Do you mean the distribution of all transcripts produced by all loci in a given organism? If so, would you expect a different shaped distribution if you considered only one transcript per locus versus all known isoforms from that locus? Or are you looking for something more relative, such as the range of isoform sizes produced per locus, per organism?
Have you given a look to the Ensembl Genome browser?
Just write the name/ID of the gene, and it will take you to a result page like this. In this example, i've done it for gorilla BRCA2, and in there you get all the isoforms and its length, for this gene (isoforms are given with this kind of identifier ENSZZZTXXXXXXXXXX, with "T" standing for "transcript", "Z" describing the species, and "Xs" is the ID).
If you are familiar with the Ensemble Compara API, you can do it programatically through it... :)
Hmmm... I don't know for sure if you can do it with the API... But it makes sense to me it could be possible, even if i'm not familiar with that API.
Otherwise, you will have to retrieve the info you want manually on the link above for each isoform for each gene.
Do you mean the distribution of all transcripts produced by all loci in a given organism? If so, would you expect a different shaped distribution if you considered only one transcript per locus versus all known isoforms from that locus? Or are you looking for something more relative, such as the range of isoform sizes produced per locus, per organism?
I mean all the transcripts in a given organism.
Good follow up. I agree that this question could use a bit more clarification...