Hello,
The only problem I see with this approach is that Alt Events data 
represent exons changes that appear less often than the majority. If you 
exclude transcripts with these regions by base overlap, you will miss 
well represented exons.

For example: In the latest human, hg18
Set tracks UCSC Genes, Alt Events, CCDS, and RefSeq Genes to pack, turn 
everything else on to hide.
Set position/search to chr21:9,934,842-9,941,996

This feature in the Alt Events track represents a single transcript that 
is missing the exon.
Item: cassetteExon
Position: chr21:9938241-9938346
The majority of transcripts do have the exon. So excluding transcripts 
that have base overlap with this feature will give you the opposite 
results than intended.

A track like CCDS represents a very conservative set of coding 
sequences. One relevant line from this track's description page is "This 
project is a collaborative effort to identify a core set of human 
protein-coding regions that are consistently annotated and of high 
quality." Read the complete track description (and links to the 
contributor's web site) to see if this is useful for you.

Also, have you examined the data contained in the "knownCanonical" 
table? You can find this table in the Table browser under the UCSC Genes 
track. "Format description: Describes the canonical splice variant of a 
gene". This may be what you are looking for.

If I have misunderstood, please write back with an example and we can 
work out the details,
Jennifer Jackson
UCSC Genome Bioinformatics Group

ps. knownAlt is the primary table of the Alt Events track, so I am 
making the assumption that there was a small error in your query 
description and that you meant that you were going to compare knownGenes 
with knownAlt by base overlap.

Clancy, Kevin wrote:
> Dear Sirs
> I am interested in identifying constant exons within the Genes and gene
> prediction Tracks. I understand that I can find alternative splice exons
> within the Alt Events track. And I can find all exons for a given gene
> within the UCSC genes track. So if create an intersection with Known Alt
> table that has no overlap with Alt Events, I want to confirm that the
> result of this would be constant exons that appear in the majority of
> transcripts associated with a given gene.
> Thanks
> kevin
>  
> Kevin Clancy, PhD
> Senior Scientist
> Informatics & eCommerce
> Life Technologies
> 5791 Van Allen Way
> Carlsbad CA 92008
> phone: 760 268 8356
> cell: 240 417 8604
> email: [email protected]
>  
> _______________________________________________
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>   
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