Figure 4

Histogram of nucleotide differences between native mouse annotations and predictions from human. (a) After excluding exact matches between the native mouse annotations and exon coordinates predicted from translated human annotations, the differences for coding genes show a pronounced periodicity of multiples of three nucleotides, consistent with differences in amino acid counts between species, rather than mapping or alignment errors. (b) By contrast, non-coding RNAs do not show any periodicity, consistent with these sequences not being subject to translation and thus free of constraint to preserve multiplicity.