actually, it was still Solexa at the time. Yes, this is older data - nearly a year old. It wasn't particularly reliable, and I've now used several different aligners, references and otherwise, each time (I thought) improving the data. We came down to a couple very intriguing variations, and decided to sequence them. After several rounds of primer design, we finally got one that worked... and lo and behold. 0/2. Neither of them are real. So, now comes the post-mortem: Why did we get the false positives this time? Is it bias from the platform? Bad alignments? Or something even more suspicious... do we have evidence of edited RNA? Who knows. The game begins all over again, in the quest for answering the question "why?" Why do we get unexpected results?

Fortunately, I'm a scientist, so that question is really something I like. I don't begrudge the last year's worth of work - which apparently is now more or less down the toilet - but I hope that the why leads to something more interesting this time. (Thank goodness I have other projects on the go, as well!)

Ah, science. Good thing I'm hooked, otherwise I'd have tossed in the towel long ago.

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Wednesday, October 8, 2008

Maq Bug

I came across an interesting bug today, when trying to work with reads aligned by Smith-Waterman (flag = 130), in PET alignments. Indeed, I even filed a Bug Report on it.

The low down on the "bug" or "feature" (I'm not sure which it is yet), is that sequences containing deletions don't actually show the deletions - they show the straight genomic sequence at that location. The reason that I figure this is a bug instead of by design is because sequences with insertions show the insertion. So why the discrepancy?

Anyhow, the upshot of it is that I'm only able to use 1/2 of the Smith-Waterman alignments maq produces when doing SNP calls in my software. (I can't trust that the per-base quality scores align to the correct bases with this bug) Since other people are doing SNP calls using MAQ alignments... what are they doing?

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Tuesday, July 22, 2008

SNP calling from MAQ

With that title, you're probably expecting a discussion on how MAQ calls snps, but you're not going to get it. Instead, I'm going to rant a bit, but bear with me.

Rather than just use the MAQ snp caller, I decided to write my own. Why, you might ask? Because I already had all of the code for it, my snp caller has several added functionalities that I wanted to use, and *of course*, I thought it would be easy. Was it, you might also ask? No - but not for the reasons you might expect.

I spent the last 4 days doing nothing but working on this. I thought it would be simple to just tie the elements together: I have a working .map file parser (don't get me started on platform dependent binary files!), I have a working snp caller, I even have all the code to link them together. What I was missing was all of the little tricks, particularly the ones for intron-spanning reads in transcriptome data sets, and the code that links together the "kludges" with the method I didn't know about when I started. After hacking away at it, bit by bit things began to work. Somewhere north of 150 code commits later, it all came together.

If you're wondering why it took so long, it's three fold:

1. I started off depending on someone else's method, since they came up with it. As is often the case, that person was working quickly to get results, and I don't think they had the goal of writing production quality code. Since I didn't have their code (though, honestly, I didn't ask for it either since it was in perl, which is another rant for another day) it took a long time to settle all of the 1-off, 2-off and otherwise unexpected bugs. They had given me all of the clues, but there's a world of difference between being pointed in the general direction towards your goal and having a GPS to navigate you there.

2. I was trying to write code that would be re-usable. That's something I'm very proud of, as most of my code is modular and easy to re-purpose in my next project. Half way through this, I gave up: the code for this snp calling is not going to be re-usable. Though, truth be told, I think I'll have to redo the whole experiment from the start at some point because I'm not fully satisfied with the method, and we won't be doing it exactly this way in the future. I just hope the change doesn't happen in the next 3 weeks.

3. Name space errors. For some reason, every single person has a different way of addressing the 24-ish chromosomes in the human genome. (Should we include the mitochondrial genome in our own?) I find myself building functions that strip and rename chromosomes all the time, using similar rules. Is the Mitochondrial genome a "MT" or just "M"? What case do we use for "X" and "Y" (or is it "x" and "y"?) in our files? Should we pre-pend "chr" to our chromsome names? And what on earth is "chr5_random" doing as a chromosome? This is even worse when you need to compare two active indexes, plus the strings in each read... bleh.

Anyhow, I fully admit that SNP calling isn't hard to do. Once you've read all of your sequences in, determined which bases are worth keeping (prb scores), determined the minimum level of coverage, minimum number of bases that are needed to call a snp, there's not much left to do. I check it all against the Ensembl database to determine which ones are non-synonymous, and then: tada, you have all your snps.

However, once you're done all of this, you realize that the big issue is that there are now too many snp callers, and everyone and their pet dog is working on one. There are several now in use at the GSC: Mine, at least one custom one that I'm aware of, one built into an aligner (Bad Idea(tm)) under development here and the one tacked on to the swiss army knife of aligners and tools: MAQ. Do they all give different results, or is one better than another? who knows. I look forward to finding someone who has the time to compare, but I really doubt there's much difference beyond the alignment quality.

Unfortunately, because the aligner field is still immature, there is no single file output format that's common to all aligners, so the comparison is a pain to do - which means it's probably a long way off. That, in itself, might be a good topic for an article, one day.

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