[AanaNahum]

Nice helpful answers I was also about to ask the similar question and found it already here.

[Ric69]

Here's a nice uncomplicated summary of hg19... https://grch37.ensembl.org/Homo_sapiens/Info/Annotation

[zzta]

Sorry to revive this thread, but exons or CDSs are not the only thing transcribed, so how can we account for non-coding RNAs? My understanding is that they are also part of the transcriptome...

[steven]

Just to throw my 2 Cents in. As far as I know most exome-enriching kits use the CDS database for generating the exome library. As this database is less comprehensive than the Refseq or knownGene annotations in UCSC some exons will be missed due to that. Of course others are discarded because of hybridization difficulties (repetitive regions, etc).

That makes sense, thanks.

[steven]

I keep seeing a figure of 30-33Mb for the human exome e.g.

This 2009 Nature paper

http://www.nature.com/nature/journal/v461/n7261/edsumm/e090910-11.html

"Protein-coding regions constitute ~1% of the human genome or ~30 megabases (Mb), split across ~180,000 exons."

30-33Mb is also the figure cited in Illumina's "Sequencing Output Calculator' , sent to me by tech support.

Anyone know why the number is so much higher on this thread?

Because "protein coding regions" and "exons" are different things. UTRs can be long, especially in human.

I think it is important to know what we are talking about:

1. number of genomic positions that are annotated as coding (included in CDS)
2. number of genomic positions that are annotated as exonic (included in exons)

As frozenlyse and Richard Finney indicated, values for 2. range around 60 and 80Mb, depending on the annotation source.
Ssully, the citation you mention with the number of 30Mb refers to 1. ("protein coding regions").
Rstarke, what is this number of 1 billion referring to? "Annotated bases" can be anything, on a genome you can annotate introns, promoters, repeated regions.. a link to this information would help.
Now, is there a precise definition of "exome" or is it a loose term? Is it supposed to include coding regions only, or can anyone put in there some UTR, promoters, intronic flanks, etc?

[ulz_peter]

Just to throw my 2 Cents in. As far as I know most exome-enriching kits use the CDS database for generating the exome library. As this database is less comprehensive than the Refseq or knownGene annotations in UCSC some exons will be missed due to that. Of course others are discarded because of hybridization difficulties (repetitive regions, etc).

[Richard Finney]

Our friend Mr. Ref Seq says ...

Back of the envelope calculations:
The sum of the values for base coverage of the exons for the data above in the hg19/UCSCknown table (posted above) is
81,105,734

The Refseq table from UCSC for hg19 (jan 2011 version) says : 63,995,498
[ method : load table into datastruct, sort by name, traverse, if (currentname==previousname) dont count else calculate sum of exons and add to sum]. Notabene: this won't eliminate some overlapping situations.

Refseq is more conservative than UCSCknown and relies more on hand curation and less on computation.

I don't know about GENCODE but if it's that for human only and that number is right then it's probably any transcript ever measured. I could only speculate on what that extra bonus coverage is. A free trip to Sweden goes to the guy that can explain and prove it (if it's functionally real).

[rstarke]

I would also like to know why the huge discrepancy between what's in the literature (~30-40Mb) and the numbers cited in this thread. I just checked the GENCODE v6 annotations and the total annotated base count is over a billion, supporting the estimates in this thread. I'm confused. Can anyone clear up the discrepancy?

[ssully]

I keep seeing a figure of 30-33Mb for the human exome e.g.

This 2009 Nature paper

http://www.nature.com/nature/journal/v461/n7261/edsumm/e090910-11.html

"Protein-coding regions constitute ~1% of the human genome or ~30 megabases (Mb), split across ~180,000 exons."

30-33Mb is also the figure cited in Illumina's "Sequencing Output Calculator' , sent to me by tech support.

Anyone know why the number is so much higher on this thread?

[NextGenSeq]

By comparing the genes listed in the bed file to the UCSC annotation. I tried attaching the bed file but it's too large for this site to allow it.

[bioinfosm]

I assume you are interested in this since you are doing whole exome sequence enrichment and subsequent sequencing.

Different vendors have different amounts of "whole exome" coverage. We found that the Agilent Sure Select only enriches for ~89% of the human whole exome.

NextGenSeq, how did you get the number of ~89% exome targetted by agilent? Could you share some detail on that!

Thanks,
sm

[NextGenSeq]

I assume you are interested in this since you are doing whole exome sequence enrichment and subsequent sequencing.

Different vendors have different amounts of "whole exome" coverage. We found that the Agilent Sure Select only enriches for ~89% of the human whole exome.

[apratap]

Thanks Guys. I understand that it is acceptable to remove redundancy at exon level.

@frozenlyse : your end number (exons) seems to match mine.

How do I deal with gene level coverage. There are many genes which overlap each other and as noted in my first post.

Total # bases in RefSeq Genes : 2,011,862,672

Is it acceptable to remove redundancy while counting bases in all human genes. In a way this will lead us to underestimate coverage. I say so because overlapping genes can be coexpressed right >>?

Thanks for your time to help me understand this.

Best,
-Abhi

[frozenlyse]

If you just want a base pair count for different annotations, you can just use UCSC table browser, choose the genome build you are using and annotation you are interested in, and press "summary/statistics" at the bottom, eg for hg18 RefSeq you get

item count 34,702
item bases 1,166,592,699 (40.49%)
item total 2,020,112,601 (70.11%)
smallest item 33
average item 58,213
biggest item 2,304,634
block count 347,347
block bases 66,601,430 (2.31%)
block total 104,526,351 (3.63%)
smallest block 3
average block 301
biggest block 59,461


The "block" lines are what you are interested in: 347,347 exons from 34,702 Refseq genes, with total size of 104MB, however when removing redundancies 66Mb is covered

[steven]

Clearly there are overlapping regions in each of these annotation files [...] Just wondering if I should count the bases common to two genes twice or only uniq regions should be counted.

Most of the transcribed nucleotides of the human genome are represented in different transcripts (whatever they are considered as same "gene" or not). As Bio.X2Y pointed out, you definitely have to remove redundancy. You can send your annotations to galaxy or use BEDtools to "collapse" ("project"/"fusion"/"merge") your annotated exons before adding the lengths.