I am trying to obtain the number of synonymous and non-synonymous sites for a gene. I know that ensembl provides attributes like "mmusculus_homolog_dn" and "mmusculus_homolog_ds", i.e. the dn and ds values for a gene given mouse outgroup comparison, where dn = #non-synonymous mutations/#non-synonymous sites, and ds = #synonymous mutations/#synonymous sites. I need the denominators of these terms, i.e. the number of synonymous/non-synonymous sites in a gene (i.e. the number of possible silent and non-silent mutations per site summed over all sites in the cds). I searched the attribues page for biomart and nothing obvious came up with those terms, but I assume that this information is there with some attribute name that I couldn't identify.
Alternatively, if this information is not available from ensembl, is there another database that would have it?